knotmeter paddlewheel

[Banooma]

After spending my first season convinced my knotmeter display or transducer had failed, I discovered this off-season that the paddlewheel was initially stuck. After a little playing with it, it's free to spin, but sometimes still sticks. Since my batteries are in storage, and I'm still in drydock, I won't know whether freeing the wheel solved my problem until after I've splashed. Is this generally a problem that can be resolved without replacing the through-hull? Any suggestions?

By the way, what might cause this problem? I noticed the location of the paddlewheel through-hull is precariously close to the marks left behind by the straps used to lift most boats out of the water. Coincidence?

 

[sailingdog]

Banooma—

You really should pull the paddlewheel and replace it with the dummy plug before hauling the boat. The paddle wheel protrudes slightly from the hull and could be damaged otherwise.

Marine growth on the paddlewheel or mud can stop the paddlewheel from turning. It doesn't take a whole lot to do so. Whenever you're leaving the boat sitting for more than a couple of days, it is probably a wise idea to pull the paddlewheel and replace it with the dummy plug. This is pretty easy to do, even with the boat in the water.

 

[Stu Jackson]

What vendor is the equipment? Datamarine has a great repair facility back east and I have purchased additional paddlewheels from them. DMI it's called. These are 22 year old things on our boat, still workin'. I also coat the new ones with bottom paint. I fear that after being away from my boat for over two months with my brokend leg that I'll have to pull it when I return to clean it out. I have about three backups, ready to go - now if I can only remember where I put them...

 

[Bill Roosa]

Paddle wheel PMCS

Preventative Maintenance Checks and Services for knotmeters:
Paint it with anti-fouling so the critters don't build up so fast and make sure once it dries that it turns freely.
Pull the unit when not in use.
Clean the unit as needed

This does two beneficial things:
keeps the unit working
keeps the unit in calibration

Pulling the unit while in the water is both easy and exciting. Have the dummy plug handy and practice the move BEFORE you actually pull the paddle wheel. The gusher of water that comes in through the 1+" hole in the bottom of the boat IS alarming the first time you do it but with a little practice it only introduces about a qt of water. The first time I tried this I had to futs with getting the dummy plug out of it's holder and it really got my heart pumping. About 4 gal of water entered the boat before I could get the dummy plug in the hole. I thought the boat was going to sink!

 

[Ray T]

In the early years I used to coat my paddle wheel with anti fouling paint. I later found I got better results by not painting. I would remove the paddle wheel after use and install the plug, It only takes a minute. If I accumulated some growth on the unit I would dip the paddle wheel in some Clorox killing the growth. I would reinstall the paddle wheel and the now dead growth would slough off as the boat moved.

 

[Steve L22188]

Boeshield will do the trick

I pull my paddle wheel in the Fall and install the plug. In the Spring, I clean the paddle wheel with one of those green 3M scrubby pads. Then, when the wheel if free and clear, I spray on liberal amount of Boeshield or other lubricant/protectant. Works great all Summer long.

 

[RECESS]

I was thinking of something today. I have a GPS unit that shows knots by the amount of distance you have traveled within the elapsed time. I also have a paddle wheel for my depth/fish finder. Which one do you think is more accurate? I have not installed the paddle wheel.

 

[sailaway78]

Measuring different things

Recess,
the two instruments are measuring two different things. The GPS is measuring speed over ground, or SOG. The paddle wheel measures you speed through the water. Confusing? Think about it this way. You are running a channel, with a two knot current in it. Your boat is making four knots through the water, either direction. You speed over the ground is two knots less going against the current, and two knot more going with the current.

 

[sinnettc]

I'm sure there' little/no current on our lake and I'm pretty much convinced the GPS is a lot more accurate than the horizon knot/depth/temp meter that came with Verboten. If I calibrate the knotmeter so it's pretty close at around 4 kts it reads high at faster speeds and low at slower speeds. Still, it gives a good estimate and it's really the depth sounder I'm interested in. Thinking i might make a sounding line and check the calibration on that too this year.

 

[Banooma]

hmmm

My equipment is Raymarine - not sure if it's ST50 or ST60 (I think it's original equipment and the boat is a '99). The notion of replacing it with a plug does not make sense to me because the paddlewheel is a permanent part of the outside ring of the through-hull, independent of the tranducer. I have removed the transducer, and the paddlewheel is not attached to it.

