Speed measuring half - Raymarine ST60+

[marty9876]

Any suggestions on where to start troubleshooting appreciated - ever since launch this year by speed instrument has been measuring almost exactly 1/2 speed. Will say 0 knots up until actual boat speed of 3 knots and then it will measure 1/2 speed rest of the way - e.g 3.2 when the boat is going 6.4 per gps and my typical engine crushing speed.

Bottom was painted before launch by the yard, unsure if paint got sloped on the transducer or of the lift straps messed up the transducer. Airmar 20-399-01 model transducer with Raymarine St60+ display. I’ve not yet dived the boat, it’s in Lake Superior and the water if finally about as warm as it’s going to get. Before I freeze I figured I’d ask on the forums.

[Unity]

You should be able to remove that from the inside. Most ST60+ have a flapper that will seal up as soon as the speed is removed and you should have a plug (by raymarine) that you can then put in to stop the trickle. But even if it doesn’t have the flapper, or it doesn’t work, you have plenty of time. The column of water is impressive, but you can just put your have over it while you prepare to insert the plug. Worst case is have a wooden plug and a friend to hold it in place while you inspect the paddle wheel. Don’t hammer in the plug or you risk breaking the plastic column.

[Suijin]

I generally only put my transducer in when the boat is going to be moving.

As unity mentions you should have a blank plug for the transducer somewhere. If not you can buy a replacement part. It will be important to have in further and will allow you to pull the transducer and examine it and clean it at your leisure.

[jamhass]

There is a calibration setting that can be set.

[Rapanui]

Could be fouled given that it does not read at low speeds. Or one of the magnets on the wheel has dropped off

[marty9876]

Thanks for the info, popped it out and it’s missing a paddle/magnet

If thinking it’s a good idea to pull that transducer before hauling the boat in the future.

[sailcrazy]

We mistakenly left our ST60+ speed sensor in the boat when we hauled out 2 yrs ago...and the sling deformed the edges and broke a paddle off. Had the same problem as you, even after I made a new paddle and epoxied it in place. Ended up buying a new paddlewheel and installing it.....it's worked perfectly ever since. EZ fix.

[toddster8]

Hmm... rushing off now to pull my paddlewheel.


Wait. That didn't sound right...

[jeff356]

Pull mine if leaving the boat for more than a few days. Mine is unpainted and make sure it is clean and rotating freely. Even so lately I was always showing 1-3 knots slower than SOG on the chart plotter until I cleaned the bottom with a brush on a stick, removing some built up slime and growth. Needs clean water flow to give accurate readings. Now I can tell tidal effect and can use it once again

[Jimpitt]

My boat is also in Lake Superior. The advice you've been given about pulling the sensor while in the water is okay. The boat won't sink. I will state that every autumn at haul-out I remove the sensor while in the water because it is definitely in the way of the lift strap. I can also state that there is a calibration process that you should be able to find the in the Raymarine documentation. Sadly it is a process I'm just not interested in doing as I've found my GPS SOG to be pretty darn accurate. My question is: why does not the Raymarine C80 use SOG in the calculation for True Wind Speed?

[KeithB]

We have the same ST60 paddle wheel and only recently discovered that it is easy to remove and clean from inside the boat.
After years of unreliable through water speed it now works perfectly BUT it has changed itself to read in Kmh instead of knots. I have tried all the calibration techniques in the book but the damn thing won't show anything but Kmh.
Any ideas?

[Jimpitt]

Keith - Do you have a tri-data instrument? Or maybe a Raymarine multi-function display like a C80? From my experience I believe you can set speed through the water to "knots" in either location. Also there is a "multiplier factor" that you can apply when calibrating the speed through the water sensor (paddle wheel). The calibration requires motoring over a known distance (like a mile) at a set speed and noting the time, then repeating in the opposite direction. Tedious and difficult to come up with the "known distance". GPS helps. The calibration is managed using the tri-data. I have had difficulty getting the multiplier factor to hold static in the system when turning it off and back on.

[carstenb]

Originally Posted by KeithB

We have the same ST60 paddle wheel and only recently discovered that it is easy to remove and clean from inside the boat.
After years of unreliable through water speed it now works perfectly BUT it has changed itself to read in Kmh instead of knots. I have tried all the calibration techniques in the book but the damn thing won't show anything but Kmh.
Any ideas?

I believe the sequence is

depress and hold "disp" and "speed" at the same time for 3 sec. then use the "speed" button to go through the men. At some point the KMH will start flashing, now push the trip button a couple of times and it will flash through miles, kmh and knots

push "speed" and "disp" for 3 secs to exit

I might have the sequence a little screwed up (writing it from memory) but you raymarine documentation will tell you how or else you will need to google it