# Is there a NON THRU HULL Knotmeter?!?!



## Amateur_Expert (Feb 20, 2012)

Good Morning,
Maybe it's me but I am having a heck of a time finding anything sailboat related without the exact search terms. For example "pulley" yileds NOTHING, you have to look for "block". Also "teak handles" yields absolutely nothing but "teak handrails" are just the ticket". Maybe it's just me.

My question is this: Is there a sailboat speedometer, speed meter or knotmeter (or knot meter) that can be installed WITHOUT cutting a hole in the boat?? Ie WITHOUT a paddlewheel? Also I don't know about thru hull or in-hull.. they sound the same to me.

I have an older Laguna Windrose 18'. It has an old Signet Knotmeter with a paddlewheel. I want to remove it because it hits the trailer when loading (the previous owner had a lever rigged up to pull it in a little but it does not work right. 

What I would like is a speed meter that has like a transducer or something mounted to the floor of the boat without a hole.

Any input greatly appreciated.

Thanks

Shawn T
Wichita KS


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## cb32863 (Oct 5, 2009)

I would think not, something has to be able to gauge your movement. If you have a handheld GPS, that will tell you your speed.


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## svHyLyte (Nov 13, 2008)

Amateur_Expert said:


> Good Morning,
> Maybe it's me but I am having a heck of a time finding anything sailboat related without the exact search terms. For example "pulley" yileds NOTHING, you have to look for "block". Also "teak handles" yields absolutely nothing but "teak handrails" are just the ticket". Maybe it's just me.
> 
> My question is this: Is there a sailboat speedometer, speed meter or knotmeter (or knot meter) that can be installed WITHOUT cutting a hole in the boat?? Ie WITHOUT a paddlewheel? Also I don't know about thru hull or in-hull.. they sound the same to me.
> ...


See JDC Electronic SPEEDWATCH Speedwatch Wireless Knotmeter with FREE UPS

For a less costly solution see Knotstick Sailboat Speedometers


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## SlowButSteady (Feb 17, 2010)

GPS will tell you your speed over the ground, which is really what you need for navigation. For boat performance (sail trim, et cetera) you need to tell your speed through the water. A paddlewheel knotmeter is, by far, the most common way of getting that info. There is at least one company that uses a thru-hull without a paddlewheel. I think it uses Doppler sonar, but it may use some other method. In any case it's VERY pricy, and you still have a thru-hull to worry about. However, there is something called a Knotstick which is just a little towed disk, and only costs about $50. They aren't nearly as complicated (or as "shippy-looking", or as pricey) as the old Taffrail logs, and appear to be fairly accurate, but may be somewhat of a bother to use.

D'oh! 
svHyLyte beat me to it, and I forgot about those SpeedWatch gizmos (actually, I thought they weren't on the market anymore). But they still have something mechanical under the boat to worry about. Have you thought about just relocating the thru-hull?


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## MarkSF (Feb 21, 2011)

Amateur_Expert said:


> Good Morning,
> Maybe it's me but I am having a heck of a time finding anything sailboat related without the exact search terms. For example "pulley" yileds NOTHING, you have to look for "block". Also "teak handles" yields absolutely nothing but "teak handrails" are just the ticket". Maybe it's just me.
> 
> My question is this: Is there a sailboat speedometer, speed meter or knotmeter (or knot meter) that can be installed WITHOUT cutting a hole in the boat?? Ie WITHOUT a paddlewheel? Also I don't know about thru hull or in-hull.. they sound the same to me.
> ...


Normally the knotmeter sensor is completely flush apart from the actual paddle blades which extend out. Are these really fouling the trailer or did someone install it wrongly so that the whole shaft is sticking out?

Also most knotmeter sensors unscrew to be replaced by a blank plug. In your case you'd have to do this before retrieval of the boat. After a while one tends to master the art of a quick swap without too much water coming in. The first time, you'll be amazed at how much water comes in! Better have that blank handy 

How about a pic?


