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Subject: Re: Distance off useing a hand held compass
From: David Weilacher (daveweilacher@XXX.XXX)
Date: Tue Mar 25 2003 - 12:55:10 EST
This is similar to estimating distance by using double the angle off the bow.
Sailing along the coast with a compass and speedlog only.
You sight an object that is 30 degrees relative to the bow. You are making 5 knots good. You wait until the same object is 60 degrees off the bow. It took 12 minutes from when it was at 30 until it reached 60. Since you traveled 1nm in 12 minutes, you can reasonably estimate that you are 1nm away from the object.
-------Original Message-------
From: "Royer, Doug" <doug.royer@XXX.XXX>
Sent: 03/25/03 03:06 PM
To: NAVIGATION-L@XXX.XXX
Subject: Distance off useing a hand held compass
>
> The following is a proceedure to find or estimate the distance off an
object
using a handheld compass.This is a quick dirty way of finding distance
when
other means are unavailiable.For you who are concerned with great accuracy
measurements just disreguard the following.A higher quality sighting
compass
may yield more accurate results.This is a good method for getting the
distance off of an object that is hard to reach due to terrain.
o
.
|
|
|
| d
A | B
a.-------------------------------.b
ref.
d = distance to be calculated
A = greater value of measured bearing
B = lesser value of measured bearing
a = 1st point of referance distance
b = 2nd point of referance distance
ref = measured referance distance
d = (tan(90-(A -B))) x ref.
It is imperative to lay the ref. line perpendicular to the object for more
accurate results.
1. Lay out referance line.I use a 10 meter cord.
2. Take a compass bearing from a to o.
3. Walk to the end of the ref. line and take the bearing b to o
4. Subtract the larger bearing from the smaller bearing.If B is larger
than
A switch positions in the equation.
5. Work the equation and the result will be the distance off the object.
Hopefully this diagram will be transmitted better than the one
yesterday.In
fact if this diagram goes through it was basically the same set-up as
yesterday's diagram.
>
Dave Weilacher
.US Coast Guard licensed captain
. #889968
.ASA instructor evaluator and celestial
. navigation instructor #990800
.IBM AS400 RPG contract programmer
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