NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: log lines
From: Trevor Kenchington
Date: 2003 Jun 10, 23:26 -0300
From: Trevor Kenchington
Date: 2003 Jun 10, 23:26 -0300
Dan Hogan wrote: > Walker type logs were intended for ocean passages, not for coastal cruising. > a dependable reading the log should trail at least 50 feet. That's a lot of > territory around a marina. With practice you can learn to read your wake to > within 0.5 Knots of speed. Otherwise I would use a Knotmeter. Conning your way around a marina isn't coastal cruising and taffrail logs very much were/are intended for the latter, as well as for ocean voyaging. Judging instantaneous speed is all very well (whether by visual observation, Doppler log or anything in between) but how does that help determine distance off from distance run? Look closely at the methods of pre-electronic chartwork, as presented in countless textbooks, and you will see (I do anyway) techniques built around an assumption that the navigator knows distances run, not speeds. Sure, given a speed log (who invented the neologism "knotmeter" anyway?), you can integrate over time to get distance run but if you don't have electronics to do the integration for you, you will have to work at it. Big ships from before 1860 tended to hold a steady speed through the inertia of hull mass and carried a sufficient crew to stream a chip log at frequent intervals, while the officers could concentrate on such navigational tasks as maintaining a reckoning. Most of us are in a quite different position today. Trevor Kenchington -- Trevor J. Kenchington PhD Gadus@iStar.ca Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555 Science Serving the Fisheries http://home.istar.ca/~gadus