# Stupid racing question - Navigation



## jarcher (Jul 29, 2008)

This question is going to reveal just how little I know about racing big boats, so apologies in advance.

I have been reading about interesting instruments systems that provide target boat speed data to the crew. As a software guy I find this intriguing, and I understand how the computer combines all the data to produce target boat speed data and the best course to sail to a downwind mark.

What I don't see is how it knows where you are going. Of course if the crew knows this then they can tell the machines. And I suppose if the race uses well known navigation aids as marks that's easy to do.

But, in the case of a race where the marks have been dropped in place for that race, how does the crew get the mark location information into their computers?

More to the point, someone mentioned that I won't be able to see the marks, so I should "just follow all the other boats." Well we all know the flaws in that strategy! So then, how does the crew know where the marks are, just to get to them?

Thanks...


----------



## zz4gta (Aug 15, 2007)

They'll usually give you a bearing and distance from the previous mark or starting line if its a drop mark course. Check your SI's.


----------



## DrB (Mar 29, 2007)

*zzrgta is correct*

There are at least two methods that are used to define a course. The method that zzrgta has stated where the committee boat has at or very near the start line and on the boat the post the wind/course bearing from the committee boat and the distance.

The other method that is sometimes used is to use two government marks as the course. Mark 1 is one half of the start line (the committee boat or a drop mark is the other) and the turning mark another gov mark. If your sailing in the same waters each week (weekly race), they sometimes print a chart and label each mark with a letter or or some other designation that distinguishes it from the other nearby marks. On the committee boat, the post the mark labels on a panel before the start of the race You pull out your chart with the mark labels and determine the course.

If there is a course change during the race, and it is a multleg race, they put up flag and post the new course.

DrB


----------



## jarcher (Jul 29, 2008)

zz4gta said:


> They'll usually give you a bearing and distance from the previous mark or starting line if its a drop mark course. Check your SI's.


Ah, so they just tell you. Makes sense, thanks!


----------



## jarcher (Jul 29, 2008)

DrB said:


> If your sailing in the same waters each week (weekly race), they sometimes print a chart and label each mark with a letter or or some other designation that distinguishes it from the other nearby marks. On the committee boat, the post the mark labels on a panel before the start of the race You pull out your chart with the mark labels and determine the course.


Yeah this is how we did it years ago for dinghy club racing, thanks!


----------



## AdamLein (Nov 6, 2007)

Around here there are two yacht clubs that use the same set of marks. Two of them are permanent government marks, the other four are dropped by the race committee in more or less standard locations; the sailing instructions contain lat/lon coordinates of these locations, and they are depicted on a little photocopied chart. Also, you get used to the locations pretty quickly. However I would agree that it's still difficult to see the next mark right away, but with a couple of crew members looking out for it we usually spot it quickly.


----------



## CLucas (Feb 10, 2007)

If the course is a combination of govt and club marks, set them as waypoints in your GPS prior to race day. I do this with a handheld Garmin and make it somebody's responsibility to navigate to the next mark/waypoint after rounding each mark. Using the "compass" view on the GPS, we have a clear bearing and distance indication to each mark to help keep us on track, regardless of weather or conditions. Chances are the club marks are set at approximately the same coords (probably checked by GPS).

Good luck and have fun.


----------



## tommays (Sep 9, 2008)

Well its sure NOT anything new as Flyer had the first full systems allmost 30 years ago in the Whitbread (Now Volvo race)

Many basic handhelds give a VMG readout if you know were your going 

We have and Ockam system and you dont want to know thats it worth about 25k BUT it does not really matter were you need to get it takes wind speed ,dirrection ,boat dirrection ect and if you want to add another module give a % of what you should be doing 


We pretty much wing it and use the knotmeter as the Ockam cant really figure out the current and other boats


----------



## roygrady (May 27, 2009)

25k? wow!


----------



## jarcher (Jul 29, 2008)

tommays said:


> Well its sure NOT anything new as Flyer had the first full systems allmost 30 years ago in the Whitbread (Now Volvo race)
> 
> Many basic handhelds give a VMG readout if you know were your going
> 
> ...


