# Real world experiences using radar -- how far can your radar really "see"? MARPA?



## Bene505 (Jul 31, 2008)

*Real world experiences using radar -- how far can your radar really "see"? MARPA?*

I'm doing some online shopping for a radar for our Beneteau 50. It looks like there are 24 nm, 48 nm and 72 nm radars. If I'm only mounting the radar 15 feet off the deck, will I be wasting money/windage/weight if I get a 48 nm range? The 48 nm ones tend to be 24 inch radomes instead of 18 inch.

Note: I know about the line-of-sight calculations and have seen a site or two that helps you calculate it. But I heard that radar bends, so those equations aren't completely accurate.

What's your real-world experience using radar, distance-wise. How far away can you "see" ships? (And did MARPA work for you?)


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## sailingdog (Mar 19, 2006)

The 24" radomes will have better resolution than the 18" since the beam will be narrower generally speaking. Just remember that radar is good for distances but not very accurate for bearings. The new HD ones from Garmin are very nice, at least from what I've seen and heard. I don't own one, but installed two of them this past season. 

As for mounting it...be aware that the higher you mount the radome, the greater effect boat pitch and rolling will have on it. Mounting higher also increases the effective range, but that works at both the near and far ends... and if it is mounted too high, you'll lose the ability to use it close in to the boat—where it is probably more important.


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## Cruisingdad (Jul 21, 2006)

Bene505 said:


> I'm doing some online shopping for a radar for our Beneteau 50. It looks like there are 24 nm, 48 nm and 72 nm radars. If I'm only mounting the radar 15 feet off the deck, will I be wasting money/windage/weight if I get a 48 nm range? The 48 nm ones tend to be 24 inch radomes instead of 18 inch.
> 
> Note: I know about the line-of-sight calculations and have seen a site or two that helps you calculate it. But I heard that radar bends, so those equations aren't completely accurate.
> 
> What's your real-world experience using radar, distance-wise. How far away can you "see" ships? (And did MARPA work for you?)


I would estimate my radar as being about 25 feet off the water or so. Here is a pic, you can guess for yourself. I have the MARPA function, but have never used it in a real world situation.










One of the buggest plusses of a larger radar is not how far out it sees, but the resolution. The larger domes have a narrower beamwidth that allows better clarity. How this affects a boater is that it might pick up two ships/boats instead of one - especially on the horizon. As the distance goes further out, this beamwidth becomes increasingly more important (think of a triangle with the point being your boat).

Now how does this affect the sailor? Not a lot.

In order to get the maximum range via line of sight, you have to mount your radar higher up the mast. However, the higher you mount it, the more susceptible its losses/disruptions are to heeling. The more it heels/shakes, the less worthwhile any of that clarity is. Does that make sense?

In a magazine, it would seeem that for the modest amount of money more that a 4kw is versus a 2kw, it makes sense to get the 4kw for better clarity and distance. In the real world, in my experience, it makes no difference. The only way it would matter is if the seas are perfectly flat and you are motoring. If that is the case, why are you even using the radar??? The exception to this is to get a radar leveler in which case the clarity and distance of the 4kw would really become apparent. However, now you have really increased your cost, install, weight, and power.

Here is where radar has become very useful for us: At night - especially down the ICW. That is where overlay is especially helpful. You will then be able to see markers that are supposed to be there via the chartplotter/radar, and the ones that are NOT supposed to be there! Radar has avoided several collisions or close calls for me in those instances. It has also helped me to see storms that were coming out at sea and make preparations (unlike what others have said, I have never been able to steer around them).

For those in fog prone areas (which Florida is not), the radar's benefits are obvious.

I think you would be better off spending less money on the 24 and going with it. If you want to spend a bit more, get the leveller. But I think you would be fine without it.

THose are my opinions,

- CD


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## Maine Sail (Jan 6, 2003)

*Yes and no...*

Personally I don't see much benefit to a 48 mile dome over a 24nm or 36nm, in the case of the 18" Garmin, for on water distance. I prefer an 18" dome size for obvious reasons on a sail boat and currently Garmin packs the most performance into an 18" dome. The GMR 18 is a 4kw 36 mile unit but it's 18" isnead of 24".

As you go bigger in dome the screen resolution does get better because the beam width is narrower. I have used very large, and very expensive, 72 mile radars on mega yachts and large fishing vessels and the screen resolution is great but you still can't see beyond the curvature of the earth. Anyone who claims they can see anywhere near 24nm, 36nm, 48nm or 72nm, on water, is full of bull excrement.

What you can see with a bigger dome is weather but with the quality GPS weather subscriptions these days why bother adding all that weight & expense?

Beyond that the new High Def 18" domes are amazing! Furuno & Garmin have them & I believe Raymarine will. My Garmin was very, very sharp right out of the box and after a little tweaking matched resolutions and target displays of units much larger, and more expensive, that I have used.

I use radar a lot, being from Maine, and probably have well over 2000+ hours, perhaps more, (was a commercial fisherman for about 8 years in my younger days) and literally thousands of miles of time spent in the fog with radar. My suggestion is quite the opposite of dogs. Get the dome on the mast and get it high.

The junk Dog and I banter about with close in targets is just that junk, especially when it comes to the real world!

I have picked up kayaks at close range and many other close in targets with a dome on the mast. In my life there have only been a few instances, perhaps one or two, out of thousands of hours in thick fog, where I had so little vis that a lower dome would have even mattered. In contrast I have had hundreds of times when more range would have been better.

A dome, regardless of it's rated range, 10' off the water will see a 10' tall target at about 7.6 miles.

A dome 20' off the water will see a 10' tall target at roughly 9.2 miles.

Most mast mounts are roughly 25 feet high or more!!

Never under estimate the distance you'll need. We have a ferry up here called the "Cat" that runs at over 50 knots. A 6nm dome visibility is NOT enough in pea soup for a vessel traveling 50+ knots trust me.... If you sail in shipping lanes or high traffic areas you'll want as much distance as you can get.

The higher the better!!!

The first photo bellow shows our old boat with mast mounted radar. The second photo shows my neighbors boat which I could pick up clear as day with that mast mount. If you have not seen a target on your radar before it gets that close you have MUCH bigger issues like going back to the owners manual big!








Even with my spar mount on my Catalina 310 I could make out this neighbor, the C&C just behind my boat, clear as day and he has no reflector...









Our current boat has a pole mount radar and I will eventually move it back to the spar for better range performance. Keep in mind that a pole mount ten feet off the water, in ten foot seas, will lose targets and range performance every time you are not on the crest of a swell of a wave and when you get to the bottom of a 10-12 footer you will have zero target tracking ability until you begin to come back up and reach the crest again where the best performance will be. The has happened to me more than once with low domes.


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## davidpm (Oct 22, 2007)

May not qualify as real world but a good review if you haven't seen it already.
Boat marine Product Review/Test; Garmin GMR 18 marine radar review


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## chuck5499 (Aug 31, 2003)

i have a 24nm raymarine and just finished a run from miami to woods hole mass and back - i did not use radar a lot - main use was in fog, at sea especially at night and to use marpa to track big boats and how close we were going to get - 
the radar is mounted on a quest pole and gimballed - i would est it is 12-15' above the waterline - 
marpa worked well not so much to miss big boats in a narrow area - such as delaware bay or cheaspeake bay or those barges running close to shore at night - gives me peace of mind that i know how close we will be and if i think they will be to close can call them and determine their course and notify them that i will change mine - and i like peace of mind 
chuck and svsoulmates 
in miami for repairs before heading to the bahamas


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## Maine Sail (Jan 6, 2003)

davidpm said:


> May not qualify as real world but a good review if you haven't seen it already.
> Boat marine Product Review/Test; Garmin GMR 18 marine radar review


Good read, but poor quality photos?

Here is a shot of mine, right out of the box, and before I even tweaked any of the settings. HD is sharp!!


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## sailaway21 (Sep 4, 2006)

Range is basically a function of height and power. There is no substitute for either. Dog's comments on rolling are certainly valid though I am not as enamoured as he on using radar for close-in work.

You would not be wasting your money on the more powerful set as you'll reap better overall performance within the range constraints of your mounting height.

Now expected range is a bit of a touchy subject and it's not good to raise false expectations. I've used very high powered radars that could reach out over one hundred miles. It should be mentioned that this was with an antenna height well in excess of 100 feet over the waterline of the vessel. And I've picked up returns at that long range but only a certain type of return. This holds true for less powerful radars as well. The returns I got were high coast lines and mountains. But what image of the coastline was I seeing? Certainly not the beach edge. Perhaps the bluffs some distance back? Perhaps the tree lines even further back yet? Another words, all this technology was sufficient to tell me I was still in the Mediterranean Sea and south of Sicily. An idea which i already had some knowledge of. (g) Practically speaking, on a good quality commercial ship-mounted radar, 24 miles is the limit of the practical working scale for collision avoidance and navigation not much further depending on the uniqueness of the landmark being scanned.

On a sailboat you can expect substantially less but should understand that radar propagation varies tremendously with atmospheric conditions from day to day, or even time of day. I've picked up the southwest coast of Alaska at a range of 350 miles, even though my radar's max scale was 48 miles, under super refraction conditions. For six hours the ghost of the refracted signal was clear as a bell allowing me to see I was pointed directly at the Cook Inlet. Neat but, of little navigational use practically speaking.

