Greetings, I just bought a 1985 Hunter 25.5. The previous owner installed a stereo system with bulkhead mounted speakers. Unfortunately one speaker is about 6 inches below the bulkhead mounted compass. It is a fluid damped card type compass. Unfortunately I did not note during the sea trial that the compass always pointed north! I am pretty sure that the speaker is putting off enough of a magnetic field to keep the compass pointing north. I brought a hand compass on board and observed the same behavior as the mounted compass. So my question is how do I fix the problem? Can I use a correction magnet placed in the right location to offset the field produced by the speaker? Can I buy a special type of speaker that will not interfere with the compass? An obvious solution would be to move either the compass or the speaker but doing either would leave large holes in the bulkhead and in addition there is no other place to move them to. Thanks so much in advance for all your help.
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Previous owner must not have used compass!
Yes, if you don't want to move your speakers, Poly Planar makes waterproof magnetically shielded speakers, but 6" from a compass still seems kinda close... I would buy a new set, remove the old speaker, hold the new speaker in the same location and see if there still is a major problem. (Do not destroy the packaging so you can return them if they still affect the compass). A "normal" amount of deviation can be compensated for, but a compass that always reads North is a different matter!
Yes, if you don't want to move your speakers, Poly Planar makes waterproof magnetically shielded speakers, but 6" from a compass still seems kinda close... I would buy a new set, remove the old speaker, hold the new speaker in the same location and see if there still is a major problem. (Do not destroy the packaging so you can return them if they still affect the compass). A "normal" amount of deviation can be compensated for, but a compass that always reads North is a different matter!
shield
The best solution is the one you've already rejected, move one of them. Here are two ideas that just might work. Try placing a steel shield between the speaker and the compass, it wouldn't have to be heavy steel just a magnetic shield. Try to find a speaker that does not have a permanent magnet in it. Good Luck Phil Teter Force 1
The best solution is the one you've already rejected, move one of them. Here are two ideas that just might work. Try placing a steel shield between the speaker and the compass, it wouldn't have to be heavy steel just a magnetic shield. Try to find a speaker that does not have a permanent magnet in it. Good Luck Phil Teter Force 1
shield
Thanks to George and Phil for the input. Phil when you say put a shield between the compass and the speaker, what would be needed as a magnetic shield? Would sheet metal work?
Thanks to George and Phil for the input. Phil when you say put a shield between the compass and the speaker, what would be needed as a magnetic shield? Would sheet metal work?
Shielding Metals
The material you need is netic, conetic, or u-metal -- I haven't had very good luck shielding with cold rolled steel unless you completely surround the speaker with it. Not too practical. The 'safe' speakers made for computer and TV use also limit the amount of magnetic flux leakage by design as well as shielding. What's the possibility of using a flux gate sensor remote mounted and an indicator in the bulkhead cutout? Ken S/V Wouff Hong
The material you need is netic, conetic, or u-metal -- I haven't had very good luck shielding with cold rolled steel unless you completely surround the speaker with it. Not too practical. The 'safe' speakers made for computer and TV use also limit the amount of magnetic flux leakage by design as well as shielding. What's the possibility of using a flux gate sensor remote mounted and an indicator in the bulkhead cutout? Ken S/V Wouff Hong
flux gate compass
Thanks Ken. That is a great suggestion. I hadn't even thought of using a remotely mount fluxgate compass. I guess the only problem is finding a display that will fit in the same hole, but that should be to hard. The only real hitch is that it will probably cost me alot for the compass and display. Do you have any suggestions as to which one I should get?
Thanks Ken. That is a great suggestion. I hadn't even thought of using a remotely mount fluxgate compass. I guess the only problem is finding a display that will fit in the same hole, but that should be to hard. The only real hitch is that it will probably cost me alot for the compass and display. Do you have any suggestions as to which one I should get?
This is getting expensive...
Isn't trying magnetically-shielded speakers first a lot cheaper than a $200.00 electronic compass which will swim inside your 5+" speaker hole anyway? (Unless of course you opt for Sailcomp's $1,145.00 Maxi Display...)
Isn't trying magnetically-shielded speakers first a lot cheaper than a $200.00 electronic compass which will swim inside your 5+" speaker hole anyway? (Unless of course you opt for Sailcomp's $1,145.00 Maxi Display...)
High Cost of Flux
Nope. No suggestions but you should be able to mount the display on a piece of Teak and maybe throw in a clock too. The automotive ones are cheap enough but only have 8 points..... not degrees. The racing people are always 'upgrading' so maybe there's a market out there for used ones. It's a matter of being there at the right time, I'm sure. My compass is in the Autohelm ST1000+ but it's pretty small. I use GPS a lot for speed and navigation but a lot of people don't understand that a GPS is NOT a compass. The Nav display looks like a compass card but it really has no idea which way you're pointing. Keep us posted. Ken S/V Wouff Hong
Nope. No suggestions but you should be able to mount the display on a piece of Teak and maybe throw in a clock too. The automotive ones are cheap enough but only have 8 points..... not degrees. The racing people are always 'upgrading' so maybe there's a market out there for used ones. It's a matter of being there at the right time, I'm sure. My compass is in the Autohelm ST1000+ but it's pretty small. I use GPS a lot for speed and navigation but a lot of people don't understand that a GPS is NOT a compass. The Nav display looks like a compass card but it really has no idea which way you're pointing. Keep us posted. Ken S/V Wouff Hong
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