So you have $25,000 worth of instruments in the best system available and all you use is the boatspeed indicator? I'll offer a favor; I'll be happy to take the rest of the system off your hands. I'll come and collect the stuff, and only charge a small, discounted rate for my time 

I am building up a Nexus system which is quite nice. I selected it because I already had a server and log and depth transducers that came with the boat, and I am adding compass and wind transducers. I am more interested in getting true wind direction then VMG.

But I was wondering how to find the marks, regardless of the instrument package. If the RC provides distance and bearing for set marks or otherwise tells us ahead of time what the marks are it's easy.

I mostly raced dinghys so you could generally see the marks.


----------



## tommays (Sep 9, 2008)

Well

We use ALL the instruments BUT there NOT the be all to end all 

VMG is the king of info BUT there is a lot of boat traffic to deal with and staying between them and the finish line is the real goal 


1. We own a very good current book of Long Island Sound and the harbor we race in 

Knowing how a significant current is going to affect your position is just NOT something instruments can help with at this price level  

2. You can buy a crazy starting line system which is still NOT going to stop you from putting yourself in a bad starting position 


3. There is just basic stuff like the long term odds favor sticking to the middle unless there is something out the norm


----------



## jarcher (Jul 29, 2008)

Haha yeah I know that instruments don't win races. I just couldn't resist a little poke about your knot meter comment.

BTW, many people would disagree that sailing to VMG is the best approach. Ockam considered not including that info in their displays, but bowed to marketing pressure to do so. 

I see you mention a J24 in your sig, do you have polars for it? Do you let the instrument package generate target data for you? 

To get Nexus to do that you need the newer FDX server and a PC, which I don't have. Maybe next season, since the FDX server upgrade would cost $800, the polar data would cost about $350 and then there is a PC, although I could bring my laptop. All this for a 32 year old boat :laugher


----------



## tommays (Sep 9, 2008)

I have a sailcomp and a windex on the J24 and NO knotmeter 









I DON'T use the tack buttons on the sailcomp









And just and a really OLD GPS for R&B with NO VMG


----------



## jarcher (Jul 29, 2008)

Ah so i guess it's not the J24 with the Ockam package.


----------



## bheintz (Jun 14, 2001)

There is a lot of really good racing navigation software, but it's only as good as it's calibration.

Primarily Compass Heading is most useful. Next Boatspeed (which can be gauged by your speed with the competition.) If on the Chesapeake, Depth is vital. Next, in order of priority, is True Wind Speed and Direction (the final solution between Bs, Hdg, AWS, and AWA). On a separate GPS we watch Range, Bearing, Speed Over Ground, and Tracking (Course Made Good). 

The Ockam system that Tommays mentioned can also give Set-and-Drift, Favored-End-Of-The-Starting-Line, Distance-To-Layline and a host of other useful goodies.

I'm still holding out for the Seat-of-the-Pants and Gut-Feeling indicators.


----------



## tommays (Sep 9, 2008)

No Zzzooom has the system ,it had a rich PO in its early like who did a RIG,rudder, and Two keels till he got it right along with the instruments


----------



## jarcher (Jul 29, 2008)

tommays said:


> No Zzzooom has the system ,it had a rich PO in its early like who did a RIG,rudder, and Two keels till he got it right along with the instruments


That PO would have had to be pretty wealthy to foot the bill for all that. What kind of boat is it? And yeah, the Ockam stuff is pretty cool. Getting boat speed and true wind data is mostly what I am after, but it would be nice to get target boat speed. Maybe when I am rich


----------



## jarcher (Jul 29, 2008)

One point for anyone reading down the line, VMG (velocity made good) on a sailboat should be thought of as progress directly into or away from the wind. If the true wiind is 90 degrees off your bow, VMG is zeri. Progress toward a waypoint is SOA (speed of advance) and not really VMG.

As such, a GPS can not really tell you that. For this, you need an aparent wind angle/speed transducer, a log (speed through water) transducer and a compass transducer (or a GPS providing bearing data, but the compass is better). Or at least you need all that data and a pocket caculator.