A more powerful radar will punch through rain and mists more capably. It's easier to dampen the return via rain or sea clutter adjustments than to lack for return from a weaker unit. Range is important because you'll pick up larger targets at a greater distance. Larger targets are generally speaking the ones that are going to kill you, both due to size and speed. Things like ferries and container ships. You'll likely notice that some deep laden tankers do not show at the same range as, say, a container ship but they tend to be slower and you'll have more time to deal with them as they appear. You may only pick up a non-radar reflector equipped sailboat at six miles, if you're lucky, but your relative closing speed allows you ample time to act even then. Your biggest worry offshore, in my opinion, is the high speed ferry or container ship. At twenty five to thirty knots they can be upon you in no time. While you're unlikely to be able to take much evasive action in their regard, you are going to be able to reach out via radio and alert them to your presence in a timely matter. Because you won't show up on their screen nearly as well as they do on yours'.

MARPA, or automatic collision avoidance systems, are neither. The auto acquisition is of questionable utility as it is as likely to acquire and track a wave as it is a ship. And collision is only avoided by proper interpretation of the data received. One of the problems will be induced by the amount of yaw your boat is experiencing as well as the accuracy of the compass signal you're sending to the radar unit. You have to stabilize the radar image via some type of compass input for a MARPA system to work. Or, alternatively, you have to hold your course within a degree or two, and realize that, a change of course will require a complete recalculation of the data, about six minutes minimum. If you're yawing significantly, the radar will be near useless for collision avoidance or much else without some form of image stabilization via course input.

While not answering your specific questions, I hope this has helped. Personally, I think that radar is the greatest navigational and collision avoidance device invented in the last century or so. I'd take a good radar unit over six GPS units, Loran, or even my trusty sextant. The only thing I'd rank higher is the lowly fathometer, in terms of necessity for safe navigation. And a compass, of course.


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## goboatingnow (Oct 10, 2008)

Have to agree with sailaway. 
Rather then power the best antanna is the longest, as the horiztonal beam width reduces

Pole mounting is fine, I have had mast and pole mounted, would go back to mast as wave motion causes more clutter when pole mounted.

MARPA ( mini automatic radar plotting aid) is very questionable without a really good stable heading sensor, preferably a GPS compass ( wihich is not your average GPS, rather a RTK unit) or failing that a really good solid state heading sensor. Otherwise the yaw in your small boat confuses the vector calculation and what you see is the other boats vector line swinging all over the place along with huge changes in velocity. but hes not actually doing that its your boat yawing as sailaway says the recompute time on modern chartplotters tends to make the system then lag behind whats really happenning. However with a good heading sensor its is an amazing system

The current config I have is a 4 foot open array garmin and a Hemisphere GPS compass as a heading sensor and the result is just amazing.


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## Bene505 (Jul 31, 2008)

Wow, excellent replies! Time to hit the rep power button.

I have the heading sensor as part of the Raymarine Autopilot. So I guess I'll have to get a Raymarine radar? (Or are the Garmins ones interoperable somehow?) I really want to take advantage of MARPA.

Second question, why don't they make an elevation-adjusting array for use on sailboats. The elevation would cycle up and down as the array spins around and around. That way, heel wouldn't matter.


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## Bene505 (Jul 31, 2008)

After reading all this, I'm dreaming of a gimbled, 4 foot open array sitting right on top of the mast.

Somehow it might take getting used to the look of it. And I'll just have to add another couple inches to the bulb keel!! Let's see, she's got an iron keel, guess that's a welding job, right?

(A little tongue in cheek, but dreaming it none-the-less.)


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## Bene505 (Jul 31, 2008)

goboatingnow -- please send or post a picture. I'd like to see what a 4' open array looks like on a sailboat.

Just re-read everyone's input. There's some really good information in here.


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## Maine Sail (Jan 6, 2003)

Bene505 said:


> Wow, excellent replies! Time to hit the rep power button.
> 
> I have the heading sensor as part of the Raymarine Autopilot. So I guess I'll have to get a Raymarine radar? (Or are the Garmins ones interoperable somehow?) I really want to take advantage of MARPA.
> 
> Second question, why don't they make an elevation-adjusting array for use on sailboats. The elevation would cycle up and down as the array spins around and around. That way, heel wouldn't matter.


Perhaps I'm just old school but I've yet to use my Marpa. I've never had an incident where I had issues tracking targets so I have not yet had a need to flip on my Marpa. I believe that any heading sensor, if properly calibrated, will work through NEMA with the Garmin units..


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## N0NJY (Oct 19, 2008)

Bene505 said:


> I'm doing some online shopping for a radar for our Beneteau 50. It looks like there are 24 nm, 48 nm and 72 nm radars. If I'm only mounting the radar 15 feet off the deck, will I be wasting money/windage/weight if I get a 48 nm range? The 48 nm ones tend to be 24 inch radomes instead of 18 inch.
> 
> Note: I know about the line-of-sight calculations and have seen a site or two that helps you calculate it. But I heard that radar bends, so those equations aren't completely accurate.
> 
> What's your real-world experience using radar, distance-wise. How far away can you "see" ships? (And did MARPA work for you?)


Ummm.. simple question, VERY simple answer.

Radars, regardless of their "resolution" only "See" as far as the horizon.

If you're seeing something beyond the horizon, you're seeing planes or satellites.

Radio waves travel in a straight line at frequencies used by radar systems - thus you can and WILL ONLY have "Line of Sight". If it is daylight and there is something just visible on the horizon, the radar will "see" it. If it drops below visible horizon, the RADIO horizon is exactly the same.

(Of course, some people have better eyes that others too.......)


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## jimmalkin (Jun 1, 2004)

I agree with Maine Sail re Marpa. I've never had the need to use it and frankly feel that the less automated tracking and piloting, the better. I feel more comfortable with stuff that requires my attention to tracking each target and to finding point of approach. For me, like piloting with plotters and charts - the more interaction I have, the more focus I bring to the process.


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## N0NJY (Oct 19, 2008)

I should add something here...

Someone mentioned power.

Power, that is the wattage of a unit can increase your range - but also be aware that increasing your power by, say two times does not double your range. There is a mathematical function called the inverse-square law which both light waves and radio waves adhere to.

So if you want to get two times the distance - there's a decibel calculation that you need to see (so you're going to really quadruple the radio strength output) to double the distance. If you're doing that - and you're getting to the horizon - the radio signal is STILL going to travel in a straight light (a tangent to the earth's surface) and into space.

There is almost NO bending of RF by the ionosphere frequency ranges used in radar systems therefore, counting on any "bending" (technically this is refraction, not reflection) isn't going to occur, OR be useful on radar systems.


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## Cruisingdad (Jul 21, 2006)

Maine Sail said:


> Never under estimate the distance you'll need. We have a ferry up here called the "Cat" that runs at over 50 knots. A 6nm dome visibility is NOT enough in pea soup for a vessel traveling 50+ knots trust me.... If you sail in shipping lanes or high traffic areas you'll want as much distance as you can get.
> 
> The higher the better!!!
> 
> .


I dissagree with that. THe higher it is the more susceptible you will be to false returns. THis becomes especially true in poor weather conditions where the boat is rolling or pitching a lot. A "mid-mast" mount is perfectly acceptable. I guess that is about some 20-25 feet or so off the cabin top, depending on the boat/spar height.

It is all a trade off. As I said, you are better off spending more money on the leveller than a 4kw. Of course, with a 50+ foot boat, you could probably justify the weight aloft with a 4kw too (and leveler). But I strongly suspect that if you put a regular old 2kw up there without even a leveler, you will be happy 99% of your radar-use time. And you will be 100% happier on the non-radar use time.

Spend the rest on beer.

- CD


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## Cruisingdad (Jul 21, 2006)

jimmalkin said:


> I agree with Maine Sail re Marpa. I've never had the need to use it and frankly feel that the less automated tracking and piloting, the better. I feel more comfortable with stuff that requires my attention to tracking each target and to finding point of approach. For me, like piloting with plotters and charts - the more interaction I have, the more focus I bring to the process.


I have not used it either. However, I certainly am not opposed to it. I think that with all things electronic, it is only another tool to add to (and not take away from) good seamanship.

My opinion,

- CD


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## Maine Sail (Jan 6, 2003)

Cruisingdad said:


> I dissagree with that. THe higher it is the more susceptible you will be to false returns. THis becomes especially true in poor weather conditions where the boat is rolling or pitching a lot. A "mid-mast" mount is perfectly acceptable. I guess that is about some 20-25 feet or so off the cabin top, depending on the boat/spar height.
> 
> It is all a trade off. As I said, you are better off spending more money on the leveller than a 4kw. Of course, with a 50+ foot boat, you could probably justify the weight aloft with a 4kw too (and leveler). But I strongly suspect that if you put a regular old 2kw up there without even a leveler, you will be happy 99% of your radar-use time. And you will be 100% happier on the non-radar use time.
> 
> ...


And based on personal experience with a self leveling unit and multiple boats with pole and spar mounts I can say that these theories all sound well and good until you put them into practice in the real word..

I said above I live and sail in foggy Maine. I have owned a Questus, regular pole mount systems and multiple mast mount domes. The Questus was converted by me from a fixed Edson pole.

I currently own a boat with a conventional pole mount.

I NOTICED NO DISCERNIBLE PERFORMANCE DIFFERENCE BETWEEN THE QUESTUS PERFORMANCE AND THE CONVENTIONAL POLE MOUNT!!!

this was the same radar on the same boat using a fixed pole and a self leveling Questus unit. The Questus is a fine piece of gear, & very well built, but about 18 boats bucks more than you need to spend. Could even be more these days.

What I have seen and noticed consistently are significant differences between a pole level dome, either self leveling or fixed, and a mast mounted dome at 20-25 feet off the deck or so! I will, at some point, convert back to a mast mounted dome and ditch the pole mount I currently have. I am biased but not towards a mast mount because I currently own one and support it because thats "what I have" but rahter I am biased because time and time again I have seen and personally witnessed better performance from a dome mounter higher than lower.

