NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Should all electronic navigation devices on a yacht be set to True or Magnetic?
From: Lu Abel
Date: 2009 Nov 21, 21:46 -0800
--
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
From: Lu Abel
Date: 2009 Nov 21, 21:46 -0800
By that reasoning, you would trust the oscilloscope blip-matching
inherent in Loran-A with the automatic calculations of Loran-C or GPS?
I don't mean to insult you, but the way electronic compasses do their compensation is to measure magnetic direction as the boat circles through 720 degrees. Making just one reasonable assumption -- that the boat's angular velocity is constant -- a deviation table can be created. It's not a whole lot different from the way one creates a deviation table or a Napier diagram the old fashioned way.
Having said all that, I firmly believe that one should at least once do a manual deviation table. Why? Because the one thing that this method can't detect is whether the lubber line (whether on a traditional compass or its equivalent in an electronic compass) is aligned properly with the boat's keel. On my otherwise high-quality boat, it wasn't until I created a deviation table that I discovered that my lubber line was out of alignment by a couple of degrees! (with a steering-pedestal compass it's hard to see if the lubber line is aligned with the tip of the bow -- especially since there is this vital propulsion component called the "mast" in the way).
For those unaware, if one creates a plot with 0-360 on the horizontal axis and deviation on the vertical, deviation should form a sine wave symmetric around the X-axis. Vertical displacement means the lubber line isn't aligned with the keel.
Greg Rudzinski wrote:
I don't mean to insult you, but the way electronic compasses do their compensation is to measure magnetic direction as the boat circles through 720 degrees. Making just one reasonable assumption -- that the boat's angular velocity is constant -- a deviation table can be created. It's not a whole lot different from the way one creates a deviation table or a Napier diagram the old fashioned way.
Having said all that, I firmly believe that one should at least once do a manual deviation table. Why? Because the one thing that this method can't detect is whether the lubber line (whether on a traditional compass or its equivalent in an electronic compass) is aligned properly with the boat's keel. On my otherwise high-quality boat, it wasn't until I created a deviation table that I discovered that my lubber line was out of alignment by a couple of degrees! (with a steering-pedestal compass it's hard to see if the lubber line is aligned with the tip of the bow -- especially since there is this vital propulsion component called the "mast" in the way).
For those unaware, if one creates a plot with 0-360 on the horizontal axis and deviation on the vertical, deviation should form a sine wave symmetric around the X-axis. Vertical displacement means the lubber line isn't aligned with the keel.
Greg Rudzinski wrote:
The corrections aren't displayed or quantified in any way. I prefer a deviation table. On Nov 21, 8:21 pm, Lu Abel <lu...@abelhome.net> wrote:Greg Rudzinski wrote:New units today are suppose to automatically correct for deviation after circling a few times. A feature which I would find hard to trust.GregWhy?
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com