Times, they are a changin' (or are they?)

[qsiv]

Re: Just how many people have had their compass swung?

I try to redo mine every season - I tend to do it myself (I dont usually fiddle with the correctors as I dont feel entirely competent), but at least the deviation card is reasonably up to date.

An easy to use piece of software can be found at pangolin[url]

They do explain all the theory, and how to perform the corrections - mine has always been small enough to live with.

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[Sybarite]

Re: Times, they are a changin\' (or are they?)

I inherited a deviation card that showed a max of 3°. Nobody on the boat can steer constantly to that precision.

When I head on a long crossing I check ( for the course I am taking) the fixed compasses with the bearing compass - not affected, at least, not to the same extent, by deviation - and double check it with the GPS. (Remember to take metal frame glasses off when using the bearing compass).

You then know for that heading (or those headings if you have to beat to windward) what your realistic deviation is.

All the recent checks indicate that the original deviation card is still valid. In calculating my courses I usually ignore it as the other influences - tides, leeway compass variation are collectively normally much more important.

This has worked for me including several DR crossings in the Med and from Britanny to Scilly in pre GPS days.

John



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[Twister_Ken]

PS on compass swinging

Missed Alderney once, in pre-GPS days when I was ferrying a cruiser racer down to St Malo for the owner to take off on the family cruise. My nav is not normally that bad, and the other lads on the boat were all capable of steering a good course. Much fiddling with the DF established sort of where we were, and we steered the rest of the way using the h/b compass. We knew the boat and we knew the compass was reliable. When we got to St Malo we tried to check the compass on various transits but could find nothing amiss. Told the owner who was good at those sort of things. He immediatley started looking for what was different from normal. Answer, an outboard clamped to the stern rail, about 3 feet away from the compass. But, when the boat was flat it had minimal affect. He wondered if the problem was to do with the vertical position of the o/b when the boat was heeled (it had been a one-sided beat across). So we lifted the outboard a couple of feet in the air and a little closer to the compass, which promptly swung by about 25 degrees.

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[peterb]

Specs

Careful. It may not be the spectacle frames that are the problem. I had one pair on which I finally traced the problem to the little screws that clamped the frames round the lenses. Some opticians use magnetic screwdrivers to hold them while they are tightened.

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