Just so folks don't think I'm shooting from the hip, here are photos of just three different boats we've owned and three of the different radar set ups.
*Current Boat Pole Mount :*








*Questus Boat We Owned* :








*One of our boats with mast mount :*









When you sail in as much fog as we do there is no question a spar mounted dome is the best performing option.

I've Been using radar since the 1980's and have literally thousands of combined hours & miles of actual "in the fog" experience as I was a commercial lobsterman spending 60+ hours per week on the water. I've also used just about ever brand of radar and they all work, some better than others, but they all work..

For the flat bay conditions and short distances a pole is fine but for off shore work or rough seas, regardles of the theroretical "pitch and yaw" garbage I see bantered about there is no question in my mind that the higher the dome the better range and target performance you will get..

P.S. This boat we owned, like my commercial lobster boat, was one of the worst performers despite it having a 4kw dome, as it was only about 7-8 feet off the water..


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## Bene505 (Jul 31, 2008)

Maine Sail -- You are very giving of your time to us. Thank you!

And somehow you collect beautiful sailboats too.


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## sailaway21 (Sep 4, 2006)

Another debate sparked by the trend towards automatic operation of everything! MARPA is a computer driven resolver of the course and speed triangle involving two or more moving vessels. We used to do this by hand on what is known as a reflection plotter over the radar screen. The manufacturers, and the legislators, would like you to believe that the new radar's computer can do this better. It can to a degree as it's always updating. Where it falls down is in the area of weak signal returns such as given by fishing boats, sailboats, and submarine periscopes. The problem is exacerbated in moderate to heavy seas. The only way to ensure that you do not miss a target is to monitor the radar regularly. In fog, someone should have their nose literally planted on it.

If your boat is rolling or pitching quite a bit you'll need to pay extra attention to the unit. Returns may be intermittent. But you can still use them with great accuracy.

*There is absolutely no substitute for height of antenna.* Practically speaking, radar is a line of sight system, although Nonjy is incorrect in his characterization of radar waves which I'll explain further on. As for line of sight, a simple examination of Bowditch table 8 reveals that the horizon is 4.5 miles off from a height of eye of 15 feet. At 25 feet height of eye the horizon is now at 5.9 nautical miles, basically a mile and one half further that you can see an object at sea level. The furthest then that you would see another object 15 feet above sea level if you are at 15 feet above yourself is 9 miles, whereas for both at 25 feet it's 11.8 miles. That ain't chopped liver.

Remember also that it may be further yet because, instead of your eyes being employed, you're using radar which will see things smaller than your eyes may detect when hull down on the horizon. It's quite common to glance in the radar hood during the day and see a vessel some distance off, ie...hull down on the horizon, and then look in that direction and see her masts clearly. They were always there, just difficult to pick up by casual scanning of the horizon.

I've spent days on end rolling twenty to thirty degrees and the radar worked fine, if you knew how to operate it. And ship's radars are not gimballed. Mount your radar as high as may be practicable.

Now as to radar horizon. It's much easier to quote an expert than translate so I'll lean on the late Captain FJ Wylie, RN-ret., and the author of the seminal work, The Use of Radar at Sea, available from the Institute of Navigation. From the fourth edition, page 12...

"_The radar horizon._ If a straight line were drawn from a point at a given height above the sea, tangential to the Earth's surface, it's point of contact with the Earth would be the _geometrical horizon_ from the point of origin. Since light rays do not travel on straight lines but are slightly bent towards the Earth, the eye at the same height above the surface would see the _optical horizon_ at a somewhat greater distance; it would see slightly 'over the curve of the Earth.' With radio rays, the bending being greater, the horizon distance will be greater than in the optical case. With a standard atmosphere, which will be defined later, the _radar horizon_ for 3-cm. waves exceeds the optical horizon by about 6 per cent. and the geometric horizon by about 15 per cent. This is important because the sum of the radar horizon distances of the aerial and of a target defines the maximum possible distance from which that target can return an echo."

Even though the radar will "see" slightly further you can use Table 8 of Bowditch, Distance to the Horizon, to determine how far off you'll espy an object on radar, roughly. Add the height of your radar antenna and the height of the object above sea level together and enter Table 8 with that number. Thus, with your scanner at a height of 25 feet and the object at 100 feet above the water, you'll pick it up at 17.6 miles. the only thing that you can do to see further, under normal atmospheric conditions, is to mount the radar scanner higher or pick an object that is higher than the 100 feet.

I'll take exception to the notion as well that more power is wasted. there are many reasons to not opt for more power but lack of distance and clarity are not among them. You'll want more power in just those conditions when you need radar the most...punching through a rain squall, etc...

CD is incorrect in his point that the higher the antenna the more susceptible you are to false returns. Due to pitch and roll, you may have a slight increase in intermittent returns but not false returns. False returns are most commonly caused by sea state and the closer the scanner to the water the greater the number of false returns. It's far better as well to have an intermittent return from a higher antenna height than no return at all from a lower one.

I'll reinforce my statement on the desirability of longer range performance over close in performance to disagree with Dog and others while I agree with the poster formerly known as halekai. If you're using radar primarily to pick up a buoy or other craft a mile distant I would submit you are doing something wrong as a matter of seamanship. You've left locating either accurately way too late in the game. On the other hand, if you're picking up the Bungo Suido ferry, otherwise known as "Kamikaze Mike", there is no such thing as locating his high speed, I change course for nothing, ass at too great a distance.

One of the reasons MARPA seems little used is probably because sailboats move relatively slow. At 3-6 knots boat speed the relative motion track of a 20 knot ship is much closer to her true course and speed than were she also doing 3-6 knots. One should though develop a sense of relative motion which, in the absence of a reflection plotter on the radar screen can be done using a radar plotting sheet. Elsewise, it is way too easy to get into a "radar-assisted collision". The commonality of such events is why the Colregs deal with radar it's own self and the USCG conducts a completely different certification as "radar observer" from the rest of it's licensing testing.


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## Maine Sail (Jan 6, 2003)

Bene505 said:


> And somehow you collect beautiful sailboats too.


C'mon now I don't collect. I buy one, tweak it, get bored and move on.. A collector would still have all those boats.. I'm boat dumb but not that boat dumb!!:laugher

My wife once tried to count all the boats I've owned and I interrupted her and side tracked her with dinner a date. At dinner she started counting cars.. Better than boats I guess.

It's like the question every guy dreads hearing; "So how many women did you sleep with before me?"..... Ouch...!!

Don't ever let your wife try to count cars or boats if you're an addict like me...


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## Sequitur (Feb 13, 2007)

Long range radar is useful during landfalls in detecting mountain tops. I have made many landfalls this way on returns from Hawaii, Japan and the South Pacific.

My current radar is a Raymarine 2kw dome gimble-mounted 9.5 metres (31 feet) up the mast. So far it has performed beyond my expectations locally in a couple of stormy crossings of the Straits, several fog-bound passages and some night sailing.


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## Valiente (Jun 16, 2006)

Good advice here. May I add that MARPA does not appeal much to me, but that a separate AIS plot does. I think if RADAR is the best thing to happen to sailboat navigation, then AIS is a great compliment to RADAR.

Me, I've only used an old Kodan set with a CRT display on a steel sailboat, but I have been quite impressed with how a little instruction can greatly enhance the amount of information you can glean from radar. That Kodan radome was mounted on a mizzen about 15 feet off the deck, maybe 21 feet off the water.

Me, I would opt for a mast mount, because my mast can pivot in its tabernacle, meaning I can service it without a full dismasting or spending half a day in a bosun's chair. My question is the utility of a levelling mount over a fixed one. I too am waiting for more HD RADARs, as they seem to address a great number of questions (size, power draw and resolution).

I would recommend as a good research source this place: Panbo: The Marine Electronics Weblog Great little reviews and articles about all sorts of marine electronics, but the radar sets are very much going through big changes for recreational boaters.


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## Cruisingdad (Jul 21, 2006)

Maine Sail said:


> And based on personal experience with a self leveling unit and multiple boats with pole and spar mounts I can say that these theories all sound well and good until you put them into practice in the real word..
> 
> I said above I live and sail in foggy Maine. I have owned a Questus, regular pole mount systems and multiple mast mount domes. The Questus was converted by me from a fixed Edson pole.
> 
> ...


My experience is first hand and not based upon books or theory either. I do not quote it here unless I have seen it. I have used both too.

However, let me state that I think we "agree". If comparing a pole mount to a mast, you will never hear me say the pole mount is better. I also have mounted the last two on my boat on the mast. But I will also say that when we used a pole mount in the pacific, we got a suprisingly good distance out of it (it was leveled). That being said, I would still opt for the mast mount. But I feel that mounting it on top of your mast (to make a point) would cause more "intermittent" returns (to use Sway's terminology). Perhaps I used the wrong terminology - but the intent was the same.

And my experience is that you WILL, when pitching and rolling hard in a storm, get "intermittent" or "False" returns on the radar (whatever the right terminology is). But we agree Hal, mast mount is the best way to go... to a point.

- CD

PS What did you think of the 310? Is that a 310?


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## N0NJY (Oct 19, 2008)

> There is absolutely no substitute for height of antenna. Practically speaking, radar is a line of sight system, although Nonjy is incorrect in his characterization of radar waves which I'll explain further on. As for line of sight, a simple examination of Bowditch table 8 reveals that the horizon is 4.5 miles off from a height of eye of 15 feet. At 25 feet height of eye the horizon is now at 5.9 nautical miles, basically a mile and one half further that you can see an object at sea level. The furthest then that you would see another object 15 feet above sea level if you are at 15 feet above yourself is 9 miles, whereas for both at 25 feet it's 11.8 miles. That ain't chopped liver.


