Two compasses, why?

Most of my time is spent doing sight-based nav or sailing to the telltales. If I'm passage-making, the boat tends to be on auto anyway.

What would you do if you were on another boat without a plotter? Not a nag, just askin. Say, you had taken up a charter with some friends for a week in Greece, for example?
 
"one in each of the three iPads and two iPhones."

Do not trust the iPhone compass. Or if you want to have some fun go to the pub with a few other iphone owners and put them all on the table for a variety of different Norths
 
But note that multiple compasses must be mounted far enough apart that their magnetic fields do not interfere.There is a story about a skipper with novice crew who kept seeing random errors in his compass reading. He asked the crew if anyone had anything magnetic; no-one did. On effectively frisking them a pocket brass compass was discovered; "but it is brass, not magnetic!".Mike.
My tiller pilot started giving random changes of course and I realised it was changing as I moved around the boat. The culprit turned out to be my favourite German army knife (Victorinox, but with green plastic instead of red), which had somehow become a strong enough magnet to affect the TP from a metre away. I'm still trying to work out how that happened
 
Someone couldn't work out how, every time he shot a string of pots on auto the boat steered a curve. The AP compass was under the deck, the steel framed pots stacked above it.
 
I often thought there was a minute course change passing Mullion N-S. there is a major geological fault running E-W from Polurrian cove, where students are taken to view the difference between the cliffs on either side.
 
Of course you were. Indubitably. Incontrovertibly, even.

So we could really bore the pants off the Solent Circumcisioned on 'ere by rabbiting on about Fourier Analyses of Residual Swings, differing forms of construction of Most Probable Position, collimation of periscopic sextants ( air and other ), and Grid Navigation Based on a Nominal Start Point.

Or just get another round in...... :rolleyes:
 

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