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Bill asked

>Regarding taffrail logs:
>
>While I have a used brass T.W, Cherub on my fireplace mantel, I have not
>used it nor do I have the counter (perhaps the wrong term?).  I have read
>that they tend to lose accuracy in following seas. (My guess is they run too
>slowly.)
>
>Could Robert, David, et al comment on their experiences of the accuracy in
>different types of seas at different points of sail?

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Response from George-

I've used a Walker taffrail log for many years. I don't make ocean
passages, but with that log astern I have been through some roughish water
(by my standards) in my time, in the "chops of the channel" and off the top
left-hand corner of France. But nothing like as ocean storm, glad to say.

It normally stays trailing from the taffrail unless I feel the need to
trail a mackerel line, as the two are incompatible. I've used it when my
nav was by DR and radio DF bearings, and also later, in conjunction with
GPS.

It's difficult, however, to make a good estimate of the accuracy of the log
in such (very) tidal waters as those I inhabit. However, it's only under
idle conditions that I have had cause to suspect if of inaccuracy, when it
tends to droop rather than trail. If I were in continuously heavy breakers
then I would start to distrust it, but would then have other troubles on my
mind.

The rotator never seems to jump out of the water, under the worst
conditions I have been out in. Parhaps a helpful factor is that my little
boat (on rather Folkboat lines) is very close to the water, with only a
couple of feet of freeboard, where the log is attached at the
stern-decking.

I think the most testing conditions for a trailing log are in a power
vessel that's pitching into a head sea. I made a passage in a small steam
coaster, rather lightly laden, back around 1950, and approaching Cape
Cornwall the pitching was severe enough to give the engine-room gang a lot
of work in winding the throttle-valve to control the racing when the screw
came right out. Standing at the taffrail was like being in a lift as it
went up and down, and the cord of the Walker log was making some very
strange angles with the horizontal. But it was a very long cord, and I have
little doubt that the rotator itself was trailing at a comfortable angle.
Somebody came aft from the bridge to read it, now and again.

As long as a vessel is being regularly passed by waves from astern, then I
suggest that the effect of those waves on the log averages out. That is,
being slowed when immersed in water moving the same way as the boat (and
the wave) when the rotator is at the top of the wave, then speeding up when
in the water moving the opposite way on the bottom of the wave. Swings and
roundabouts. But things may be very different for those fast multihulls
that are able to "surf" along the face of a wave for long periods.

This reply has been rather  anecdotal, I'm afraid, and I think Bill is
seeking something more numerical.

Finally, a word of advice to users of Walker logs. Look over the stern
before engaging reverse gear. Failure to do so cost me a rotator.

George.


================================================================
contact George Huxtable by email at george@huxtable.u-net.com, by phone at
01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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