Friday, October 6, 2006


Compass, 10/6/2006

A barely functional compass makes navigation a bit... challenging. A compass has one job: point to Magnetic North. Our flybridge compass had virtually no fluid, so it didn't do it's job very well. A compass can be repaired, but ours was in pretty bad cosmetic shape too, so I installed a new one.

Installing a compass isn't as easy as you might think, either. The compass has to be aligned very carefully with the keel of the boat, or the "lubbers line" won't tell you your true (er... magnetic) course. Plus, a new compass requires compensation. No, you don't have to pay it a salary -- not that kind of compensation. I'm talking about making adjustments to the compass to compensate for ferrous metal on the boat that might cause inaccurate readings. It's a challenging problem. Ritchie Navigation has a good description of the compensation process, but if you're really interested in the amazing history of such a "simple" device, read Gurney's book, "Compass: A Story of Exploration and Innovation". Incredible!

Our 20-year-old compass was a Ritchie, model HF-72, no longer in production. The replacement model, HF-742, allegedly includes a retrofit adapter so it can be installed easily in the old location. Ah, but I should know better by now, it's never that easy. The adapter didn't quite fit either, so I ended up having to patch the original mounting holes and drill new holes in the right places. In the end, though, I successfully navigated my way through another project, and learned a lot about this magnificent instrument along the way.

1 comment:

Brent said...

So is that the procedure you actually used to compensate? I had the same issue when I replaced mine, but got lazy and just ran with my GPS on for a while to see how far off the compass was from the GPS.

Then again, I am not nearly as adventurous as you and stay inshore.