You said the same thing I said. You're applying height to the equation... something I didn't do. That doesn't make my statements incorrect 

In fact, it merely verifies what I said. If you stand on top of a tower, 25 feet up in the air above your boat you will have extended your viewing distance as well.

Radio waves, in particular radar waves DO travel in line of sight fashion. At higher frequencies (in the gighertz range) the signals simply do not "bend" and reflect back with any signal strength of consequence.

What it comes down to is nanovolts of energy that requires extremely sensitive equipment to pick up.

So... when it comes right down to it, the more expensive the radar unit, the more "sensitive" the receiver is, and the more powerful the transmitter must be to see anything reflected back "over the horizon".

There IS spreading of radio signals - thus some may "go over the horizon"... but folks you're talking about a sailboat, on the ocean and if you can't see something 35 miles out, chances are good you're NOT going to hit it.

I'll *give you* the "optical horizon" versus the "radio horizon", but the difference is fairly insignificant. Also, NOTE that the optical horizon changes based on the weather, whether there is a low pressure or high pressure system in the area, an inversion and your altitude above sea level (or for that matter whether you're AT the sea or on a flat, dry desert).

But again, FOR ALL intents and purposes (and by the way, I have a lot more radio experience than probably 99.99 percent of anyone on this board, including radar, and everything from ELF to SHF frequencies so I am not talkin' out my ass.....) the differences in "optical horizon on a clear day" and "radio horizon" are insignificant when it comes to the type and price of equipment.

(In other words, spending a lot more money on a system that doubles the power output of a radio transmitter is a DUMB IDEA)


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## N0NJY (Oct 19, 2008)

> And my experience is that you WILL, when pitching and rolling hard in a storm, get "intermittent" or "False" returns on the radar (whatever the right terminology is). But we agree Hal, mast mount is the best way to go... to a point.


The terminology is correct. "False returns".

BUT... note that this will mostly be CLOSE IN things, waves or whatever can return an echo. The "ground clutter" you see on radar displays is exactly this - false echoes from scattered radar signals. In fact a good portion isn't actually being returned from trees (some is) or whatever on the ground, but reflected off radio-reflective surfaces and bounced around.

In VHF and UHF radio... oh wait, better example. Anyone remember TV Rabbit Ears and "ghosts" on the television? THOSE are examples of "false echoes" where the same signal is being bounced around and arriving at the receiver slightly out of phase, which in turn causes fading, or apparently amplification of a signal (when it is IN phase).

Same thing can happen in radar signals especially on water. Large waves in the distance can return echoes too, in and out of phase giving you an indication of something that isn't really there, but appears to be.


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## Bene505 (Jul 31, 2008)

So what does everyone think about the upper radar on the "photoshopped" version of Sequitur's sailboat?


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## Bene505 (Jul 31, 2008)

That has to be another 30 feet up. Why not? 

Why only have a radar half way up the mast?

And since his jib doesn't go all the way up, it would be easier to tack without the jib hitting the radar mounting every time, right? 

By the way, the question is not academic for me, since I plan on installing a radar on our boat.


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## sailingdog (Mar 19, 2006)

Maine Sail-

That is impressive... what tweaks did you do to the unit and how much did it improve it from this untweaked image???


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## Maine Sail (Jan 6, 2003)

Cruisingdad said:


> But I feel that mounting it on top of your mast (to make a point) would cause more "intermittent" returns (to use Sway's terminology). Perhaps I used the wrong terminology - but the intent was the same.


In my experience and as Sway pointed out I'd much rather have an occasional false return or missed return on one revolution than NO return due to high seas as DOES happen if the dome is too low.

No one ever said to mount a dome at the top of a mast that is just dumb for a number of reasons. Yes there would be more effective pitch and roll the higher you go but also more distance.



Cruisingdad said:


> And my experience is that you WILL, when pitching and rolling hard in a storm, get "intermittent" or "False" returns on the radar (whatever the right terminology is). But we agree Hal, mast mount is the best way to go... to a point.


Of course you will! You'll also be worse off in a storm with big seas with a low pole type dome. My Questus made squats difference at "pole" level height, though I actually wanted it to after I'd spent soooo much money on it. If it had worked in real life, as it claims to on paper, I would buy one again in a heart beat as I take fog very, very seriously. I have been in seas with pole height domes where I could not get any decent returns due to wave heights that I would have with a spar mount even it they were every oteher rotation.

This is one reason I don't choose to use Marpa. The human interaction necessary to monitor targets is very important. If you loose a target for one or two rotations Marpa looses it, at least on the Raymarine and Garmin units I've used. arpa may have forgotten it but the human does not foget about it...

Again I have a pole mount currently and am not touting mast mounts because thats "what I use". I tout it because as you already know it works better and gives better range in more wide ranging conditions.



Cruisingdad said:


> PS What did you think of the 310? Is that a 310?


She was a decent value and Catalina was a very good company to deal with (if you van get to Frank). She really did not do well in rough weather though, much more fickle and fatiguing than our Catalina-36. She also had some bulkhead issues due to flex and construction techniques that made me nervous. She is a good bay coastal boat, as she is sold for. She is just not a 30+ knot open ocean boat. We opted for a boat with more robust construction this time around because we'd like to take four to five weeks soon to hit Nova Scotia again and I wanted a boat that I felt comfortable doing that in. I'd do in in a Catalina 36 but not the 310..


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## sailaway21 (Sep 4, 2006)

Nonjy,
I don't call a 6% increase over line of sight chopped liver. The Bowditch references were just given as examples. Radar can see somewhat over the horizon and that's all to the good, especially on a craft where your range is already compromised due to low antenna height.

CD,
I believe you're misstating something here that leads to yet more confusion. An "intermittent" signal is not necessarily a "false" signal! As the poster formerly known as halekai says, I'd rather have an intermittent signal than none at all. And, as Nonjy says, "false" signals are most commonly from sea clutter (leaving out his trees from sheer kindness on my part.  ) or rain clutter and those false signals are generally close aboard, ie...within five miles in rough weather.

Mainesail makes a very important point and one you should be aware of in your radar shopping when discussing MARPA systems. If you're tracking the _Globtik London_ in ballast those systems will do just fine. There's just something about 1300 feet of hull with 70 feet of freeboard that makes for an exceptionally fine radar return.  But the _Globtik London_ is generally not your problem radar wise. (And, if you get close enough she'll blot out the sky, seemingly!) I've worked with a great number of ARPA's on board ship and, while they are mandated by law, and they work OK in some instances, they are really nothing more than a convenience in that they save you the effort of resolving the speed/course triangle of relative motion. You do need to know how to do that resolution of that triangle for collision avoidance but, you don't need MARPA or any other automated system to do it.

The big downside to these systems and why they largely go unused in their automatic mode, versus the manual acquisition of target mode, is that they continuously pick up and lose targets that may either be real or false targets. They will drive you nuts with their lost target alarms and their habit of automatically tracking a wave while giving you a close CPA alarm. It's not at all unusual to acquire a target manually with one of these ARPA's, let it calculate course, speed, and CPA only to then manually delete the tracking of the target so as to not have to deal with the alarm when the system "loses" it for a time. You can do all the calculations necessary without the MARPA so I'm not at all sure I'd pay more for that system.

The dangerous aspect to those systems is that the operator may believe the engineer's hype and believe that his system will automatically acquire any threat to his vessel. Leading to a practice of turning it on and waiting until it squawks to look at the unit. That practice is highly unsafe.

I cannot tell you how much eye strain I've undergone in both foggy and rough weather conditions staring the whole watch at a CRT display gleaning whether I was observing a false signal or a sailboat echo. A submarine will show no lights submerged but at periscope depth and the only thing you'll pick up is a small intermittent echo off her periscope. If you're sailing off the approaches to Groton, Conn. or between Spain and the Balearic Islands, you'd be well advised to monitor those returns. But you must keep your nose in the unit in those conditions until you're sure that what you're seeing is a false return and not a small boat. It's, quite frankly, exhausting and stressful. You differentiate a false return from an intermittent return by it's location, it's frequency of return, and-most importantly-it's relative motion. A false return, say from sea return, will have amazingly the same course and speed you do...or be so erratic as to be almost instantly dismissible as only a false echo. A small intermittent return will show a course and speed, or move down the screen if dead in the water, and otherwise track like a normal target, albeit intermittent. But, if you do not track it in a systematic fashion you will incorrectly dismiss it as multiple false returns.

In my experience, I am always highly skeptical of any "automatic" systems involved in either shiphandling or navigation. Despite claims to the contrary by their manufacturers, they usually do not work as well at the margins as a system capable of being operated manually, where the operator and not a computer interprets the data received. I've seen it in radar, Loran A, Loran C, and autopilots. There is no substitute for the human involvement and interpretation. And the automatic systems need an operator whom is actually better trained than a manual system requires! He needs to know when not to trust the automatic system. The fellow with an older, less feature-packed, system knows that he must watch the radar every few minutes or so to stay abreast of things. Consequently, he doesn't get surprised by a target that snuck under the automatic acquisition device.

One last thing, that I'm sure Mainesail would agree with. If you cannot see the bow of your boat for the fog, you still need a lookout but it probably should not be you yourself. All you need is someone capable of saying, "Hey, look!" for that duty. Your eyes belong on the radar. What your lookout sees may already be doomed to hit you or will pass by safely; in either case, it's too late to do much about it. But your trained eyes on the radar will tell you well in advance that it's coming and your lookout will see or hear it pass safely down the side (hopefully). Don't put the rookie on the radar; dense fog is no place for training.


