NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Voyaging the traditional way
From: George Huxtable
Date: 2004 Nov 4, 00:23 +0000
From: George Huxtable
Date: 2004 Nov 4, 00:23 +0000
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? ================== 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. ================================================================