Compensation of Compass with GPS....

[D. Stump, Hanalei]

Want to find out how to compensate your compass using a GPS? Try this site for instructions:www.ritchienavigation.com/compensal.htm
Very clear instructions from a manufacture. Your GPS should be set on "Auto" heading with the local variation indicated.

I'm going to turn my compass this weekend and see how it works. Will let ya all know...I remain....

Dave Stump
Captain Commanding
s/v Hanalei CD-30

[John R.]

Want to find out how to compensate your compass using a GPS? Try this site for instructions:www.ritchienavigation.com/compensal.htm
Very clear instructions from a manufacture. Your GPS should be set on "Auto" heading with the local variation indicated.

I'm going to turn my compass this weekend and see how it works. Will let ya all know...I remain....

Dave Stump
Captain Commanding
s/v Hanalei CD-30

Dave the address you list is incorrect. I've posted the correct link below. Thanks for informing us of the page.

[John R.]

Want to find out how to compensate your compass using a GPS? Try this site for instructions:www.ritchienavigation.com/compensal.htm
Very clear instructions from a manufacture. Your GPS should be set on "Auto" heading with the local variation indicated.

I'm going to turn my compass this weekend and see how it works. Will let ya all know...I remain....

Dave Stump
Captain Commanding
s/v Hanalei CD-30

Dave the address you list is incorrect. I've posted the correct link below. Thanks for informing us of the page.

[Jon]

With all due respect, calibration by GPS is inherently tricky. A compass shows which way the boat is POINTING, while a GPS shows which way the boat is GOING. As an example, sailing magnetic north at 3 knots (per log) through the water will show a heading of 0 degrees M on the compass. However, If you have 4 knots of current on the nose, the GPS will assure you of your 180 degree course and one knot speed. Cross currents only compound the issues. The compass and the GPS are both great, but very different navigational tools.

Jon
s/v Sovereign
CD25 #625

[len]

dave

one of my compass magnets broke last year so i had to swing the compass this year after installing the new one - you can do it using gps, the key is to go from point A to B and see what direction GPS says A is when you get to B - you can't do it by seeing what course GPS says you are on - flat water and no current help, at least one mile is recommended - i found it was best to use a buoy as one of the points - you need a north-south course and another one at right angles - i did it alone and it came out fairly well, it would be easier with a second person aboard - for maximum accuracy you go back and forth correcting half the error each time - i am sure the website you mentioned has all the details - good luck

len



md.frel@nwh.org

[D. Stump, Hanalei]

I was simply providing a link to Ritchie, the compass manufacturer who provided their directions for compensating a compass. That's all I know. Oh, the link was wrong, see John R.s' link for the correct connection.

Dave Stump
Captain Commanding
s/v Hanalei CD-30

[Matt Cawthorne]

Jon,
The GPS system works perfectly, if you follow the directions on the web site. It says to use the "to" feature of the GPS. That means you type in the coordinates of a bouy which is reasonably far away and use the GPS to give you the magnetic course to the bouy. Point your boat to the bouy and no matter which direction the current is taking you the boat is pointed in the direction to the bouy and that is what you need to compare to the "to" function on the GPS. The compass does not tell you which way you are going, just which way you are pointed. Boats can be a great metaphor for life.

Matt



mcawthor@bellatlantic.net

[D. Stump, Hanalei]

Captain Cawthorne,

In fact, I grabbed my Garmin 48 to make sure I understood what they said. The mark you are heading for IS the visual reference for the helmsman. The GPS WILL tell you course to stear, and hence magnetic heading. 'nough said...I'm going to do it Sunday, if the storms blow through...Will let you all know what I see...

Dave Stump
Captain Commanding
s/v Hanalei

[Jon]

Matt,

I missed the "to" part. This would be "goto" on a Magellan GPS unit. As my Magellan 315 doesn't have nav aid locations, I imagined a direct comparison of compass and GPS motion readings. My error.

All the best,
Jon

[Bill Stebbins]

I did it yesterday and it worked fine. For the sake of greater accuracy go the buoy that you will be moving toward (more accurate than calculating it from the chart)and punch in its waypoint first and then construct a sight (as in gun) out of tape and and a couple of sticks of wood with part of it on the bow and the other close to your steering position but parallel to the compass lubberline and to the keel. Do it in as close to a flat calm as you can get. It took less than an hour allowing for checking twice. One of us steered with an eye on the sight and the other adjusted. Based on an article in Ensign - the magazine of the USPS for June 2000.



stebbins@umich.edu

[Neil Gordon]

For the sake of greater accuracy go the buoy that you will be moving toward (more accurate than calculating it from the chart)and punch in its waypoint first ...<<

For the best accuracy, use a land based or otherwise fixed object. Buoys are rarely in their exact charted position.


Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167



cdory28@aol.com

[Bill Stebbins]

For the sake of greater accuracy go the buoy that you will be moving toward (more accurate than calculating it from the chart)and punch in its waypoint first ...<<

For the best accuracy, use a land based or otherwise fixed object. Buoys are rarely in their exact charted position. That is why you go to the buoy to get its exact position and then punch in the waypoint



Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167

stebbins@umich.edu