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Date: Mon Sep 29 2003 - 11:50:33 EDT
> Date: Sun, 28 Sep 2003 15:15:55 -0000
> From: "christina" <>
> Subject: taffrail logs
>
> a chip log may be a good
> alternative, measuring as accurately as possible the time it takes to
> pass a chip of wood from bow to stern, then doing the math to figure
> out your boat speed. there´s a formula for that but i dont know it.
> does anyone have that formula?
We can figure it out. We want boat speed in knots (nautical mile /
hour), and we'll have boat length (probably in feet), and time for the
chip to float from bow to stern (probably in seconds).
( LWL (ft) x 3600 ( sec / hour) ) / ( time (sec) x 6080.27 ( ft / nm ) )
= LWL / (1.69 x time ( sec ) )
So if you have a boat 30 ft on waterline (assuming you drop the chip in
even with the stem touching the water and measure time in seconds to
when the chip passes the transom), your calculation would be 30 / ( 1.69
x time ) or 17.75 / time (sec). If it takes 6 seconds for the chip to
float from stem to stern, you'd be going about 3 knots.
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