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Old 14-08-2015, 11:51   #1
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Hand Bearing Compass - compensation for dip angle

I find that when I use a compass that I bought South Africa (where the magnetic dip angle is up) in northern latitudes (where the dip angle is down) that the compass card seems to be pulled down on some bearings so that the gradations and numbers become difficult to read in the prism viewfinder. (It's Hockey-puck type of compass) Because of this behavior, I've assumed that the compass was designed to be used in southern latitudes, and that I should buy another compass for use in northern latitudes.
However when I try to buy a compass, I have not been able to find any information that allows me to specify the area in which I plan to use the compass.
Can anyone shed light on this topic.
Thanks,
-m-
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Old 14-08-2015, 16:47   #2
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Re: Hand Bearing Compass - compensation for dip angle

What you speak of is true although my memory is not cooperating at the moment as to the term. I spent several decades as an exploration geologist using a specialized compass made by Brunton. I will take the liberty to think you don't want to spend $700+ USD for a handheld compass. When ordering you had to specify Northern or Southern Hemisphere. Depending on choice they put a tiny counterweight on the needle. If needed you could always send it in to change it.

What I do think is that if you purchase a marine handheld compass it comes precompensated for the area you bought it in. That is, buy one south of the equator it's compensated for that hemisphere and vice versa.

It's an interesting question. I would look forward to any response from world cruisers. For example, which would you use near the equator ?

Thank you for the question
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Old 14-08-2015, 16:57   #3
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Re: Hand Bearing Compass - compensation for dip angle

Its magnetic dip or sometimes magnetic balance. There are 7 zones around the world but sometimes only 5 (or even 3) are catered for.

Here is a simple link but google has many more

http://www.silvacompass.com/uploaded...nation1_lg.gif
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Old 14-08-2015, 17:01   #4
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Re: Hand Bearing Compass - compensation for dip angle

BTW, welcome aboard Mulangi,

It is possible to have the needle re-weighted by usually not worth the expense of cheaper units. Distributors usually distribute the "right" compass to retailers in any given location.
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Old 14-08-2015, 17:35   #5
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Re: Hand Bearing Compass - compensation for dip angle

If you buy one in Europe or North America I am sure it will be suitably compensated for the northern hemisphere...
The smaller the card the greater the problem , 'large card' magnetic compasses on big ships aren't affected ( leaving out discussion of horizontal component etc in V High latitudes etc). The ( European bought) Plastimo in my boat shows a far bit of dip but still works, once had a 'northern' puck... unusable in the southern 'middle' latitudes.

Don't chuck your old one.....
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Old 15-08-2015, 00:57   #6
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Re: Hand Bearing Compass - compensation for dip angle

Yep, we have two hockey puck HBCs aboard, both purchased in the California marketplace, and both quit working at about 20 deg south. Our main steering compass, a pretty good Danforth binnacle model, started hanging up when we neared New Zealand and required re-balancing.

oh, the things that they don't tell you at the boat show...

Jim
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Old 15-08-2015, 09:18   #7
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Re: Hand Bearing Compass - compensation for dip angle

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Originally Posted by Jim Cate View Post
Yep, we have two hockey puck HBCs aboard, both purchased in the California marketplace, and both quit working at about 20 deg south. Our main steering compass, a pretty good Danforth binnacle model, started hanging up when we neared New Zealand and required re-balancing.

oh, the things that they don't tell you at the boat show...

Jim
Exactly. I'm in Canada. I have a Ritchie Globemaster at the helm, which I expect will be OK until about Fiji, and will then require servicing, but my Silva and Plastimo HBCs will need to be traded to someone headed North, I think.
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Old 15-08-2015, 11:03   #8
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Re: Hand Bearing Compass - compensation for dip angle

Small compasses are indeed weighted according to the expected dip, vertical component of the earth's magnetic field, in the area sold.

Larger compasses are less likely to bind up as the greater weight of the magnet assembly is below the pivot point.

