When I put my new bulkhead mount compass on my boat last year, I did the man thing and screwed with the adjustments. At the time I thought I might like to have the thing read true north rather than magnetic. Now that I have a good hand-bearing compass, I need to undo my screwing with the thing. Anyone have any good resources (that I will read this time) for how to adjust a compass properly? Thanks. Dave
Adjusting a compass
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Here is a link
http://www.ritchienavigation.com/service/compensation.html Although it is a Ritchie link this method will should work with most compasses with compensating magnets. Make sure you use a screwdriver that has no magnetic influence.
http://www.ritchienavigation.com/service/compensation.html Although it is a Ritchie link this method will should work with most compasses with compensating magnets. Make sure you use a screwdriver that has no magnetic influence.
Malcolm's link
worked for me in adjusting my binnacle mounted compass. Yet I kept seeing significant differences between the compass and my GPS when sailing. I have a pedestal guard just forward of the binnacle/compass and had a foam holder there for an air horn, a handy location. It took a while to figure out that the metal cannister for the horn was close enough to the to compass to cause a significant error.... So, in addition to using a non-magnetic screw driver to adjust your compass, make sure all magnetic metals are also no where near your compass.
worked for me in adjusting my binnacle mounted compass. Yet I kept seeing significant differences between the compass and my GPS when sailing. I have a pedestal guard just forward of the binnacle/compass and had a foam holder there for an air horn, a handy location. It took a while to figure out that the metal cannister for the horn was close enough to the to compass to cause a significant error.... So, in addition to using a non-magnetic screw driver to adjust your compass, make sure all magnetic metals are also no where near your compass.
The adjusting screws are little rods with
short bar magnets on them cross wise. As you turn the rod you change the position of the little magnet and can even reverse the pole. If you turn it 360 degrees you are back where you started. Your chart will show the magnetic variation for your location. I set my compass at night with the boat pointed at Polaris and set the compass card to the variation. Then during the day I motor in an area with no current and swing the boat and watch both compass and GPS for 90 degree turns. Your compass should have come with a little bronze adjusting tool.
short bar magnets on them cross wise. As you turn the rod you change the position of the little magnet and can even reverse the pole. If you turn it 360 degrees you are back where you started. Your chart will show the magnetic variation for your location. I set my compass at night with the boat pointed at Polaris and set the compass card to the variation. Then during the day I motor in an area with no current and swing the boat and watch both compass and GPS for 90 degree turns. Your compass should have come with a little bronze adjusting tool.
A compass that reads TRUE NORTH??!!
Holy flux beams, Batman! Now if I steer toward Bermuda, I can land at Florida!!! Cool. That should throw off the evil empire..... Seriously, there is a simple proceedure that you can perform with the compass off the boat that will restore the compass to nominal magnetic readings. It is called "blocking the compass". The proceedure is this: Obtain or cut a wooden board that is about 12" on a side and perfectly square and a second, larger board that simply has a straight edge on it. Place the larger board securely on a non-metalic support in the middle of your lawn or driveway. Place the square board on top of the larger board so that one edge is even with the straight edge of the larger board. Place your compass on the square board such that the compass reads 0 degrees. Temporally secure the compass using double-sided sticky tape to the square board. Now turn the squard board with the compass attached 180 degrees so that the compass shuld read due south or 180 degrees. Since your adjustments are way off, you will not read 180 degrees, but something else. Adjust the correct screw so the compass now reads 1/2 of the error at 180 degrees. For example, if the compass read 170 degrees, you would adjust it to read 175 degrees. Now turn the compass 180 degrees back to north and check the reading. It should be about 5 degrees off using the above example. Turn the large board on it's support so that the compass now reads 0 degrees again. Turn the compass with the square board 180 degrees and check the reading again. Make another adjustment of 1/2 of the error as before. Repeat this process until the compass reads 0 degrees and 180 degrees when the square board is turned and aligned with the larger board. Now, repeat for 90 degrees and 270 degrees the same type of adjustments. The E-W adjustments will interact with the N-S adjustment to some extent. Repeat all adjustments until you can read 0, 180, 90, and 270 degrees with MINIMUM error by simply rotating the square board WITHOUT moving the large reference board on the bottom. This proceedure will get the compass adjusted to it's best ability WITHOUT taking into effect any deviation on your boat. IF you have a proper location on your boat and that location has no ferrous metal parts within a 3 foot distance of the compass, you should be completely adjusted. In real life, there will be some magnetic influence on your boat. If you then check your adjustment using the Ritchie proceedure sumitted by Malcolm, you should be able to eliminate any serious error. If you cannot eliminate all errors to be less than 2-3 degrees, either you have a low quality compass, or a "bad" location. FWIW, I check my compass each year by the above blocking proceedure and generally find that no adjustment is required.