----------



## tommays (Sep 9, 2008)

Zzzooom is a 1970 C&C 35 and the PO hired Britton Chance to do his naval architect thing on the boat to about 100k


It was Campaigned big time and became a mess when he moved onto other things

The current owner allways liked the boat and bought it back to life DIY while racing it over many years now 


VMG is progress to your mark and exactly what a GPS tells you If it has that feature which many handhelds DO


----------



## jarcher (Jul 29, 2008)

Well VMG to mark vs VMG to the wind are referred to differently in different places. Here is one example:



> To avoid the problem with VMG to the mark, we can instead use a different type of VMG that measures net speed (directly) into the wind, called VMG upwind, rather than net speed toward the mark. In the diagram at the left (VMG Upwind), boats A and B are in the same positions as in the prior diagram (VMG to Windward Mark), but both have the same VMG upwind (solid arrows) since both are on the optimum pointing angle, traveling through the water at the same speed.


Why VMG Matters - a knol by John Navas

Ockam and Nexus both use VMG to mean directly into or against the wind, and I have found that this is common when referring to racing.


----------



## tommays (Sep 9, 2008)

It is chicken and egg 

It depends on the GPS as the new ones do it different and dont require a costly system

The S10 calculates the heading from the downwind reference point to the upwind reference point. This heading is assumed to be the wind direction. Since the only information derived from the reference points is this heading, the position of the reference points in absolute terms does not matter. The only thing that matters is the position of the upwind point relative to the position of the downwind point.
The S10 takes GPS readings every second to get your actual speed as well as the heading of your course. The device then multiplies your speed with the cosine of the angle between your heading and the wind direction to extract the component of your speed that is aligned with the wind direction. This process is repeated every second. Some averaging is then performed to make the output smoother and easier to interpret. The results are displayed on the LCD screen.


----------



## jarcher (Jul 29, 2008)

tommays said:


> The S10 calculates the heading from the downwind reference point to the upwind reference point. This heading is assumed to be the wind direction.


And therefor VMG is treated as velocity directly into or directly against the wind. It's merely coincidental that the windward mark happens to be up wind 

I suppose this is better than nothing, but wind does shift. I guess if you want to steer to VMG then its better than nothing.


----------



## SEMIJim (Jun 9, 2007)

jarcher said:


> Well VMG to mark vs VMG to the wind are referred to differently in different places. Here is one example:
> 
> Why VMG Matters - a knol by John Navas
> 
> Ockam and Nexus both use VMG to mean directly into or against the wind, and I have found that this is common when referring to racing.


Several months ago a sailor posted another solution, using a standard GPS: At the start, and as you round each mark, set a waypoint quite a way beyond the next mark (IIRC he suggest a couple thousand miles), on the same bearing as the bearing to the next mark. That way you don't encounter the problem, mentioned in the cited article, of your VMG decreasing as you approach the mark, because you'll never get even close to the far-off waypoint.

Exactly how you go about doing that, I'm not sure. A nice addition to GPS software would be a "VMG on course" (?) display, where the GPS would do this for you. That way you could still display bearing, distance, etc. to the actual mark, but the course VMG would be calculated based on the far-off pseudo-waypoint. Otherwise, I guess you'd need two GPS'.

I found the article I described above: VMG & GPS: VMG USE MADE EASY ("VMG FOR DUMMIES")

Jim


----------



## SEMIJim (Jun 9, 2007)

stardvd555 said:


> They'll usually give you a bearing and distance from the previous mark or starting line if its a drop mark course. Check your SI's.


That's not the problem with the GPS method. The problem is figuring out how set a waypoint _way_ off in the distance on that bearing. (I haven't tried it yet, so maybe it's not all that difficult.)

Jim


----------



## maxmunger (Dec 29, 2005)

The race course is always posted by RC. Either a series of marks or an Olympic course. Either a diagram or a list/map of set marks is provided in the SI's.
Put the waypoints in any little GPS and it will guide you to all of them. With critical boat info including current effect.


----------



## TSOJOURNER (Dec 16, 1999)

SailCruiser Pro polar data screen

We always get pre-defined coordinates of each mark. Navigator enters the coordinates into the navigation system. Knowing the wind direction and course, it's possible to calculate target speed, if correct polar data is also entered into the system.


----------



## jarcher (Jul 29, 2008)

Cool software, I'll check it out.


----------

