Paddlewheel position

[alan43]

Where is the best location for a log paddlewheel transducer?
And what problems or inaccuracies might arise if located elsewhere?

The boat is a fairly slim 25foot, with a long and deep keel and a keel-hung rudder with a cut-out for the prop. The old spinner (not a paddlewheel & now defunct anyway) is tucked up under the stern just forward of the trailing edge of the keel and the prop.
I've been led to believe that the log paddlewheel should be ideally located forward of the keel, as close to the centerline as possible, and with its axis as close to the horizontal as possible. Internal access to that area is not easy, and it would mean a long cable run.
Would it matter very much if the paddlewheel was located alongside or behind the keel, or off the boat centreline, or at an angle to the normal, or any combination of those three?
Should I expect a significant difference in readings from opposing tacks?

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[tillergirl]

I think you have described the ideal position but like you I could not put it on the centre line. Putting it aft of the keel would I think give it a nasty bit of turbulence and thus to be avoided. I have might slightly to starboard of the ideal position, about a foot and a bit clear of the centre line and any turbulence and it seems to be accurate. Making the block to get the thing upright was a challenge but the paddlewheel makers sell a plastic type block that can be cut in two at the right angle to make both an internal and external fairing piece. There was very little tolerance to get it right!

As to accuracy on each tack, I've always thought TG sails better on starboard tack than port - perhaps it's the log.

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[Trevor_swfyc]

I think you have worked out the best place, but as you point out the best place is not the easiest in terms of access and run length. I was going to fit mine in the engine bay as this looked the best place easy to fit and get at. I went round a boat yard and inspected where they were being fitted on new boats, most were in front of the keel/s so thats were I put mine. The log is about 1ft 6" in front of the keel to port and the depth transducer to starboard. The 1ft 6" allows plenty of room for a lift out strop. I drilled a pilot hole from the inside first, where it could be got at and it would not be accidently knocked. Don't know if I can mention it here but last year Sailing Today did a detailed instructional item on the Nasa Clipper log.

All the best.
Trevor

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[anabel]

Fit paddlewheel either side of keel, about 18" from keel itself. Not more or it will be too near surface & cause inaccuracies due to turbulance. Too far forward will also give inaccurate readings in rough conditions. There is no need for it to be vertical. Keep it in line with the curvature if the hull. As for the axis being correct. This is something you do when you fit paddlewheel into its housing. There is usually an arrow or pointer which you twist to have it dead ahead and so line up the axes of the paddlewheel. There is usually quite a lenght of cable supplied with the unit which should be more than adequate for a 25 ft boat. The main thing is to fit it in an area where there is minimum turbulance in all sea conditions.
Regards.
E.H.

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[William_H]

If you put the transducer in an area which will get close to the surface when leaning hard on one tack the log will fluctuate and drop in reading. The most important aspect is to put it in a place where you can remove it for cleaning. Sure here in oz the water is warmer but when I had a log I kept the paddle removed from the water until I actually went sailing and removed it after a sail. Otherwise it just fouled up with weed and crustaceans. Last winter I remioved it completely a GPS is the same price does a lot more and never fails. Mind we don't have much tide so speed over ground equals boat speed near as dammit. My advice don't fit it at all.

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