# Speed Sensor Cleaning - While Afloat?



## Undadar (Mar 24, 2011)

Howdy! I have a DataMarine speed sensor that is of the paddle wheel type and mounted via a thru-hull. Mine needs cleaned.

In addition to diving on it and waiting til the next haul out, I have read that I can remove the sensor while afloat. I have no doubt that the water comes onboard FAST when the sensor is pulled (I envision a garden hose turned on full blast). Obviously, having the plug in hand and a spare person just in case something unexpected comes up are requirements. Question is; has anyone actually done this? Is the flow of water as significant as I have described? Any advice/suggestions (including wait til haul out)? 

Thanks!

JdFinley.com | Sailing, development, and life with JD
You can observe a lot just by watching.


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## Donna_F (Nov 7, 2005)

As long as you're quick, the amount of water that comes through before you put the plug in won't sink your boat. It is, however, alarming the first time.

No one I know even bothers any more. They use their GPS.


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## Faster (Sep 13, 2005)

Some transducer through hulls have a flapper that closes behind the sensor when it's pulled.. maybe you'll be lucky and have such a one.

However pulling the sensor is certainly doable but it can be alarming how fast the water wants to come in... but it's a pretty big hole and even though there's likely less than 1 psi it looks like quite the gusher. When I do it I have a plug handy that I insert instead of the sensor so that when we haul out there's no concern of a strap damaging the impeller. A second person to stem the flow would be good if you're just wanting to pop it out, clean it and reinsert it.

You'll end up with a couple of liters in the boat to mop up if you're quick.



DRFerron said:


> ....
> No one I know even bothers any more. They use their GPS.


I still rely on 'through the water' speed indication for sail trim.. and comparing it with the GPS keeps me informed about how much current is affecting our passage (around here it can be 2 knots or more at times)


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## tempest (Feb 12, 2007)

It helps to have a small brush.. ( a stiff bristle toothbrush works ) to clean it with ready when you pull it. If I'm doing a quick clean..the bilge pump just pumps the water out...for a good cleaning, I'll pop a plug in...don't force anything in tight..just enough to stem the flow....


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## svHyLyte (Nov 13, 2008)

It takes all of about two seconds to pull the impeller and replace it with the dumb plug. You can easily press the pin out of the paddle-wheel and remove that and pull the paddles and then clean the paddles and housing. I do this on our boat about once a month. I spray the paddle-wheel shaft with a little SailKote to ensure the wheel spins freely and then apply a little Neosporin to the paddle-wheel and the plug to slow down and growth. When the water's cold that's good for about 3 months. During the summer months--here in Florida-- it's good for 4-5 weeks.

FWIW we use a "KnotStick" to calibrate the Knot-meter. Speed through the water may not be useful to some, but we find it beneficial went evaluating apparent wind and of course, maintaining a DR.

FWIW...


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## TQA (Apr 4, 2009)

Have some one with a saucepan or wok ready to redirect the waterjet. 

Make sure the dumb plug is lubricated and although stress raising it is not difficult to do and less than a 1/2 gall of water should find its way into the bilges.


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## jackdale (Dec 1, 2008)

DRFerron said:


> No one I know even bothers any more. They use their GPS.


On a fully integrated system the knotmeter used in conjunction with the GPS and fluxgate compass will tell you your set and drift. I find that quite handy. Also just comparing the knotmeter and the SOG will help you with understanding current.

Racers use the knotmeter because there is less lag time. SOG is an average over time.


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## Ajax_MD (Nov 24, 2009)

I have the same Datamarine knot meter. The paddlewheel is fat compared to say, the Signet brand, and mine is way down low, near the centerline. The first time I swapped in the dummy plug, I almost shat myself the water came in so quickly.

You get over it. Just have the dummy plug handy, and a wooden bung handy, in case the water pressure ejects the dummy plug somewhere.


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## BarryL (Aug 21, 2003)

Hey,

If you don't have the plug, a regular wood plug will work too. You will get some water in the boat, probably around a quart.

Be prepared for A LOT of creepy crawly type critters on the sensor. I place the wheel in a plastic bag and then do a nice cleaning job with the sensor inside the bag so the critters don't go all over.

Barry


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## PaulinVictoria (Aug 23, 2009)

Heh, I did this a couple of months ago, it was almost as nervewracking as the first time she went back in the water after I fitted the new transducers. Anyway, my speed sensor came with a plug. I took a couple of old towels and arranged them around the through-hull, pulled the pin and then quickly yanked out the sensor and popped in the plug. Water column reached about 8 inches high, must have been a few pints of it in the second or two the hole was open. Pretty terrifying, but the little bit that the towels didn't catch just ended up in the bilge. You want to really picture what you're doing, fumbling with the plug can only end in tears


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## Undadar (Mar 24, 2011)

DRFerron said:


> No one I know even bothers any more. They use their GPS.


Understood. However; as noted by others, I would like the additional benefit that it provides. Since it is installed and working (just needs cleaned), seems like a no brainer.

