I was having problems with the helm compasses we have on-board. They had been newly installed at the Southern Wind shipyard in South Africa and I’ve experienced trouble with both of them while sailing in the Caribbean and Europe. However, they had worked just fine while I was in Cape Town, why? After some research I discovered the answer.
As a sailor, you know all about magnetic deviation and declination and understand how to take them into account for navigation. However, have you ever heard anything about compass zones? Neither did I until I spent some time researching the problem I was having.
Specifically, the compass card was getting stuck once in a while for no apparent reason. Striking the top of the compass lightly with my hand would free up the compass card and it would then swing to the correct location. I thought the needle bearing was worn or something so I decided they both should be changed.
Looking for a replacement I scoured the web and reviewed the products on the Suunto and Silva websites however they had very few marine compasses listed. Finally, I found the Richie Navigation company website and learned they had the largest selection of marine compasses to choose from. After examining all the different models I spotted one labeled a ”Global Compass”. When I looked at the description for the compass they had a link to some information about “compass zones”.
The issue to be solved is that the further south you are from the North magnetic pole, the more the compass card has to 'dip' to accurately point at it (think about the curve of the Earth). While the needle and compass card can handle quite a bit of dip; a compass constructed to be used in South Africa, for example, has to be able to handle more 'dip' than one constructed for use in Northern Europe where it is closer to the North magnetic pole.
The compass installed by the shipyard was purchased in South Africa so it was assumed to be for a boat used down there. By the time I reached the Mediterranean, the compass card was trying to 'dip' too far for north and became hung up trying to do so.
Ok, so now I knew what the problem was... How to fix it? As it turns out the service department at Richie Navigation came up with the plan to provide me with a compass set up for zone 2 and a replacement compass module for zone 5. The compass would work fine while we were in zone 1, 2 or 3 and when we crossed into zone 4 we’d replace the compass module with the one for zone 5. Then we’d be OK in zone 4, 5 and 6 until we passed above the equator again later in our circumnavigation.
A great solution that has been ratified as we had started our circumnavigation in Europe last November and now (April) have arrived at the Galapagos Islands where we’ve changed the module to the one for zone 5. Everything is to be working perfectly.
So, one baffling problem gets solved and I learned something about compasses I didn’t know before. So, when you are preparing for your next circumnavigation, now you know how to make sure your compass is working correctly no matter where you are in the world.
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Comments so far
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Art
on May 8, 2015
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Roland
on May 7, 2015
Hi Art,
Great article.
This was not an unusual question I got from customers when they arrived in the southern hemisphere. "Why is the compass tilting?"
Later we changed to Suunto. They claimed it was setup both for southern and northern hemisphere. Bella has one. I guess we have to sail over there to see if it works!
Thanks Roland, an interesting research lesson for me! I did look into the Suunto and Silva website but they have so few offerings for helm compasses that would fit my console that, once I found Richie, I decided to work with them on a solution for me. Will be interesting to see how your compass stacks up when you get out of the European zone 2.