'Proper' marine compasses include a vertical magnet suspended below the compass to compensate for both dip, and any vertical magnetic fields below the compass, from the vessel, the engine, or a steel hull. (Heeling error).
In a yacht with the steering compass above the engine, and 20 degrees of heel, heeling error can be significant. A likely cause of all those yachts hitting the Taumotu reefs pre GPS.
The correcter magnet is moved further away from the compass as you approach the magnetic equator and reversed when you change magnetic hemisphere.
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Old 15-08-2015, 11:25   #9
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Re: Hand Bearing Compass - compensation for dip angle

Quote:
Originally Posted by Jim Cate View Post
...oh, the things that they don't tell you at the boat show...
Jim
Wow you learn something everyday.
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Old 15-08-2015, 12:19   #10
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Re: Hand Bearing Compass - compensation for dip angle

Thanks for posting a good question. I never even thought of that.
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Old 15-08-2015, 13:00   #11
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Re: Hand Bearing Compass - compensation for dip angle

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Originally Posted by Jim Cate View Post

oh, the things that they don't tell you at the boat show...

Jim
Remember, there is a good chance that the people stuck with (or hired for) boat show duty do not even know, so it is not just "don't," it is more like "can't."
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Old 15-08-2015, 13:18   #12
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Re: Hand Bearing Compass - compensation for dip angle

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Originally Posted by KJThomas View Post
Small compasses are indeed weighted according to the expected dip, vertical component of the earth's magnetic field, in the area sold.

Larger compasses are less likely to bind up as the greater weight of the magnet assembly is below the pivot point.

'Proper' marine compasses include a vertical magnet suspended below the compass to compensate for both dip, and any vertical magnetic fields below the compass, from the vessel, the engine, or a steel hull. (Heeling error).
In a yacht with the steering compass above the engine, and 20 degrees of heel, heeling error can be significant. A likely cause of all those yachts hitting the Taumotu reefs pre GPS.
The correcter magnet is moved further away from the compass as you approach the magnetic equator and reversed when you change magnetic hemisphere.
You're explaining all the "stuff" that exists inside our large skylight compass topped binnacle. Our boat was built in 1931, the tall binnacle in front of the wheel has a nice (60's-70's era) Richie compass in the skylight and below that has about a hundred little shelves around the perimeter inside the wood binnacle for flinders bars and whatnot. I unlocked the door one day, took a look at all that and slammed it shut, said a prayer and hoped I'd never have to mess with it! It looked...complicated...

The compass adjustment is perfect for the SF Bay area at present. South or North we make small (or large) notes of adjustments. Only in Alaska did we really note that we were...off...and some of that was due to local magnetic disturbances (noted on the charts). If we venture far to the South, like others, we'd have to adjust the correcting bars (or have them adjusted) for sure.
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Old 15-08-2015, 13:38   #13
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Re: Hand Bearing Compass - compensation for dip angle

FWIW, we had ours re-compensated in Auckland. It can be tricky finding someone with the skills to do it.

Ann
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Old 15-08-2015, 13:54   #14
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Re: Hand Bearing Compass - compensation for dip angle

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Originally Posted by S/V Alchemy View Post
Exactly. I'm in Canada. I have a Ritchie Globemaster at the helm, which I expect will be OK until about Fiji, and will then require servicing, but my Silva and Plastimo HBCs will need to be traded to someone headed North, I think.
FWIW, during the passage in which our Danforth compass had the dip angle problem, a friend who had a Ritchie compass noted that the card tilted strangely, but did not hang up and cease working as ours did.

Our current boat also has a Ritchie binnacle compass, and in the hands of the builder/PO went as far north as the Aleutians with out failure, and works fine as far south as 43 degrees (our personal furthest south). So there seem to be some differences in design that influence this performance over wode ranges in latitude (and dip angle0.

Jim
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Old 15-08-2015, 15:06   #15
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Re: Hand Bearing Compass - compensation for dip angle

I think you're all taking the piss. Magnetic flux lines are essentially parallel to the earth's surface, except when close to the poles. Unless you're an extreme sailor, it should not matter much.
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