JdFinley.com | Sailing, development, and life with JD
You can observe a lot just by watching.


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## Undadar (Mar 24, 2011)

BarryL said:


> Be prepared for A LOT of creepy crawly type critters on the sensor. I place the wheel in a plastic bag and then do a nice cleaning job with the sensor inside the bag so the critters don't go all over.


Good tip Barry, thanks! Creepy crawly type critters rate almost as high as water on my list of things that I do not like on my boat.

JdFinley.com | Sailing, development, and life with JD
You can observe a lot just by watching.


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## Undadar (Mar 24, 2011)

PaulinVictoria said:


> You want to really picture what you're doing, fumbling with the plug can only end in tears


Exactly my reason for having another person there when I do this. I can easily imagine a scenario that ends up with only my mast sticking out of the water... 

JdFinley.com | Sailing, development, and life with JD
You can observe a lot just by watching.


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## Pamlicotraveler (Aug 13, 2006)

Definitely you need "Boat Speed" via the wheel and "Speed Over Ground" from the GPS. In calm water make sure the paddle wheel speed is calibrated to the SOG so they are the same. Then any difference can be used to judge current. 

You need both!


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## svHyLyte (Nov 13, 2008)

Pamlicotraveler said:


> Definitely you need "Boat Speed" via the wheel and "Speed Over Ground" from the GPS. In calm water make sure the paddle wheel speed is calibrated to the SOG so they are the same. Then any difference can be used to judge current.
> 
> You need both!


Amen.

However, calibrating a paddle-wheel knotmeter/log can be a real pain in the neck. Over the years I have tried various methods but none were very satisfactory so I finally broke down and, for $49 USD, bought a "Knotstick" which is really nothing but a calibrated spring scale attached to a measured disk dragged behind the yacht on a leader. With this I can periodically run the boat up to 5 knots on the "Knotstick" and adjust our meter/log accordingly. The Knotstick can also be used on our sailing dinghy or inflatable so it has more than one application.

FWIW


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## dhays (Jul 9, 2010)

Pamlicotraveler said:


> Definitely you need "Boat Speed" via the wheel and "Speed Over Ground" from the GPS. In calm water make sure the paddle wheel speed is calibrated to the SOG so they are the same. Then any difference can be used to judge current.


I agree. I suppose there are many sailors who never have to worry much about current. Either they are on a river system with a fairly constant flow, or the Great Lakes, or regions with little tidal in the way of tide changes. Who cares all that much about a 1/2 knot current?

However, there are plenty of us who sail in areas where current is a big issue. SOG doesn't tell you how well your boat is trimmed when you have no idea of the amount of current at your particular location. Here is a shot of my plotter from a trip last week.









Here is a typical day through the Narrow, which I have to pass through a lot, anytime I want to go to the South Sound.


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## celenoglu (Dec 13, 2008)

You will have some water in the bilge but this will be manageble. Close the inlet with its own plug or use a wooden plug until you are done. clean the paddles throughly and paint them with antifouling. I normally keep a fingernail polish bottle from my wife filled with antifouling from the latest antifouling applied. I paint the paddle wheels when I apply antifouling to the boat and I rarely need to paint on the water.


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## erps (Aug 2, 2006)

If you don't mind getting a little wet and you have a second person, you can snorkle down to the the sensor and cover the hole from the outside with your hand while your partner pulls it out and installs the plug from the inside. It makes it a little less traumatic, as it really is alarming to see how much water comes through.


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## hellosailor (Apr 11, 2006)

Don't worry about being quick.

Quick usually means hasty and rushed, which means you'll botch the job.

Take your time, pull the impeller, put it down, insert the plug. If you take your time this normally will still take only 10-20 seconds and you'll take on an incredible amount of water, like a whole half gallon or gallon.

The first time you do this, have someone else on board with you. That way you know that if the worst happens, one of you can stick a finger in the dike while the other calls for pumps and rescue.

Really, not a problem.


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## jackdale (Dec 1, 2008)

The bilge pump(s) will easily take care of any water.

I often pull the sensors to clean or to show students how much water comes in through a hole that size.

Most newer boats have the flap mentioned earlier. You might get a half a cup of water into the bilge.

I would not have two people involved, they will just get in each other's way.

Remember to replace the sensor in the correct orientation; there is usually an arrow on the top.

Ray - I would not go into the water unless I was in Desolation Sound.


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## erps (Aug 2, 2006)

> Ray - I would not go into the water unless I was in Desolation Sound.


I hear you there, although I just grabbed my wet suit and gear off the workboat, as I will be changing zincs and cleaning the speed sensors on Nikko this weekend. Water temp should be somewhere between cold and real cold.


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## MarkSF (Feb 21, 2011)

Think of it as an opportunity to test the bilge pump!

My sensor must be lower down as I got a 4 ft high fountain of water... which landed quite nicely on the floor of the V berth. This is a plastic moulded floor which contains the water nicely until it can be bailed back into the bilge.