Holy flux beams, Batman! Now if I steer toward Bermuda, I can land at Florida!!! Cool. That should throw off the evil empire..... Seriously, there is a simple proceedure that you can perform with the compass off the boat that will restore the compass to nominal magnetic readings. It is called "blocking the compass". The proceedure is this: Obtain or cut a wooden board that is about 12" on a side and perfectly square and a second, larger board that simply has a straight edge on it. Place the larger board securely on a non-metalic support in the middle of your lawn or driveway. Place the square board on top of the larger board so that one edge is even with the straight edge of the larger board. Place your compass on the square board such that the compass reads 0 degrees. Temporally secure the compass using double-sided sticky tape to the square board. Now turn the squard board with the compass attached 180 degrees so that the compass shuld read due south or 180 degrees. Since your adjustments are way off, you will not read 180 degrees, but something else. Adjust the correct screw so the compass now reads 1/2 of the error at 180 degrees. For example, if the compass read 170 degrees, you would adjust it to read 175 degrees. Now turn the compass 180 degrees back to north and check the reading. It should be about 5 degrees off using the above example. Turn the large board on it's support so that the compass now reads 0 degrees again. Turn the compass with the square board 180 degrees and check the reading again. Make another adjustment of 1/2 of the error as before. Repeat this process until the compass reads 0 degrees and 180 degrees when the square board is turned and aligned with the larger board. Now, repeat for 90 degrees and 270 degrees the same type of adjustments. The E-W adjustments will interact with the N-S adjustment to some extent. Repeat all adjustments until you can read 0, 180, 90, and 270 degrees with MINIMUM error by simply rotating the square board WITHOUT moving the large reference board on the bottom. This proceedure will get the compass adjusted to it's best ability WITHOUT taking into effect any deviation on your boat. IF you have a proper location on your boat and that location has no ferrous metal parts within a 3 foot distance of the compass, you should be completely adjusted. In real life, there will be some magnetic influence on your boat. If you then check your adjustment using the Ritchie proceedure sumitted by Malcolm, you should be able to eliminate any serious error. If you cannot eliminate all errors to be less than 2-3 degrees, either you have a low quality compass, or a "bad" location. FWIW, I check my compass each year by the above blocking proceedure and generally find that no adjustment is required.
power lines
Power lines can have a significant effect on compasses. If you are adjusting in your yard or driveway there might be powerlines nearby. I've noticed this with a simple handheld compass. I just check my compass with the gps. Motoring is important because sailing you usually have some sideslip. I confess that I use my compass as a general reference for the general direction that I'm traveling. I doubt that many people try to get precise readings off of their boat's compass for the purpose of traveling a long distance. Just a degree or two will throw you off miles. So I use visual landmarks or the GPS. Not to say that an accurate compass isn't an asset.
Power lines can have a significant effect on compasses. If you are adjusting in your yard or driveway there might be powerlines nearby. I've noticed this with a simple handheld compass. I just check my compass with the gps. Motoring is important because sailing you usually have some sideslip. I confess that I use my compass as a general reference for the general direction that I'm traveling. I doubt that many people try to get precise readings off of their boat's compass for the purpose of traveling a long distance. Just a degree or two will throw you off miles. So I use visual landmarks or the GPS. Not to say that an accurate compass isn't an asset.
GPS VS Compass
Just remember, unless the GPS has a built in compass, the Gps is giving you course over the ground/water and the compass is giving you the direction the boat is pointing. Can be a considerable difference when wind or current are present.. Fair winds DAve
Just remember, unless the GPS has a built in compass, the Gps is giving you course over the ground/water and the compass is giving you the direction the boat is pointing. Can be a considerable difference when wind or current are present.. Fair winds DAve
Tom, You must use your compass when steering
off shore but compare your course made good to your magnetic course steered and compensate your steering. If you are steering 020 and your GPS indicates that your course is 030 then you need to steer 010 to make good 020 and compensate for set and drift.
off shore but compare your course made good to your magnetic course steered and compensate your steering. If you are steering 020 and your GPS indicates that your course is 030 then you need to steer 010 to make good 020 and compensate for set and drift.
Gps withcompass
What I do with my handheld gps and compass is punch the goto button and turn the boat until I am going on the correct course. Then I look at the compass and note that heading. With this technique it doesn't matter if the compass is accurate only that it is consistent. It could be off 180 degrees and it wouldn't matter. My compass seems to be accurate except when I do something stupid like set my radio too close. My pedestal compass agrees well also with the compass in my binoculars. We routinely get a bearing from the binoculars and when we turn the boat to that heading we are pointing at the landmark. I confess that I haven't been out of sight of land in my boat. I've been about 10 miles out in the gulf and usually measure progress by looking for landmarks such as water towers on shore. My wife doesn't trust this technique and she drags out the gps every hour or two to check progress. At night I just watch the depth gauge and keep the lights on shore in sight. You can get away with this in the gulf because the depth changes fairly gradually. BTW during the recent cold weather my compass pulled a bubble. I brought it home and using the little fill hole added enough oderless mineral spirits to get rid of the bubble. I checked the Ritchie website to find out what to add.
What I do with my handheld gps and compass is punch the goto button and turn the boat until I am going on the correct course. Then I look at the compass and note that heading. With this technique it doesn't matter if the compass is accurate only that it is consistent. It could be off 180 degrees and it wouldn't matter. My compass seems to be accurate except when I do something stupid like set my radio too close. My pedestal compass agrees well also with the compass in my binoculars. We routinely get a bearing from the binoculars and when we turn the boat to that heading we are pointing at the landmark. I confess that I haven't been out of sight of land in my boat. I've been about 10 miles out in the gulf and usually measure progress by looking for landmarks such as water towers on shore. My wife doesn't trust this technique and she drags out the gps every hour or two to check progress. At night I just watch the depth gauge and keep the lights on shore in sight. You can get away with this in the gulf because the depth changes fairly gradually. BTW during the recent cold weather my compass pulled a bubble. I brought it home and using the little fill hole added enough oderless mineral spirits to get rid of the bubble. I checked the Ritchie website to find out what to add.
Just walk down
the fingers and look at everyone elses compass and that will tell you where yours should be set at. Providing of course they are all pointed in the same direction. I've checked mine for years doing it that way. Never failed me yet. Keep it up, Ctskip
the fingers and look at everyone elses compass and that will tell you where yours should be set at. Providing of course they are all pointed in the same direction. I've checked mine for years doing it that way. Never failed me yet. Keep it up, Ctskip
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