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## N0NJY (Oct 19, 2008)

I use trees because that's what I'm used to seeing  Not big ships.

The point remains... and my statements are ACCURATE.... that line of sight is just that. It's a term we use loosely in all radio systems to judge approximate distances for radio signals.

If you're in a plane traveling at 450 miles an hour at 30,000 feet, you can still see "all the way to the horizon" both optically as well as using radar. You CAN NOT SEE BEYOND THE HORIZON with any sort of equipment you, me or the OP is going to be able to afford to buy, without satellite assistance, without tapping into the US nuclear defensive systems and certainly not on a boat sitting at SEA LEVEL + or - 50 feet on a tower, mast or anything else.

You gain yourself a few miles, tops.

Another note, when I say "line of sight" I am not implying that "what you see is how far you can 'talk'" optically. I'm talking about from the point of view of an antenna radiation system.

Radars use high powered pulses of RF energy aimed through parabolic dishes to increase the effective radiated power of the system by hundreds of decibels (DB). This gives an APPARENT increase in energy in one direction.

The stronger the signal, the farther it goes to a POINT. That point is the tangential angle of the earths surface that puts the RF energy off into space - where it is going to hit NOTHING (therefore no return echo) except satellites and UFOs.... Beyond the horizon - whatever that happens to be given the height of your mast/tower/radar dish - you CAN SEE NOTHING.

No amount of power, antenna design, or resolution is going to increase your ability to see beyond that point.

That, folks is a fact.

Certainly quoting charts and graphs is a good idea and I'm not saying you're incorrect about the data.

But what I just posted is as accurate as any quotes, charts, graphs or mathematics that Nathaniel Bowditch might have conjured up in his time. 

And while he was certainly a very smart man and a credit to navigational theory - he didn't know squat about radar systems and I do.


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## Cruisingdad (Jul 21, 2006)

Maine Sail said:


> In my experience and as Sway pointed out I'd much rather have an occasional false return or missed return on one revolution than NO return due to high seas as DOES happen if the dome is too low.
> 
> No one ever said to mount a dome at the top of a mast that is just dumb for a number of reasons. Yes there would be more effective pitch and roll the higher you go but also more distance.
> 
> ...


We agree on EVERYTHING you said above. What would be interesting to know is in the conditions where your pole mount radar hit the sea face and was not effective, what the mast mount would have been like. I suspect it would have been "better", but in my experience, you would be fighting many false returns.

Now that this discussion/thread has been answered...

Regarding the 310, I agree. I personally think they could have beefed up a few things instead of saving a buck. But Frank and Gerry do not call me before they build a boat!!! I also agree about the 36. WIthout a doubt, one of the top boats they have built. THey discontinued that, as you know. Real bummer. But I bet the prices for the 36 level off nicely for current owners.  Same for the 380. They discontinued that too and replaced with that "387" thing. We have spent a LOT of time on the 36 and lived/cruised on a 380.

Regarding MARPA... I agree in general with what you are saying, but I can see no problem with using it. THe issue is if you "rely" on it, versus using it as another tool. There are places like SW Florida and Sea Lake Texas where there can be sooo much traffic, you cannot keep an eye on all of it. The MARPA could be handy in those situations. It is not meant to replace you, only help incase you miss something. Of course, as mentioned before, this part of what I am talking about is theoretical. I have it but have never used it (does that make me hypocritical?). If you have used it and say that it is worthless, than I guess my points are not valid as I have not used it in a real live setting before. I don't know. I may try it out on Lake Texoma and give you guys a quasi-real world experience.

Thanks,

- CD


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## sailaway21 (Sep 4, 2006)

Nonjy,
Your argument is with not Bowditch but with the late Captain FJ Wylie of Her Majesty's Royal Navy. And, tangentially, with marine radar operators everywhere. You can learn more here: Amazon.com: The Use of Radar at Sea: F.J. Wylie: Books


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## SVAuspicious (Oct 31, 2006)

On my previous boat I had a 2kW 18" dish Raymarine radar. On my current boat I have a 4kW 24" Raymarine radar. The improvement in resolution is quite clear. The ability to see weather coming in from further away is also clear. 

I have found MARPA to be a useful tool (not a magic bullet) offshore, on Chesapeake Bay, and on Delaware Bay. YMMV. I value the tool. For me, it frees me from the display and calculations and gives more time to focus on the real world around me. Again, YMMV.


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## N0NJY (Oct 19, 2008)

sailaway21 said:


> Nonjy,
> Your argument is with not Bowditch but with the late Captain FJ Wylie of Her Majesty's Royal Navy. And, tangentially, with marine radar operators everywhere. You can learn more here: Amazon.com: The Use of Radar at Sea: F.J. Wylie: Books


The charts are named for N. Bowditch. He was the mathematician who worked out what the basis of all of this is built upon.

But - I'll give you a separate example of why I'm arguing the point.

I am also strongly connected to something called "Skywarn". We do storm spotting for the National Weather Service, and I've taught electronics, radio theory, physics and even some astronomy. I know and understand things like "potential difference" and how static electricity "works".

I also understand, to a lesser degree how lightning 'works' (no one truly 'understands it, but I'm talking theory).

In practice, you will come across meteorologists who will use the terms "Positive and negative lightning" and honestly don't have a CLUE what the physics behind a lightning strike really is.

(You can ONLY have a negative energy exchange, that is a current flow from Negative TO Positive). With me so far? Bear with me just another minute.

When I questioned more than a dozen meteorologists on their use of the term above - they were completely dumbfounded as to why I was asking.

It is a "Terminology Issue". They are explaining things from a point of view of where the "negative charge" resides. Most don't really completely understand the theory of electron charge.

Thus when I explained the PHYSICS behind it they all went "OHHHHHHHHHH!"

They didn't change their terminology, but they no longer explain their ideas with the misconception that something IS, that really ISN'T

As to my "argument" (which it is not, it is a discussion) on theory...

I'm talking purely from an RF engineering (and PRACTICAL) point of view. I've put up more radio antennas and towers than probably everyone of the people on this site combined. I've tested and used radio systems, voice, digital, radar, repaired them, installed them, de-installed them, refurbished them - I've learned the theory over my 50+ years I've been around and started in the field when I was ten. I learned "the hard way" on some things and spent pretty much the rest of my life in school. I've been going to college for thirty years learning and re-learning things on radio and physics.

I'm not going to argue the point any further because it's going off topic based on the original question - but, I stand by my points, my theory and the facts.

RADAR WAVES travel in a straight line. Period. Once they are past the "radio horizon" if that's what you'd like to call it, they are gone, never to return. They don't bend, they don't hit things over the horizon and on consumer systems give you ANY indication there is something over that horizon.

I don't CARE what some manufacturer says about it. Physics is physics. 

No matter how much you boost the power (with the noted exception of bad weather full of fog) that power boost won't give you a return signal on the other side of the horizon.

Please note also - radar in fog works, albeit, not quite as well as everyone wants to think. The radar most of you use operates somewhere in the X-band.

X-band is around 7-12 gigahertz (GHz).

The wavelength of a radio wave at mid range (say, 10 Ghz for the sake of ... argument) is calculated by:

Lambda (wavelength) = C/Frequency

Where C is the speed of light (in some measurement, usually meters/second) and Frequency is in Hertz, wavelength. You will wind up with an answer that is someplace around 0.029979 meters. That's 2/100ths of a meter. Pretty small.

If you're in a pretty heavy downpour and can't see very far, understand that the wavelength of this particular group of frequencies is pretty close to the size of drops of water and you will scatter a LOT of energy (hence the need for MORE ENERGY in bad situations!)

This limits your range, and it limits your ability to see very far and certainly NOT as far as the "radio horizon" which just got vastly shorter.

My POINTs remain, radar is used in the dark, in places where you can't see visibly very well, and in bad weather. On a clear night with NO moon on the ocean - I doubt you can see more than a few hundred feet in front of you.

On a rainy day, you're not going to see very far, and in heavy weather, you might just need that radar.

For ALL practical PURPOSES radar serves it's purpose.

IF you're debating the exactitude of how well one works over another based on power factors, or resolution, the things I originally stated are STILL true.

You can't see over that "horizon".

(Now... let me contradict things somewhat - rf energy in those frequencies CAN be used to communicate well over the horizon using something called backscatter. Backscatter is the refraction of those waves by the troposphere - and area of the atmosphere that causes weather - thus clouds, fog, inversions can all have an effect. BUT the signal is still ONE WAY. It doesn't return, and that's required in a radar pulse. The record of backscatter communication is about 10,000 miles.)


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## Bene505 (Jul 31, 2008)

Maine Sail said:


> ...
> 
> This is one reason I don't choose to use Marpa. The human interaction necessary to monitor targets is very important. If you loose a target for one or two rotations Marpa looses it, at least on the Raymarine and Garmin units I've used. arpa may have forgotten it but the human does not foget about it...


Why can't they build a system that allows for a momentary loss of signal. This is not good design IMHO. Are there any manufacturers that don't have this problem?


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## Bene505 (Jul 31, 2008)

So I think we've determined that there is probably a few percent increase in radar distance over (clear day) optical distance.

What about the ultimate in height?

With modern antennas what they are, is there any downside to mounting an antenna way up the mast? Would you do it with a 24 inch, 4kw antenna?


