Taking the ground with a paddle wheel

[homa]

Have just bought a lifting keel yacht fitted with a trailing log.

On previous boats I have always had through hull paddle wheel or propellor type sender unit.
I would like to istall a through hull sender unit.

My ideal is the very expensive induced resistance type (looks like an echo sounder transducer - no moving parts) all commercial ships now have them. Big advantage is flush hull, no moving parts and no cleaning required. However, they're very expensive. The cheapest and most common on yachts is the paddle wheel, OK but when the keel is fully retracted & the boat takes the ground the paddle wheel most likely gets damaged.

I believe some Paddle wheels can be retracted inside the hull fitting without total removal. Also some fittings can allow removal for cleaning without ingress of large amounts of water. Anyone know of the manufacturer/type. or have a an alternative recommendation to the problem.

If I stick with my trailing log it's only a question of time before I or my crew forget to recover the impellor & reverse over it.
Tx

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[StugeronSteve]

I have a B&G log, with through hull paddle wheel that self seals fairly efficiently. I withdraw the paddle wheel whenever leaving the boat to prevent fouling, and ship very little water in the process. I think Echopilot make a acoustic (doppler?) log transducer that isn't too expensive.

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[tillergirl]

My Raytheon (Ray Marine) log can be replaced by a blank and has a sealing flap that works quite well. When I had my last mooring, where she sat in the mud, the old NASA transducer survived ok. Generally you had to give her a bit of a go with the engine to clean off the mud. The occasional barnacle required it to be withdrawn but it wasn't quite as bad as you might imagine (that's soft mud though)

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[l'escargot]

I've got a NASA paddle wheel and sit on the mud for about half of every tide. I usually find that within the first mile the mud washes off and the log starts reading. Maybe once or twice a season I have to pull it to give it a clean. Done afloat with a blanking cap, I only reckon on shipping a couple of pints of water.
I wouldn't bother fitting a log at all now, a basic handheld GPS is cheaper and speed over the ground is a far better indicator, with "TTG" thrown in to see if the pub is still going to be open.

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[Birdseye]

i have a paddle wheel log in a boat that takes to the ground (mud) every 12 hours. no problems other than the need to give a blast to start the wheel when its a bit clogged.

but why bother? now that selective availability has gone, a gps will give you an excellent speed figure for no more electricity than a log. and the number it gives is, in fact, far more useful since it includes the effect of tides. i struggle to think of a single situation in which the water speed would be of more interest than the speed over the ground.

ask yourself - if gps had been invented first, would anyone bother to install a new fangled log that only gave you speed through the water?

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[homa]

Thanks for all your posts but I do want speed through the water. It is very important to me. I want to know how fast (or slow) I'm going through the water for sail trimming etc. For this reason alone SOG is absolutely no good unless I also know the WS (water speed).
By careful comparison with GS & WS (& leeway) one has a much better appreciation of what's going on. Tide tables & current chartlets are after all just a guide.

Taking the ground with a paddlewheel is OK in mud, but I also want the capability to take the ground in calm conditions on shingle & sand. I have 2 very young boys who like building sand castles ! it would be nice to beach the boat on this type of surface ocasionally without damaging the log impeller.

As my boat is a shallow draft , the keel fully retracts, and with no proper bilge I don't want much leakage when retracting the impeller.

On one boat I sailed the impeller could be retracted simply by twisting and retracting into the housing without being completely removed (from the hull), water tightness was maintained by a couple of "O" rings.

To remove the impeller completely one unscrewed the end cap and removed in the normal way, quickly replacing with a blanking cap. Some water always poored in, but that particular boat had a nice deep bilge so no trouble keeping everything else dry. Unfortunately I cannot remember the make of the transducer.

I'll have a look at these self sealing hull fittings, though I understand they still allow some water in.



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[StugeronSteve]

They do let some water in, but very little, especially if you pull the transducer out swiftly, and once you've popped the plug in it's sealed again.

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