As a relatively new sailor it became apparent today, while installing audio equipment on my H23, the importance of keeping the compass as far from electromagnetic devices as possible, and after installing such the importance of checking and recallibrating the compass. While checking placement of new speakers I was amazed the effect they had on the compass, even six feet away. In the past I made a habit of using a portable cd/radio/tv in the cockpit, stowing it when not in use, but now see this could be a bad practice when keeping an offshore course. Conclusion: no unnecessary portable electromagnetic devices aboard cruising, especially on a small boat. Question: I need a lesson in compass calibration; any suggested articles or sites? Thanks
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Agree 100 percent!
Bought a little 2-1/2 inch "talk-back" speaker for my Standard Horizon LH-5 loud hailer which allows one to listen as well as talk back, sort of a combination microphone and mini-speaker. WOW! Like you experienced, even six feet away it still had an influence on the compass. My compass is a Wheems
Bought a little 2-1/2 inch "talk-back" speaker for my Standard Horizon LH-5 loud hailer which allows one to listen as well as talk back, sort of a combination microphone and mini-speaker. WOW! Like you experienced, even six feet away it still had an influence on the compass. My compass is a Wheems
Speakers
Mark, What kind of speakers did you use. I used low magnetic Ployplanar Platinum series and they have zero effect on the compass... And they sound excellent... Regards, Chris
Mark, What kind of speakers did you use. I used low magnetic Ployplanar Platinum series and they have zero effect on the compass... And they sound excellent... Regards, Chris
"Zero effect?"
Chris, these are standard weatherproof 6" coax speakers with pretty heavy magnets. They will be port and starboard, forward 8 feet to minimize and balance their magnetic effect. Still, this has brought to mind the effect of electromagnetic devices. Though I am sure there are methods to dampen magnetic interference (ferrous enclosures, for example) you can't eliminate their effect entirely. Without a gausmeter the effect is impossible to measure (and still there), so I'm thinking what should be done after installation of any such device is recallibration, if one wants to have any degree of reliability. (Having had bad experiences with electronic and electrical failure in accordance with the laws of Murphy I am leaning toward a "retro" approach to sailing). So, I post in hopes someone remembers this topic from somewhere, and can guide me in the right direction. Thanks for your input.
Chris, these are standard weatherproof 6" coax speakers with pretty heavy magnets. They will be port and starboard, forward 8 feet to minimize and balance their magnetic effect. Still, this has brought to mind the effect of electromagnetic devices. Though I am sure there are methods to dampen magnetic interference (ferrous enclosures, for example) you can't eliminate their effect entirely. Without a gausmeter the effect is impossible to measure (and still there), so I'm thinking what should be done after installation of any such device is recallibration, if one wants to have any degree of reliability. (Having had bad experiences with electronic and electrical failure in accordance with the laws of Murphy I am leaning toward a "retro" approach to sailing). So, I post in hopes someone remembers this topic from somewhere, and can guide me in the right direction. Thanks for your input.
Hey Mark
My speakers are mounted all the way forward in the main cabin so there is very little interference. My compass and GPS read about the same, but the fluxgate compass in the tillerpilot is off by about 20 degrees. Go figure. This won't be a problem much longer, as I'm about to wire the GPS to the tillerpilot via the NMEA socket. I'm also going to tackle the last of the blister repairs this weekend, so let me know if you want to come by and see how it's done. Peter H23 "Raven"
My speakers are mounted all the way forward in the main cabin so there is very little interference. My compass and GPS read about the same, but the fluxgate compass in the tillerpilot is off by about 20 degrees. Go figure. This won't be a problem much longer, as I'm about to wire the GPS to the tillerpilot via the NMEA socket. I'm also going to tackle the last of the blister repairs this weekend, so let me know if you want to come by and see how it's done. Peter H23 "Raven"
Deviation table
Depending on the location of the offending magnetic device, you may be able to adjust out some of its’ effect. However, you must remember that the induced error (deviation) changes with the heading of your boat. Imagine a single big magnet located about 3 feet directly in front of your compass. If you are headed due east, the compass will be pulled eastward of true north. When you change direction and are headed due west the compass will be pulled west of true north. Every heading will show some variation from these two extremes depending on other factors unique to each boat. In the end, if you can’t get satisfactory results by adjustments you will need to build a new deviation table to replace the one you are currently using. There have been many articles in the magazines and the United States Sail and Power Squadrons or the Coast Guard Auxiliary have classes and publications covering deviation table construction. Good Luck!
Depending on the location of the offending magnetic device, you may be able to adjust out some of its’ effect. However, you must remember that the induced error (deviation) changes with the heading of your boat. Imagine a single big magnet located about 3 feet directly in front of your compass. If you are headed due east, the compass will be pulled eastward of true north. When you change direction and are headed due west the compass will be pulled west of true north. Every heading will show some variation from these two extremes depending on other factors unique to each boat. In the end, if you can’t get satisfactory results by adjustments you will need to build a new deviation table to replace the one you are currently using. There have been many articles in the magazines and the United States Sail and Power Squadrons or the Coast Guard Auxiliary have classes and publications covering deviation table construction. Good Luck!
Other reasons
You may find, as in aircraft, that the deviation may also depend on if the engine is running, and even the rpm its running at. If the alternator is near and it has a larger draw due to charging of batteries. A generator can cause the same effect, so if you will be running the engine in fog, you may want to have a separate card for both operating conditions.
You may find, as in aircraft, that the deviation may also depend on if the engine is running, and even the rpm its running at. If the alternator is near and it has a larger draw due to charging of batteries. A generator can cause the same effect, so if you will be running the engine in fog, you may want to have a separate card for both operating conditions.
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