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## GeorgeB (Dec 30, 2004)

This is a great thread! Reading it, I have come to two great realizations. First, I’ve become much too lazy in my radar operation. Time to crack open the manuals and spec sheets again. And second, Maine is one dangerous place – not only do you get pea soup fogs nine days out of ten, you have to dodge fifty knot ferries as they blindly careen through the waterways while keeping a lookout for kayaks and such, all the while doing radar approaches as GPS in the northeast is notoriously inaccurate. And did I mention the 20 foot seas and the perennial northeasters? Keep this up and pretty soon Smackdaddy will be migrating “down east” to partake in the excitement.

I’ll refrain from the more technical talk as I can’t remember those arcane specs like scan rates, beam angle, side lobes and the what not, but I would like to discuss the CONOPS side of the equation for a bit. I too, don’t use MARPA in the fully auto mode. I will manually mark and track any “contacts of interest”. These are mainly the tugs and barges that run in the Bay late at night as it is visually confusion with all the background lights to see what they are doing especially when they are maneuvering from pushing to towing a barge. Outside the Gate, I run in standby mode at the most as it is really easy to spot fishing boats visually even in swells. The only times I’ve painted a fishing boat up is when I suspected them of trawling and couldn’t figure out their course. I do use radar for collision avoidance in the fog and have shot radar approaches to both Half Moon and San Francisco Bays. I have been perfectly happy with the performance of my 2KW K band unit.

I use my AIS much more than my radar as it gives me much more useful data, it is easier to use and with my masthead antenna, greater range. Commercial shipping can transit the Bay at up to 20 knots and greater (we have high speed catamarans too). So I worry about these guys more. AIS not only gives me their speed and headings but also things like ship type, name destination, ETA, etc. This I very useful as I can easily figure out what terminal they are going to. This is so handy, I even use it in clear conditions and hardly ever listen to VTS anymore. AIS/MARPA was really useful racing to Hawaii this past summer as we were notified of any close approaches and one time even called a freighter one night on the VHF to arrange a crossing. The icing on the cake is the power consumption on the AIS was a fraction of what running a radar would be all night and IMHO worked much better. We never turned on our radar once during the entire crossing.


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## Valiente (Jun 16, 2006)

George, why is GPS in the U.S. Northeast "notoriously inaccurate"? I would assume that if you are tucked into something like a fjord that might be a problem getting sufficiently elevated "birds", but I have never heard that one mid-latitude locale was less covered with GPS signals than another.


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## GeorgeB (Dec 30, 2004)

V – Sorry, just my poor attempt at humor. I sometimes get the impression that “real” down east sailormen consider GPS and other modern conveniences as a sissy way of navigating. GPS should work well down east as it does here on the west coast. A lot of you guys like to do manual tracking of targets and I’d like to know how you do it. I installed my E system on the pedestal as I do a majority of my sailing either single or double handed with my spouse and wanted the convenience. However, when the wind and wave kicks up, I find it increasingly difficult to keep a close watch on the unit, especially when using the larger scales and that is why the automated functions appeal to me. When it gets difficult to steer I will even get a crewmate to stand beside me and have them “watch the scope”. Unfortunately, my wife treats all electronics like they are made of kryptonite. 

Another thing I don’t get is the concern about periscopes. You guys still have a u-boat problem there on the east coast? And you can pick out a scope with our little K band units? In a former life, I used to sell a lot of equipment to the USN and NATO just so the Big Bear couldn’t find them. Who would have thought that all they had to do was shop Funaro or Raymarine.


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## Bene505 (Jul 31, 2008)

GeorgeB said:


> V - Sorry, just my poor attempt at humor. I sometimes get the impression that "real" down east sailormen consider GPS and other modern conveniences as a sissy way of navigating. GPS should work well down east as it does here on the west coast. A lot of you guys like to do manual tracking of targets and I'd like to know how you do it. I installed my E system on the pedestal as I do a majority of my sailing either single or double handed with my spouse and wanted the convenience. However, when the wind and wave kicks up, I find it increasingly difficult to keep a close watch on the unit, especially when using the larger scales and that is why the automated functions appeal to me. When it gets difficult to steer I will even get a crewmate to stand beside me and have them "watch the scope". Unfortunately, my wife treats all electronics like they are made of kryptonite.
> 
> Another thing I don't get is the concern about periscopes. You guys still have a u-boat problem there on the east coast? And you can pick out a scope with our little K band units? In a former life, I used to sell a lot of equipment to the USN and NATO just so the Big Bear couldn't find them. Who would have thought that all they had to do was shop Funaro or Raymarine.


Maybe we need to keep our engine running or make other noise to let them know we are here. Kind of like the high pitched things you mount on your car hood to let the deer know you are coming. Maybe play the sound track to "Hunt For Red October" on underwater speakers. ..."Sir, for a moment there, I thought I heard singing".

Seriously though, it seems like something you can't control that would really ruin your day.

No takers yet on my "really high radar antenna" question?


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## Cruisingdad (Jul 21, 2006)

GeorgeB said:


> V - Sorry, just my poor attempt at humor. I sometimes get the impression that "real" down east sailormen consider GPS and other modern conveniences as a sissy way of navigating. GPS should work well down east as it does here on the west coast. A lot of you guys like to do manual tracking of targets and I'd like to know how you do it. I installed my E system on the pedestal as I do a majority of my sailing either single or double handed with my spouse and wanted the convenience. However, when the wind and wave kicks up, I find it increasingly difficult to keep a close watch on the unit, especially when using the larger scales and that is why the automated functions appeal to me. When it gets difficult to steer I will even get a crewmate to stand beside me and have them "watch the scope". Unfortunately, my wife treats all electronics like they are made of kryptonite.
> 
> Another thing I don't get is the concern about periscopes. You guys still have a u-boat problem there on the east coast? And you can pick out a scope with our little K band units? In a former life, I used to sell a lot of equipment to the USN and NATO just so the Big Bear couldn't find them. Who would have thought that all they had to do was shop Funaro or Raymarine.


George,

I wondered the same thing. Seems that subs would watch out for themselves as of their many "oops" lately. Being struck while partially submerged by a sailbaot will do little to get their captain promoted. I would think they know where you are long before you know where they are.

The exception is the tankers. Those guys go FAST. Once on your radar, they are on you within minutes. This makes shipping channels especially scary. However, my biggest use, as I have mentioned before, is the ICW and painting it at night. I use it at the 1/4 to 1/2 km setting - and it has saved my bacon many times.

In general, I can see where everyone would have a different use depending on their location. I still would choose radar over a Chart Plotter on my required equipment!!

- CD


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## GeorgeB (Dec 30, 2004)

Back in my old crow days, there was a saying. “He, who illuminates first, dies.” Things like sonar and radar were kept off in favor of hydrophones and ESM. The problem is sailboats don’t have much of an acoustic signature with the engine off. However, subs can recognize the splash of a sonabuoy so go figure. Speed of large commercial shipping is one of the reasons why I like my AIS. That, and knowing where the edge of the shipping channel is too. One year (pre E System) we were coming out of the delta near a particular nasty area known as middle ground. Combination of river current and an ebb flowing against a 20kt wind on the nose made for some steep, nasty chop. Real “Victory at Sea” conditions. Smashing through some waves and flying over others we were hanging on with all of our attention facing forward. At one point I sensed approaching darkness out of my peripheral vision, only to turn around and see the bow of a Korean Freighter looming above us. Fortunately, we were on the edge of the very narrow channel and they slipped by without a problem or warning horn, just a smile and a wave from the sailor standing watch on the bow.


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## Bene505 (Jul 31, 2008)

So how far up the mast can you go with your radar antenna? Can you way up?


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## billyruffn (Sep 21, 2004)

sailaway21 said:


> I cannot tell you how much eye strain I've undergone in both foggy and rough weather conditions staring the whole watch at a CRT display gleaning whether I was observing a false signal or a sailboat echo.......
> 
> You differentiate a false return from an intermittent return by it's location, it's frequency of return, and-most importantly-it's relative motion. A false return, say from sea return, will have amazingly the same course and speed you do...or be so erratic as to be almost instantly dismissible as only a false echo. A small intermittent return will show a course and speed, or move down the screen if dead in the water, and otherwise track like a normal target, albeit intermittent. But, if you do not track it in a systematic fashion you will incorrectly dismiss it as multiple false returns.
> 
> ...


I culled the above from Sway's earlier post because there's a lot of wisdom there, and I was concerned that, in all the talk of wave lengths, wattage, frequencies, ranges, etc, his key point was getting lost in the "clutter". At the end of the night landfall or a day of piloting along arocky shore in dense fog, it's really not the equipment that gets you there safely -- its the operator.

If you don't take the time to learn what you need to know about operating the unit and spend lots of hours in good visibility learning what it's showing you....and when it's dark and foggy, if you don't, as Sway says, "keep your eyes in the radar" with your brain in high gear.... then even the best, top-end, high-power, 72-nm, fully-automated, mast-head mounted radar won't do you much good.

Billy Ruff'n has a basic Furuno unit with a 16 mile range and early 90's technology. No bells, very few whistles. Works great -- I see the big boys at 18 miles or so (yes, it can see beyond it's advertised range with a target on the bow), which is plenty of time to get out of their way. We can see the little guys when they get in a bit closer, but in the fog, we slow down so we have plenty of time to get out of their way, too. If our radar failed tomorrow, I'd try to find another one just like it.

I think we'd all learn a lot from a thread on operator technique -- Sway starts down that track in his post. I'd encourage him to expand on it either here or in a new thread.


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## Valiente (Jun 16, 2006)

I agree. As I said earlier or elsewhere, my only experience with "live radar at night" has been with an old Kodan unit with a monochrome CRT about seven inches across...but I have had a chance to fiddle with the knobs while being instructed and it's quite amazing how much useful detail you can achieve in such "basic/primitive" units, and, perhaps more importantly, how much extraneous or useless detail you can suppress or distinguish as "safe to ignore".

