Cautionary compass tale

[Cat-a-tonic]

Had an interesting experience with my compasses recently. The main ship's compass leaked and the card toppled so I replaced it. Luckily the latest version still fits the old holes so easy job (Plastimo Contest 101). To calibrate it I used my hand bearing compass (Plastimo Iris 50) but soon realised that the bearing was adrift by up to 20 degs. Did lots of sighting on known bearings and convinced myself the hand bearing compass was also faulty. So bought a new one but comparing the old and new Iris 50's gave the same results. Checked against noon sun (actually 12:09:19 for corrected sun's noon for my position). They still seemed way out. However I put them on the ground against a stick's shadow and, bingo, spot on - due South. Back up to my eye - 20 degs out. Light bulb moment - it's my new spectacles - enough metal to affect the compass. Sorted and the new ship's compass can be calibrated with confidence - new plastic specs for sailing in future.

[SV Bacchus]

Very interesting, good info to know. Thanks!

[Kim Gregory]

This problem can be REALLY bad if you have the magnetic 'clip-on' sunglasses!

[dangerfield55]

I needed to have my autopilot replaced. Done professionally by a person I really respect. My ships compass is now 25 degrees off. The drive was changed from the right side of the wheel to the left. He says he has done this before and no one noticed a problem. He thinks they never checked their compass. The plan is to put the unit back on the other side.