And yes, it was an exciting thing to do while in the water.

It is treated with antifouling paint, and will be again. There was no visible corrosion or dead sealife attached to it.

 

[sailingdog]

My equipment is Raymarine - not sure if it's ST50 or ST60 (I think it's original equipment and the boat is a '99). The notion of replacing it with a plug does not make sense to me because the paddlewheel is a permanent part of the outside ring of the through-hull, independent of the tranducer. I have removed the transducer, and the paddlewheel is not attached to it.

And yes, it was an exciting thing to do while in the water.

It is treated with antifouling paint, and will be again. There was no visible corrosion or dead sealife attached to it.

That may be part of the problem right there. Every transducer I've seen has the paddlewheel as part of the transducer and when the transducer is removed (pulled), the paddle wheel comes with it. BTW, Raymarine doesn't make the transducer, Airmar does, and I've never seen any airmar transducers that don't have the paddlewheel attached as an integral part of the transducer.

 

[Randy Rohrbeck]

The link is to a ST60 transducer which should look like what you're pulling.

https://valencemarine.3dcartstores....H-HULL-SPEEDTRANSDUCERFOR-ST60290_p_1263.html

I don't have Raymarine equipment on my boat so I'm assuming that's the correct picture. If it's not I'm sure others will point it out.

 

[Banooma]

Thanks Dog - that detail will be the first thing I check out when I get to the boat this weekend. I don't recall anything appearing broken, but I'm continuously learning about the P.O.'s care for my boat, and nothing surprises me anymore.

John

 

[larryw]

I pulled the wheel and put the plug in about six years ago, and haven't gone back since. The GPS gives me speed. Of course, the wind instru only reads one factor, and I don't have a rapid sample rate, but so what? I'm not racing.

 

[sailingdog]

GPS only gives you SOG, not STW. You're wind instruments can't give you True wind speed either. Sometimes having True wind speeds and Speed through water are important.

I pulled the wheel and put the plug in about six years ago, and haven't gone back since. The GPS gives me speed. Of course, the wind instru only reads one factor, and I don't have a rapid sample rate, but so what? I'm not racing.

 

[Scup]

In my harbor on Lake Michigan, zebra mussels are the main culprit for clogging the paddle. A quick dive over the side to remove the beasties does it for me.:dance:

 

[Witzend]

True wind speed should be calculated from a stationary point. It can't be accurately calculated using an offset from STW because STW is not an absolute, SOG is. I realize that the normal Raymarine setup factors in STW in determining True Wind using SeaTalk from the STxx Speed, but it is still not correct. It would be nice if the STxx Wind could calculate True from a NEMA or Sea talk GPS receiver. Other than this inaccurate "True Wind" plug, not sure why it is necessary to have a problematic paddle wheel indicating STW now that GPS has arived.

 

[Warren Milberg]

In addition to all the advice above about possible cause of knotmeter fouling, there is yet another possibility: a bent axle that the paddle wheel spins on. I had thought the Datamarine knotmeter on a previous boat was dead. I pulled the paddlewheel and drifted out the axle, only to find it slightlly bent and so the wheel could not spin freely. I cut a SS bolt to the right size and reinstalled the wheel. Worked fine.

 

[Banooma]

In addition to all the advice above about possible cause of knotmeter fouling, there is yet another possibility: a bent axle that the paddle wheel spins on. I had thought the Datamarine knotmeter on a previous boat was dead. I pulled the paddlewheel and drifted out the axle, only to find it slightlly bent and so the wheel could not spin freely. I cut a SS bolt to the right size and reinstalled the wheel. Worked fine.

A bent axle is something else I've considered, Warren. I'll revisit the details (and may have more questions for you) after I get to the boat this weekend.

 

[catsailor]

I'm with Larry. I have a plug in the hole.

I pulled the wheel and put the plug in about six years ago, and haven't gone back since. The GPS gives me speed. Of course, the wind instru only reads one factor, and I don't have a rapid sample rate, but so what? I'm not racing.

The wheel works fine. Too much trouble.

I go sailing to forget computers. True wind calculation? Feel it. Look at the waves, if you are running. Look to windward an watch the next puff coming. That suits me. Most days I don't even uncover the instruments.

How hard is it to do the calculation in your head, anyway? This isn't AC.