Having had some experience with SW and CB rigs back in the '70s as a teenager, the experience of exploratory tweaking was not scary to me. It revealed that RADAR sets are quite subtle devices, capable of many more tricks than seeing hard things at varying distances.

These days, I wonder very much if our "sensory extension devices", like RADAR, are _too_ good in the sense that they provide a great deal of information, not all of which is necessary and some of which is bound to be confusing. The range and power issues, with its assumption that farther range is better and greater power yields better coverage, are part of those problems. It's like having a sports car capable of 160 mph in sixth gear; which means it's driven in second gear in city traffic most of the time.

The "too much info" issue is compounded, or can be, I think, by the multi-function displays. I like plotters and I like stand-alone radars, and I think if I can't superimpose their information in my head, I need more training or need to consult a paper chart.


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## Bene505 (Jul 31, 2008)

Very good posts here. The Mark 1 eyeball, with the Grey Matter 5000 behind it, paying careful attention to even the oldest reliable radar goes a long way.

I can't wait to get my radar. and get it installed. (And I'll probably play with it even before it's installed.)

So far I haven't heard too much against putting it high up in the mast. Maybe the new 18" Garmin (the one with 4kW) would be small enough to justify putting it a little higher up. But if I'm doing all that, I'd love to have the extra resolution from a 24".

I just have to figure out how to keep the jib and spinnaker from getting stuck on it. (And I'd have to redo a bunch of things to put it on the very top, so that may not be the way to go.) I know, I know, I have to envision what I want and then make it happen, right?


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## Rockter (Sep 11, 2006)

Bene :

I bought this base-model radar...

JRC Radar 1000

...about 10 years ago after running into fog one night on the approach to Inverness. It was just to avoid being blind like that again.

It is about 12 ft above the deck on a pole, and it works passably, giving enough warning if someone is going to run into you. Paradoxically, fog often equated with flat calm here, and it becomes very sensitive for a wee radar. I have detected a lobster buoy at about 4 miles. Larger vessels are easier to see.

I have had trouble aligning it and it is still out of alignment.

In hindsight, I would buy the next model up.


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## Kick (Nov 21, 2008)

Thanks Rockter. I'm thinking about a Raymarine, since the autopilot and speed/depth are Raymarine. They may connect in some way, maybe not. Raymarine has a nice system where you cannect many things into the GPS map. Garmin has this too and I think the others must also.

My general policy is to let others buy the Nimbus 5000 (top end model) and buy whatever it was they got rid of when they did. That way I get good capability for a good price. So while everyone else is getting a 12", I'll stick to the 8" or even 7", for a fraction of the price. Going too old or too low in capability has drawbacks going forward. Instead you may be happily surprised down the road that there's a capability included that you'd like to have. Also, installation cost/effort being what it is, it make sense to not go too far down the purchase price curve IMHO.

That all said, I'm sorely tempted to get the best I can here, since it seems so useful and safety enhancing, kind of like buying the best PFD you can afford.


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## goboatingnow (Oct 10, 2008)

couple of things from the posts and my experiences with my own setup and as a result of doing sailboat deliveries

(a) Height
There is a compromise between height and performance. firstly too high and the vertical beamwidth will lead to blank spots close in, especially at high angles of heel, secondly the scanner will experience higher acceralation forces high up and that leads to wear

So mid mounted is why most are where they are. Having experienced both pole and mast mounted systems mast is better, and forget the self levelling systems.

(b) Power, range and beam width.
The defining characteristic is horizontal beam width , that is what produces the goods. a 2kw 4k etc makes little difference. but if you compare the average 18" radome with 5 degress or more of horz resolution to one with 1.6 degress for example the resulting picture is like night and day, Always fit the best horizontal beamwidth your budget allows

(c) Marpa and heading sensors

Firstly the heading sensor in the Raymarine autopilot will give your system a heading feed, It will however be compete sh1t. This is what gives small boat marpa a bad name. You need to invest in the best heading sensor you can find to make the Marpa funtion rock solid, most "lost marpa locks" are caused by your boat yawing and the heading sensor/processing time delay not keeping up. MARPA simply works by essentially tracking the pixels on the screen within a defined "search" area of pixels. If they move rapidy away or disapear and reappear a little aways, MARPA system tend to loose lock. The quality of the heading sensor, ie its update speed, is paramount. In reality I found that only the GPS based heading units really lock MARPA down. On large ships the yaw is comparitively tiny and hence there ARPA is quite good.

(d) MARPA and the navigator

I absolutly agree with the negative comments I'm a electronics engineer and I love gadgets, I've yet to see a small boat MARPA system ( other then my own ) be actually useful at sea, constant lost lock alarms, invalid close contact alarms, just serve to frigthen the daylights out of the crew and in all cases I just end up turning it off. ( theres nothing worse then a Raymaine E120 bleeping madly while your staring through the bins looking for the goddammed light aspect. WIth a $$$$ setup it can be made to work quite well, but.....

I disagree that big ships arnt the problem,sure the radar sees them but today this damm monsters are travelling at over 20 knots on the high seas, it can give you less then 5 minutes to work out what the hell is going to happen. advance warning of big ships is what its all about ( thats why AIS will be huge). I dont really worrying about other sailboats and the like.

The big problem today is that average joeboater goes to boat shows and sees all this high tech geez whizz gear and slick salesmen explain how it all in theory works. What said slicksalesman doesnt explain is the real world issues the bugs and problems etc ( when I first had my E120, it had the night mode backlight bug, turning down the night mode caused the unit to blank the screen , usually just when I really needed it and teh damm thing runs UNIX!. so the reboots are slow... ( by the way furunos new Navnat 3D units are headless Windows XP. ( lets rerun the Windows joke about if windows ran your car....!)


Similarily HD, and SHD and UHD etc systems look great, but they are really only post processed images from a conventional radar scanner. Treadcarefully

There is a huge danger that these integrated systems with 3D virtual views, overlaid with Marpa and AIS etc will be taken as if thats whats really out there, What really gets my goat is people using 3D bathymetric views to nav the boat as if thats actually what the seabed looks like....! Navigation is not grand theft auto

As I say to people , dont forget "keep looking out of the window"


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## xort (Aug 4, 2006)

darn good discussion
what about power draw? comments on the tradeoff of power vs power consumption? an all night sail with the radar & plotter on can eat a battery bank pretty fast. what kind of differences in power draw with the various models?


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## Bene505 (Jul 31, 2008)

Another excellent post!!

To bet horizontal beamwidth you need a larger antenna, right? How do you get anything more than 24 inches mounted up on a mast. It seem impossible, unless you only use a storm jib. Any ideas?


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## Rockter (Sep 11, 2006)

I find that it is rarely used. 

It is very good for telling you how far off a shore you are at nght. A shoreline stands out well.

Last time we used it was on a Loch Ness sail, at night, in the rain. It certainly keeps the boat in mid channel.


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## sailaway21 (Sep 4, 2006)

It's not that large ships yaw less than boats...it's that they use a gyro compass for heading input to the radar, steering stand, etc...

Ship's ARPA's drop "targets" all the time also, for a variety of reasons. As I've said before, the automatic nature of the system is nothing more than a salesman's pitch. 99% of use aboard ship is done by manually selecting and deselecting the target one wishes to track.

Val and goboat bring up some good points that provoke some of my Luddite memories that I've somehow failed to shed. Mind you, some things have improved. When I first went to sea, the Mark 14 Gyro compass was the norm and it had it's own room on board ship. It was the size of a big block Chevy motor and needed about the same level of maintenance. Today's gyros will fit within a cupboard and are zero maintenance.

An example of feature-mania and "modern" design. Back in the late eighties Sperry came out with the new generation steering stand. For years immemorial Sperry dominated the gyro and the steering stand markets for commercial and naval ships. They had their quirks but reliability was not one of them. In any event, the latest steering stand did away with the old "you can find it in the dark by feel" knobs and levers we'd known so well and replaced them with an LED illuminated touch screen pad. It was also able to be integrated with the satellite navigation system. No, not that navsat, the original navsat, the Navy Transit system. Also gone were the manual steering dampeners for rudder rate and yaw allowed. That would be done now by an adaptive computer within the steering stand. (You can probably see where this is going!)

First off the link to the satnav never worked much at all. The ship would just change course at will for no valid reason and the stand was designed for regular inputs from the satnav which the Transit system didn't always deliver. Every mate, on every ship, spent about two four hour watches trying to make the thing work and then never bothered with it again. The Sperry engineers would look at it and pronounce it just fine, which it probably was; in Garden City, Long Island.

The adaptive steering aspect of the system was a less than unqualified success as well. It worked fine if you had it on at all times and never left the open sea, as in going from benign conditions into steadily worsening ones. Ultimately, in heavy weather, it tried to oversteer and you couldn't dampen it out so as to just let the ship have her head...similar to the way you steer your sailboat following a compass course. The biggest problem with that deficiency was when the ship left port and got into weather immediately. You were stuck with using hand steering because the ship was already moving so much the adaptive function couldn't update itself or adapt before getting blown completely off course. That didn't make the AB's very happy, I can tell you...hand steering gets old on board ship also.