My knot log sensor was full of mud and live shrimp..the tiny ones.


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## dhays (Jul 9, 2010)

I've never done this myself and, to be honest, it makes me nervous to think about. I've got the plug tied to the spot where it would go if so some reason the sensor got knocked out, but I'd rather not swap them while in the water. I have a diver clean the bottom, clean the sensor, and check/replace the zincs every 3 months. 

However, I've noticed the last few times out on the boat that the sensor has taken a bit to start to register. Indication that it is getting a bit fouled. So, you never know I may have to man-up and pull it to clean. Not sure will get wetter, the boat's bilge or my own. ;-)

Dave


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## hellosailor (Apr 11, 2006)

Dave, some of us routinely pull the paddlewheel every time the boat is going to be secured. Once you get over it, it is no big deal, and keeping it routinely pulled is possibly easier than trying to get in there are clean out all the critters in fertile waters.

Wheel out, plug in...what's the line from the kiddie kung fu movie? "Wash off, wax on" ? 

Really, no big deal, and for MOST boats, no big soaking, either.

Well, unless you happen to pull the paddewheel and a giant narwhal spears the hole with his tusk before you can get the plug in. Now, that's scary when that happens. (WEG)


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## Boatsmith (May 3, 2009)

This is relly not a big deal. We usually will clean it on the way to the starting area on race days. It is a sponge job. A tooth brush is the tool. David


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## SVAuspicious (Oct 31, 2006)

As noted above it isn't a big deal. I pull the impeller every time I come back to the dock from sailing (although not each time we anchor out).

If you don't have the impeller in and calibrated--at least on my nav system--the true wind calculation is wrong and the cumulative miles log doesn't run.


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## carl762 (Jan 11, 2010)

Last time I cleaned my paddle wheel, the boat was up and out of the water. I noted the wheel's position and put a small piece of tape up on the toerail to mark its location. Now, I simply use the same brush I wash the boat with to whisk away the green slime and I'm good to go. 

One day, I'm going to plug that hole. The idea of quarts of water spewing up into my boat is scary.


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## jackdale (Dec 1, 2008)

If you have stuffing box on your boat, it leaks. Over a period of time you will get more water from it than from a periodic cleaning of your knotmeter paddles.


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## dinodino (Dec 9, 2002)

I do this all the time. Just have the plug in the other hand and ready to go. I'd say that you will get a shot of about 6 oz. of water if you are quick about it...a sponge will quickly soak it up.


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## Undadar (Mar 24, 2011)

dinodino said:


> ...if you are quick about it...


Therein lies some of my concern - I think I was a manatee in a former life..... 

JdFinley.com | Sailing, development, and life with JD
You can observe a lot just by watching.


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## FInella III (Nov 20, 2017)

Yes, I have done it on my Paceship 26. Not a big riisk. Only a gallon or so water comes in. Consider your thru hull is only about 1 foot below water. Water pressure is only about 1/2 PSI at that depth. (1 psi at 2 feet). Your average garden hose water supply is 50 PSI. It will gush up about 6 inches. But not blast you. SO, don't panic, just get the plug in.


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## SanderO (Jul 12, 2007)

The fouling problem I experience lately is as much the area AROUND the speedo. as the speedo itself. The flapper valve makes removing, and cleaning only a quart of water or less to deal with... Northport seems to be a very fertile environment for marine growth. I have the diver scrub once a month.. but even that is not enough.


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## HUGOSALT (Jun 15, 2004)

Welcome aboard FInella.
Some here will comment negatively about posting on years old thread but often times subject is still relative and informative for both new and old, such as this.
I must say that I have always been somewhat casual about removing/cleaning my knot meter and have used the stream of incoming water to help clean/rinse off paddle wheel.
(with blank nearby if things got out of hand)
But having said that, every time I do remove the paddle wheel, I also always picture a scene that could easily compete with any in the "Captain Ron" movie.


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## danvon (Dec 10, 2012)

First time I did this it took me an hour to make the dummy plug seal. Took it out, cleaned it, coated with vaseline, nothing worked. Couldn't get the speed sensor to seal again either. It was starting to get late in the evening and I was picturing spending the night on board running the pump. Then I figured out that the arrow on the cap was supposed to point BACKWARDS. Go figure. Maybe a narwhal tusk with butyl tape would have been easier.


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## outbound (Dec 3, 2012)

I pull it out if boat is stationary for more than a day and reinsert before leaving every time. It’s not a big deal. Also put a dab of Vaseline on a q tip and put it between paddle wheel and housing as any growth there prevents it from spinning. Growth elsewhere may impend accuracy but not function. Once or twice a year put transducer paint on all sections that are in the water. 
I don’t have a fully functional AP if paddle wheel isn’t spinning. We log both sog and speed through the water every 4h. Tells you what’s going on and allows you to think about your vmg.


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## knuterikt (Aug 7, 2006)

It's not that scary, through hull with flap.


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