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## Amateur_Expert (Feb 20, 2012)

Thanks so much for all the replies this morning guys!

I may have mis-spoke earlier... regarding the paddlewheel sticking out it APPEARS to be in the line of hitting the trailer. I am assuming (you know what they say about assume though) that along with the possible poor positioning and that the previous owner had a lever rigged to pull the paddlewheel in (hooked up to a rope runnig to the cockpit) that it will hit. I also simply don't like holes as well.

I have seen the knotstick as well as some VERY PRICEY units that may have the doppler.. have also seen that GPS can work although not totally accurate. I have also seen the wrist unit which is reasonable price-wise.

All I want is a installed mounted readout telling me how fast I'm going. You would think someone would come up with something simple like motor boats have (pitot tube) I mean it doesn't seem like rocket science. 

Anyhow, does anyone recommend a GPS that displays knots that I can purchase??

Thanks much!

Shawn T
Wichita KS


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## jrd22 (Nov 14, 2000)

I've seen transom mounted paddle wheels on power boats, try searching Defender of WM.


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## SlowButSteady (Feb 17, 2010)

Amateur_Expert said:


> ...
> Anyhow, does anyone recommend a GPS that displays knots that I can purchase??
> ...


Speed Puck

They're kinda pricey for a GPS with very limited functions.


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## CorvetteGuy (Jun 4, 2011)

Take a line and tie a knot in it every foot, drop it overboard and count how many knots go by in a given amout of time this is how many knots your doing:laugher:laugher


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## lajimo (Sep 5, 2011)

Most smart phones have cheap available apps that can provide speed info using their built in gps.


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## MedSailor (Mar 30, 2008)

A GPS is certainly the easiest way to measure speed over the ground, but it won't help you with speed over the water. In areas of current and tidal movement (like where I am) you really need both.

For speed over the water there is the old school:
Chip log - Wikipedia, the free encyclopedia
Good quality walker trailing logs can still be had and many a navigator has used them for accurate dead reckoning around the world (try Ebay):
Robert White

I agree though I'd rather have a better solution than the paddlewheel for speed over the water. Besides being another hole in the boat, barnicles and fishy things like to grow in mine rendering it useless. Guess I'm not going fast enough...

MedSailor


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## Liquorice (Nov 28, 2007)

Living in Wichita, Kansas, I doubt tide and current is a concern for you.
So a GPS based knot meter would be the way to go.
I use a speed puck. Pricey but works well and is bulletproof.
But consider something like iRegatta for your iPhone or iPad. I think it's free or close to free.
Or if it's something in your future, get a handheld GPS chart plotter. Most if not all have a page with large Didgital readouts of speed (over ground).
sam


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## overbored (Oct 8, 2010)

SlowButSteady said:


> There is at least one company that uses a thru-hull without a paddlewheel. I think it uses Doppler sonar, but it may use some other method. In any case it's VERY pricy, and you still have a thru-hull to worry about.


Airmar ultra sonic is the flush speed sensor used by may of the instrument companys. it is around $600 for the sensor with the thur hull. best speed sensor out. it has been dead on every time out and never needs calibration adjustments
CS4500 -Ultrasonic Speed Sensor - Airmar Marine Transducers


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## Faster (Sep 13, 2005)

overbored said:


> Airmar ultra sonic is the flush speed sensor used by may of the instrument companys. it is around $600 for the sensor with the thur hull. best speed sensor out. it has been dead on every time out and never needs calibration adjustments
> CS4500 -Ultrasonic Speed Sensor - Airmar Marine Transducers


There have been various attempts at Ultrasonic knotmeters over the years, the earliest utilizing a hull sensor and another at the base of the keel. This is one of many flow measuring techniques used in industry (flow is often determined by measuring the velocity and calculating the volume passed in a pipe...) So the technique is proven. This combined sensor from Airmar looks interesting.. some of Airmar's sensors have NMEA outputs of their own nowadays, making interfacing with other devices easier.

It is not the most reliable, repeatable velocity measurement technique so they don't seem to have caught on, OTOH overbored's experience would indicate otherwise.