The coup de grace though was that touch screen LED lit panel, the one that ran everything. The panel itself, thank god, was rock solid reliable. The illumination was another story. If that went out you had to buy a whole new $600 touch screen panel. Shipping companies are not in the habit of carrying expensive, other-than-necessary, spares so whenever you wanted to switch from hand steering to the "Iron Mike" at night the AB on the wheel had to get out his flashlight and fumble around with the buttons. And that's another thing, the old steering stands had a knob that was oblong in shape, which you used to switch from the iron mike to hand electric steering. The knob was large and the only one of it's shape on the stand. If for some reason you suddenly needed to want the ship on hand steering for a possible course change for a pesky sailboat, the AB just reached down and switched over by feel alone. Total time from, "Put her in hand and come Hard Right!" was maybe five seconds max. before the rudder started to swing. With that goofy touch pad, either with or without the LEDs burned out, it took the AB five seconds to say, "Let's see" as he gazed at the buttons or got his flashlight out. They got better with time and eventually somebody put a wad of epoxy goop or something over the pad for, "Hand" so you could feel it.

But the lights were another issue. Once upon a time ships used a certain bayonet bulb for instrument illumination; looked like a small Christmas tree light. You could get them in any color you wanted but a good Second Mate always had a bottle of carmine red nail polish squirreled away in case you ran out of the red ones. The engine room only had white ones so we could scrounge one off a snipe and paint it. The bulbs all ran off a rheostat for dimming. And everything used the same bulb; the gyro four decks down, the repeater stands on the bridge wings, the steering stand, the chronometer box, anything iwth a night light used that bulb. I cannot believe I've forgotten the GE number for it! If for some reason you ran out of spares you could steal one from a less critical application. And you could change them in the dark with just a quarter turn of the cover/light diffuser, twist out the old and in with the new. I think they were a buck a bulb. Instead, with the new and improved steering stand, you might go a voyage and a half or so waiting on a new panel. Usually one that had been redesigned for some reason but not for the reason of illumination because the new panel's lighting would fail approximately six hours after installation with Ambrose Light five miles astern!

So you see why I view a lot of this stuff with a jaundiced eye. I feel the same way about radar overlays on chartplotters. You're complicating something that doesn't need to be complicated. Every additional integration is an additional failure point. And, when you start cramming every bit of data conceivable onto one screen you increase the possibility for confusion, not to mention paying attention to data that is irrelevant to the detriment of important data. goboat said it well when he said this isn't "Grand Theft Auto"!

Were I looking for a radar unit, I'd want the one that let me adjust and tweak as many parameters as possible, by hand. There's no such thing as automatic, although there is automatic failure. Especially in heavy weather, I'd spend the whole four hour watch adjusting and readjusting my radar set. Too much clutter adjustment and you might miss a sailboat or a sub periscope; they show up about the same on radar. Too little clutter and you white out the center of your screen. Same thing with the gain; up and down all night.

As to the humour regarding submarine periscopes: I got paid too much to collide with a submarine popping up for a quick look around. A shipmate had one come up to periscope depth on him right in the Strait of Gibraltar. Came up right under the ship! (Long story I've told elsewhere...the US Navy denied and then paid!) Short story on subs and the Navy in general; you make a grave error if you think anything like, "with all that technology they surely see" or care about me. I've been at the controls of an old Raytheon 3cm radar unit while our ship was refueling at sea, four abreast. Good unit that old Raytheon 3cm. I picked up what turned out to be a sailboat in the hazy Mediterranean afternoon and identified him visually one point on the port bow. The Master called over to the aircraft carrier alongside and asked them what they wanted to do about this sailboat now five miles off? (You're only doing thirteen knots when refueling at sea.) Their response, with all the technology and manpower on three separate warships was, "what sailboat?". I'd like to think the sailboat was glad there was a merchant marine officer or two on those ships! Ironically, this was just after some Lieutenant told me how they were tracking the _Kirov_ or some such Russian warship that was 100 miles away. If that sailboat had been a submarine laying dead in the water, and we'd been at war, she'd of had us all!


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## Bene505 (Jul 31, 2008)

Sailaway -- Awesome post and experiences from someone who really knows how to use a radar. Thanks! 

Do the modern units let you adjust the gain and the other things that you need to adjust/tweak as you go?


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## goboatingnow (Oct 10, 2008)

> Do the modern units let you adjust the gain and the other things that you need to adjust/tweak as you go?


yes they do



> To bet horizontal beamwidth you need a larger antenna, right? How do you get anything more than 24 inches mounted up on a mast. It seem impossible, unless you only use a storm jib. Any ideas?


If you mast is big enough its common to mount it protected by two concentric stainless guards, one above and the other below the mount. The genoa brushs against it as it goes through.



> I find that it is rarely used.


 do you mean youdont use it at night , at sea its the most used piece of kit at night, crossing the atlantic I used it regulary to track squalls.

While Sailaways post brings awry smile to my face , I dont quite share his level of pessimim about modern electronics. ( and being a ex electronics engineer you would expect that). The fact is that electronics can be made to survive in conditons that all human life would have expired by. However they also get built to a price point as well.

In practice modern systems if installed properly and protected from battery spikes etc will work reliably. Nor do I share his concerns aboyt chrtplotters overlays with radar. The game has moved on, you can have two networked units and bring radar on one or charts on the other. in practice I agree with him in that at sea away from coastal pilotage . I rarely use the plotter except maybe once per watch. The dedicated radar is one most used and I would regulary power it out of standby and check for traffic and squalls. Once I detect traffic I leave it on and actually run simplifed plotting just using my fingers to act as vectors to give me true course.

I have been on ships with recent modern IMO certified ARPA units and they are orders of magnitude better then the lesiure ones.

Ps\ as to submarines, I had one surface about 100 feet away or so it seemed near the straits of gibralter, it had a yellow flashing light and on seeing it rise out of the water, your brain kinda does a homer simpson moment

and I also sailed into the middle of a carrier battle group at night that was running with no lights, Thats was some wakeup when I finally got a VHF call.


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## Valiente (Jun 16, 2006)

I just like the idea of a robust, dedicated radar display that can *optionally* feed to a laptop chartplotter (I have a pilothouse cutter, and so have the luxury of navigating out of the weather when I don't need to handle sails at the outside helm).

This is because of the "single point of failure" issue.

It is literally cheaper (by far) to carry five or six old laptops (early P4s are about $250 each with decent 14 inch screens), with "ghosted/imaged" hard drives, identical power supplies, etc., packed away with dessicant and bubble wrap for safety, and to use those _in conjunction_ with radar, AP, fluxgate compass, etc. Even a handheld GPS can take an external antenna and can feed lat/lon. to a plotter, and you should have the paper chart for any likely harbour approaches and/or reefs or island in your way anyway.

I can see why people love the multifunction units. I can also see why they could either break down, leaving you scrambling for a hand compass and the binoculars and praying you can find that old GPS stuffed into the chart table, or conversely, that their embarrassment of informational riches could cause you to miss a critical fact or to blithely stand into danger.

Strictly anecdotally, the last ten years have seen both the increase in sailors making predicable landfalls at predicted times, and the increase in perfectly functioning boats in non-heavy weather running into clearly marked obstacles or aground. Or into sea walls and jetties and beaches, for that matter. At top speed.

I don't think the two examples are unrelated.


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## Bene505 (Jul 31, 2008)

Valiente said:


> I just like the idea of a robust, dedicated radar display that can *optionally* feed to a laptop chartplotter (I have a pilothouse cutter, and so have the luxury of navigating out of the weather when I don't need to handle sails at the outside helm).
> 
> This is because of the "single point of failure" issue.
> 
> ...


Valiente, good point. I always figured it was a sleeping/inattentive crew with a GPS autopilot set for the harbor entrance. The autopilot dutifully put the boat right where the crew set it to go, within the accuracy of the unit. Maybe we should google "failed MFD" and see what the hits are.


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## Valiente (Jun 16, 2006)

I couldn't say. All I know is that I was pulled over in the thick fog once in Toronto Harbour by the marine police because they wanted to know who was bothering to keep a proper bow watch with the proper sound signal....yeah...actually doing the seamanlike thing sticks out like a sore thumb!

Me, I was plotting my course by paper chart to creep my way from buoy to buoy in order to get to the marina with the cheapest diesel!


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## jackdale (Dec 1, 2008)

Cruisingdad said:


> George,
> 
> I wondered the same thing. Seems that subs would watch out for themselves as of their many "oops" lately. Being struck while partially submerged by a sailbaot will do little to get their captain promoted. I would think they know where you are long before you know where they are.
> 
> ...


I agree about radar being my choice if forced to make the choice. The chartplotter does not show other vessels. Racons are more useful on radar than chartplotters.

I generally sail on a boat with a networked E series Raymarine.

I sail a lot at night and in fog using MARPA as another tool. Yes, we get false targets and lose targets, but it sure beats seeing nothing.

I have not yet used AIS, but I would like to see it in action. Some of the AIS web sites are intriguing.

Jack


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## Sequitur (Feb 13, 2007)

jackdale said:


> I have not yet used AIS, but I would like to see it in action. Some of the AIS web sites are intriguing.


AIS is a wonderful tool for me. With all the commercial traffic here from Alaska cruise ships, bulk carriers and container ships to tugs and barges, log booms and ferries, the waters are nearly always busy. Heading out from Vancouver entails crossing traffic separation schemes, ferry routes and tug and tow routes, and my AIS allows me to know what course and speed the various vessels are making, what their CPA is and often what their destination is.

Knowing a ship's destination allows me to predict its movements and to act accordingly. For instance, a north-bound container ship indicating its destination as Roberts Bank can be reasonably expected to slow and alter to starboard well before we get into a crossing situation. I can relax and continue on my course, watching for his move, and acting only if it doesn't come. Previously, without AIS, I would have altered early to pass under his stern only to find him obviating my move a while later with his alteration.


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