An attractive nuisance.

[caguy]

Here's a query for the egg heads of the group. Sorry I meant technically adept.
I am hoping to install speakers where the old instruments used to be. The wind gauge as well as all of the other gauges have gone kapoot. The compass is the only left that is working and is amazingly sensitive.
I picked up some 5" speakers to fill the holes. One will be above the GPS and the other will be above the compass. When I put the one in near the compass the compass changed readings by about 15*. The boat in my drive way is facing west an I have a feeling that I may even have a greater effect when facing north. Either way it is not good.
I was reading some articles about a product called Magnashield and was wondering if anyone has tried it here. I tried putting a coffee can over the magnet but it only made a slight difference.
I would really like to have the speaker mounted there but if worse comes to worse I could install a speaker grill only just for looks.
Any ideas are always appreciated.

http://www.lessemf.com/mag-shld.html#274

 

[Rich Stidger]

As I recall, speakers must be kept at least five feet away from the compass. Even at five feet, you should swing your compass and construct a deviation chart to understand the compass error on your sailboat.

 

[Rick Sylvester]

Don't do it

It's not just about the compass.

If the speakers were mounted relatively high in the cockpit (like in those existing holes) the sound from them will travel. Far. Very far. This may not matter when you're bombing along in the middle of the Atlantic ocean, however, I can assure you that you'll annoy everyone nearby in marinas and anchorages if you even want to listen to quiet tunes.

If the speakers were mounted down low (like in your lazarettes) the sound is attentuated greatly even a few feet outside the cockpit.

Also, you don't really want to look at the backs of those speakers when you're sitting in the cabin do you?

Fill the holes. It's not hard.

 

[Joe]

I agree with Rick... filling the holes and relocating the speakers to a lower cockpit position will solve many current and future problems.

 

[njsail]

When i needed to fill three five inch holes for my old Datamarine instruments I used a teak board with a few stainless bolts and some life calk. You can glass over it and spend hours trying to match the glass color or just put some teak over it and have the rest of your weekend to do other tasks. easy to maintain too. On our boat we have 2 small external speaker cubes mounted under the windshield/dodger. at anchor when we are on the back deck the relatively high placement allows for us to hear the music. We also have a full enclosure that help direct and keep sound aboard. Good luck.

 

[Don12364]

No Way

From the photo, and in your chosen position, the magnetic field from the speaker magnet will swamp that of the earth. By using the compensator magnets in the compass, or even by installing external ones, you will be very lucky to get the deviation down to acceptable limits for a steering compass.

All electrical devices have a "Compass Safe Distance" which is generally taken as the necessary distance between device and compass at which the compass does not deviate by more than one degree. For loudspeakers this can be as much as 2 metres.

Putting a mu metal screen round the speaker will, in itself, attract the compass magnet regardless of whether it is able to contain the speaker's magnetic field.

If you are dead set on this location you could consider installing a remote flux gate compass elsewhere in the boat with the repeater instrument in the existing location.
There are speakers made with 'closed' fields but even these will still leak some magnetic field and will probably have a steel chassis as well.

You asked for a technical opinion which you could understand: Well, it could be likened to farting against thunder.
Sorry but you will need to think again.

 

[catsailor]

Big magnets and a compass--bad. Also, check the compass with the speakers on; there may be a difference.

However, I think it is a message that speakers should be below deck. Most people go sailing for the quiet, and if you are playing tunes in an anchorage--even down low--you will be unwelcome. Underway, knock yourself silly. Also, as suggested by other, mounting them low will help keep the sound on-board and direct the excess upwards.

 

[Bill Roosa]

Shielding magnetic fields

There is no way to shield magnetic fields. Your options are fill the holes, buy new instruments, relocate the compass, buy a remotly reading compass or live with the badly reading compass.
Depending on your sailing area and environment you may not need an ACCURATELY reading compass. If you are an inland or sheltered water sailer what would be the harm in having the compass read wrong? Technically it reads wrong all the time right now. You could gin up a deviation table to get the correct heading from it in any case. You will want to establish if changes in volume also cause an additional change in deviation. You could also incorporate that into the deviation table.
Personnel I don't use the compass to determine a course. The autopilot makes mine read 15 deg off in random ways. I do use the compass to hold a course. Once I line up on a course using GPS or a sighting or pull a course off the chart and use the deviation table to get a compass course i can hold that course just like if the compass is reading correctly. Just keep the (wrong in this case) number under the pointer just like normal. Where is my "that's easy" button?
Now when the GPS crapps out in the fog and you have to change course you have to figure out how you are going to proceed. I'd use dead reconing from my knot meter (properly compinsated for with a table like a deviation table) and watch. I know the new direction from the chart and therefore how many degrees to turn through to get to the new course. I can do the math and turn that many degrees from the compass or just read the desired course from the deviation table. The former method has some risk as the compass will surly have different amounts of deviation in different directions. That can be mitigated by developing a safety angle so you are sure to stay in safe waters.
All this is just good seamanship, having several sources of navigation information (think I read that in a book somewhere)
Since you don't seem to want to install new instriments I'd just note that without any other instriments ALL YOU HAVE IS THE COMPASS!!! that would make me a little leary of going out on anything but a nice day and for only a day trip. Course my sunfish had NO instriments so it really depends on how you use your boat and the risk you are willing to subject your crew to.

 

[Rick D]

Speakers

You may want to research some lines of marine low-interference speakers. There can be a very large difference. When I installed my replacements, I found that some were far better shielded.

 

[zeehag]

can you mount the speakers on the spreaders in stead of in the face of the compass?/ many speakers for stereos are quite strong---if yoy noticed the difference after installation, then , guess what--is the speakers befouling your life. need to move speakers to not do that. proper nav is more important than music whenye are sailing. as much as i love blues and boogie, when i am sailing i hate noise from artificial sources. besides the stereo interferes with ability to listen to the vhf.
when i am anchored, music from spreaders is a blessing. can be heard from bow to stern and only gets messed up if you knock down.

 

[r.oril]

Frank...What did you start here?
Interesting that so many negative things can be associated with speakers and sailing. I have mine setup over the galley and play stuff like Yani, out in the middle of the lake. When I am taking everything down to trailer home I will have the "80's" blasting away. I will be sure to be attentive to my surroundings if neighbors are near.
I have a compass and hand held GPS but can't too lost on Pyramid lake, LOL! If the sun is up and use my Boy Scout training.
All of the responses are very interesting and informative.

 

[Ross]

I have an AM-FM broadcast receiver with a tape player, The speakers are mounted under the starboard settee. But we find it rare that we turn it on, prefering the quiet.

 

[rpwillia]

A positive post in this thread

Frank...What did you start here?
Interesting that so many negative things can be associated with speakers and sailing. I have mine setup over the galley and play stuff like Yani, out in the middle of the lake. When I am taking everything down to trailer home I will have the "80's" blasting away. I will be sure to be attentive to my surroundings if neighbors are near.

R.oril is righ. Since it is cold out perhaps we need to start a new thread about the music we like to play on anchor for our boating neighbors. My personal favorites are:

Red Neck Yacht Club - Craig Morgan
Lunatic Fringe - Red Ryder
Back in Black - AC/DC

It all depends on who is out there. My factory installed speakers on my jump seat are great for getting the tunes out there and drowning out the sounds of the 60' power boats blowing by.

 

[zeehag]

music for at anchor?? i generally listen to blues and good boogie woogie....and i dont usually have the sound up too high unless someone has a noisy genny

 

[Liam]

Be careful playing Yani too loud... you may end up responsible for mass suicides.