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Subject: Re: log lines
From: Trevor J. Kenchington (Gadus@XXX.XXX)
Date: Tue Jun 10 2003 - 22:26:47 EDT
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@XXX.XXX Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555Science Serving the Fisheries http://home.istar.ca/~gadus
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