Compass error due to close proximity of VHF radio

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davidmh

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I need to find a position for a hand held VHF close to the helming posistion on a 28ft yacht with tiller steering, the compass is mounted on the aft coachroof bulkhead. The manufactures state the compass safe distance is 1metre. That distnce is difficult to find, I can find suitable positions about 400 -500 mm distance. I single-hand a lot so need to be able to grab the VHF without leaving the tiller.
Question for the forum is
How much error would be made at 400mm distance, would it be significant, would it change if the set is On or Off
Would the error vary depending on the ships course (N S E W)
Would value your opinions.

David MH
 
It will induce an asymetric error in the compass, which msy not be too severe
Do you not have a GPS which will give better course direction and be far easier to read
Some hand held VHF s have a built in GPS.
 
I would suggest simply putting the VHF near your compass - move it back and forth, turn it on and off - and see if the compass card moves.

Re using a GPS to give heading... that is a seriously big NO and will only lead to tears. Your GPS will give COG - with lag - and not heading.

The ' safe distance of 1 metre' is an ' industry standard '. I've never seen one that says 'safe distance 73 centimetres'
 
My chart plotter is very close to the compass. Before installing the plotter I moved it around the compass and the compass never moved.

My handheld VHF did affect the compass if it got within a foot or so, and I have found that glasses and especially the snap shut glass cases cause problems.
 
On my slightly smaller boat I have a similar situation. I found that if I put the handheld VHF on the bulkhead on the compass side, or on the bench at the bulkhead end on the compass side, I get easily noticeable (and seriously problematic) compass deflection... and if I put it on the other side I don't. I think my usual position ends up over a metre away, but the distance at which it doesn't really cause me any problems seems to be less than that. I don't believe there's a hard cutoff.
 
davidmh said:
I need to find a position for a hand held VHF close to the helming posistion on a 28ft yacht with tiller steering ...
Would value your opinions. ...
Click to expand...

Do you need to find a position that is that close? For decades I sailed without a handheld compass and with a fixed VHF a lot further than 1 meter from the helming station. Perhaps this is a problem that can be easily resolved if you mount the hand held further away in the cabin. It may be possible to use a speaker extension where the distance to compass is less stringent.
 
As far as I know it's the speaker magnet that causes the most deflection, so I wouldn't have high expectations for a speaker extension doing much better tham a handheld. That said, I did ponder wiring a waterproof extension speaker for fixed VHF to the transom under the tiller, pointing forward. It ought to beat the handheld for the routine listening watch while being as far as possible from the compass. I haven't actually done this.
 
justanothersailboat said:
As far as I know it's the speaker magnet that causes the most deflection, so I wouldn't have high expectations for a speaker extension doing much better tham a handheld. That said, I did ponder wiring a waterproof extension speaker for fixed VHF to the transom under the tiller, pointing forward. It ought to beat the handheld for the routine listening watch while being as far as possible from the compass. I haven't actually done this.
Click to expand...
Some speakers are magnetically shielded for this very reason, unlike the handheld VHF speaker where space is at a premium, but more likely it something else in the handheld VHF that impacts the compass, as the speaker is very small. Worth researching the distances by checking the OEM manuals, if possible.

The process, home made shielding.

 
Interesting, thanks. I think a lot of compact modern devices use very strong speaker magnets for loud sound in small packages - phones certainly do. Current consumption in a VHF seems small enough to be unlikely to make much electromagnetism except perhaps when transmitting on high, and as it still deflects the compass when off, the speaker remains high on my list of suspects.
 
My compass is mounted port side of the cockpit on the bulkhead whilst my handheld lives just inside the cabin on the bulkhead to the port side. I fixed a small wooden tray there which it lives in. Easily reachable form the tiller on my boat. Never measured it but guess they are about a 1m apart.
Interestingly enough some years ago I was sailing on a compass course across to Ireland from N Wales with my portable radio on cockpit seat listening to the test match special. Play ended so I switched the radio off and on moving the radio to stow it below noticed a swing of the compass needle probably about 10degress. Whoops I thought - had to alter course and have been careful ever since. So yes compass is a thing to watch out for.
 
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Thanks for all your replies, I agree with much of the comments. Nice to know that 1m is the industry standard. I have heard from Icom who made the unit and the magnetic content of the unit is the magnet in the speaker. I will just put it somewhere and watch the compass. For coastal sailing the advent of the chart plotter means that you are usually checking the course on the plotter and adjusting the course by a few degrees as required. The plotter gives you COG which is what matters, the ships head is rarely the same as the COG. When i find out the compass error I will make a note of it if it is significant.
Davi MH
 
A neighbour said that he thought his steering compass was inaccurate so I went to check it against my hand bearing compass. It was out by about 30 degrees. I noticed he had fitted a large cockpit speaker next to it.
"I think that's your problem".
"Oh but I must have music".
On another boat the skipper was getting wildly different hand bearing readings to me. He had just got a pair of specs that could split and were connected with a powerful magnet at the nose.
 
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