NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Removing Deviation from the Ship's Magnetic Compass
From: Hewitt Schlereth
Date: 2013 Aug 6, 12:06 -0700
Sent from my iPad
From: Hewitt Schlereth
Date: 2013 Aug 6, 12:06 -0700
On sailboats I used the shadow cast by the gnomon on the compass and HO 260. The day before an appointment I would make a short table - incorporating local variation and local time - that gave the compass point where the gnomon's shadow should fall.
When I got my first computer (a TRS-80) I wrote a program that printed the table.
For powerboats with an inside compass, I used a gimbaled dummy compass and set the card point to the shadow.
Hewitt
Sent from my iPad
I used to use an astrocompass to measure the deviation on sailboats and to adjust the compasses. I temporally mounted the astrocompass on the cabin top by first mounting it on a board that I could slide up against the edge of the the hatch cover track to get its lubber line aligned with with the boat's keel, this usually came very close, and then a check by measuring the offset from the keel line. A little computation to set it up and then changing the LHA one degree every four minutes made it easy to determine the true heading. Apply variation and, voila. Done in smooth water in the harbor took less than half an hour.
gl
From: Hewitt Schlereth <hhew36{at}gmail.com>
To: garylapook{at}pacbell.net
Sent: Tuesday, August 6, 2013 7:30 AM
Subject: [NavList] Re: Removing Deviation from the Ship's Magnetic Compass
Yeah, Greg, good old Sol, our star. On days when it was overcast and a customer just had to have it done - start of vacation cruise or offshore passage - there were courses between a couple of buoys and a breakwater light that ran close enough NSEW for practical purposes.Hewitt
Sent from my iPadHewitt,The Sun was my preferred azimuth reference for checking the gyro. When at anchor or moored then a distant point of land got the job done.Greg Rudzinski
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