Speed log

[Scubafill]

I have an Airmar Bronze Thru-Hull Triducer Multisensor attached to a Raytheon ST60 Tridata Instrument on my Hunter 26 Sailboat. The boat is about 10 years old.

The speed reading has been unreliable for the last few weeks and finally would only read 00.00. The depth reading is correct.

I have fitted a service kit comprising of a new paddle wheel, bearings and shaft. I only get a reasonable reading while going astern, while going forward the instrument reads 0 for speed or occasionaly goes up to .70 knots when I know the boat is travelling at between 4 & 5 Knots.

I would apreciate any advice or suggestions anybody may have to resolve this problem.



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[Talbot]

have you tried turning the transducer through 180 degrees, or even checked the alignment of the transducer (should be pointing at the bow, rather than parrallel to the keel)

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[Scubafill]

Yes I have ensured that the arrow on top of the transducer is pointing towards the bow and that the paddle wheel is the correct way around to ensure the blades are in the most effective direction.

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[StugeronSteve]

Have you checked that you have not got some weed fronds trailing from the hull, which foul the log as soon as the boat is in motion, yet leave the paddle wheel free when you inspect it? I withdrew the paddle wheel then pulled a warp under the boat, cheese saw fashion, and worked it backwards and forwards over the affected area. Hope this makes sense, it worked for me.

<hr width=100% size=1>Think I'll draw some little rabbits on my head, from a distance they might be mistaken for hairs.

 

[Talbot]

Have you tried rotating the paddlewheel by hand (i.e. before putting it through the hull) This will prove if the problem is with the paddlewheel or with the rest of the system - if it reads a decent speed in both directions when it is out of the water, then it is possible that something is interfering with the paddlewheel when it is installed (weed barnacle etc) If it is not reading, in either direction, then possibly the connections are wrong, or the magnet has fallen out of the paddlewheel. If it doesnt work in one direction only then ask the manufacturer for further advice.

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[halcyon]

The paddle wheel is not directional, it only counts pulses as the magnet passes. If it reads in reverse, and not forward, it must be a blockage of some sort stoping forward rotation.

Brian

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[RBJ]

My Raymarine Tridata log started reading erratically a couple of weeks ago. Speed shown was zero or way too slow.

I always withdraw the paddlewheel before leaving the boat and replace it with the blank supplied. As the paddlewheel (2 years old) was in perfect condition I assumed a fault elsewhwere in the system.

However, when my boat was taken out of the water this morning and the problem was obvious.

I had carefully avoided antifouling the transducer and paddlewheel housing. Both resembled an underwater jungle. Copious amounts of weed were obstructing water flow over the paddlewheel. My prop shaft and propellor similarly affected. Elsewhere underwater the antifouling had done its job.

Roger

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[Scubafill]

Thanks eveybody for your help.
As a diver I propose to get underneath the boat this weekend to see if marine growth is the problem.
In addition I will be at Southampton boat show tomorrow and will have a chat with the suppliers.
Thanks again. What a usefull forum
Phil

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