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## PorFin (Sep 10, 2007)

I'm thinking that replacing your thruhull paddle wheel transducer with a stern mounted 'ducer would be the simplest solution if you want to go that way (as long as the new 'ducer is compatible with your existing display, that is.)

Like Mark mentioned, you should either have or be able to find a blanking plug to fit into the thruhull opening. Chances are very good that if the t/h isn't leaking now, it was installed competently and shouldn't be cause for undue worry.


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## hellosailor (Apr 11, 2006)

Powerboat style: Transom mount. Screws onto the transom and extends just below the bottom of it. No holes through the boat, the wires come up and over the transom, or through a hole above waterline.

The ultrasonics were gawdawful expensive, and had to be burrowed into the keel (and run up internally) as well as having other work done. Transom mount, or just make the hole for a paddlewheel. It isn't such a big deal, and you can almost always PULL THE WHOLE THING and insert a dummy plug, so it is protected when hauled on a trailer, doesn't get crud growing on it when moored, etc.

Really, no big deal compared to the costs, performance, and options.


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## asdf38 (Jul 7, 2010)

Just get a handheld marine gps. I have the garmin 76c. It's solid, waterproof and runs for hours on 2aa. If you don't have a gps you should have one anyway. 

You've been slightly misinformed. Gps is highly accurate if given a little time to work with. It's not perfect in a car which can rapidly accelerate but in a sailboat it's fine. And it can't get stuck with gunk and be stuck giving you bad (low) readings. 

Also, as others have said, any modern smartphone can be loaded with a gps based speedometer app, or better yet a full marine chart. See naviconics.


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## Faster (Sep 13, 2005)

asdf38 said:


> ......You've been slightly misinformed. Gps is highly accurate ......


GPS is great for speed over ground... not so great for through-the-water speed as a sail trim aid if current is a factor in your sailing area.

I 'need' both....


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## Screaming Seagull (Feb 11, 2012)

Get a smart phone with GPS. many awesome apps for sailing and general boating. Well worth the money, If you can afford a boat you can afforded a iPhone. I can't help you with the through-the-water speed.


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## donmikel (May 7, 2019)

Yes, you can get it on Amazon, it uses GPS and works great. I had to downsize my hole to fit the new meter. I used plexiglass and epoxy resin to fasten it. It added light inside my fuse cabinet which was a bonus!


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## Minnesail (Feb 19, 2013)

I realize this is a very old thread that got resurrected, but it's interesting.

Has anyone used one of the ultrasonic speed sensors? Paddlewheels seem like such a pain in the pita.

AIRMAR UDST800 Ultrasonic Smart™ Sensor


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## overbored (Oct 8, 2010)

I use the Airmar CS4500 speed and temp. it is about 4 years and works very well. dead on calibration never varies. we use a thru hull depth sensor but almost never look at it. no thin water here.


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## Minnesail (Feb 19, 2013)

capta said:


> The point is, the ultrasonic speed sensors and GPS are exactly the same. They tell you speed over the ground. A paddle wheel gives you speed in relation to the water you are in, two completely different things.
> If you have a good GPS plotter, it's pretty easy to see set or drift on the screen, otherwise, it is nice to have both speed sensors to help determine current.


Really? I thought they were using some ultrasonic magic to measure water turbulence or something to give you speed through water.


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## overbored (Oct 8, 2010)

capta said:


> The point is, the ultrasonic speed sensors and GPS are exactly the same. They tell you speed over the ground. A paddle wheel gives you speed in relation to the water you are in, two completely different things.
> If you have a good GPS plotter, it's pretty easy to see set or drift on the screen, otherwise, it is nice to have both speed sensors to help determine current.


not the same. the ultrasonic reads the particles in the water with two sensors a set distance apart to determine the speed thru the water, GPS works off a satellite and is slow to react.


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## capta (Jun 27, 2011)

Yeah. I guess there are newer ones.
Sorry, wrong again. My bad.


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