bilbobaggins
N/A
From a friend.....
"I have just narrowly avoided an attack of the 'Wheeltapper's Hammer' syndrome while trying to swing a new steering compass, a conventional Plastimo bought and installed here in Auckland. The differences between it and the simple hand bearing compass I was using as a reference were quite alarming - not only large, but also inconsistent. To cut a long story short, it was the hand bearing compass that was at fault. It had been fine back in UK, but in these southern latitudes the card tilts dramatically and fouls the inside of the case. A new one bought here has no such problem.
Problem solved, but this does prompt a question as to how far south of the equator it was necessary to sail before this symptom might have first appeared (I flew here direct from UK, so can't throw any light myself). I assume the misalignment gets steadily worse as latitude increases southward, but is there a gradual degradation in performance, or is all more or less OK until a critical point is reached at which physical interference triggers total unreliability? And how far north of the equator on the homebound journey might the 'Southern Hemisphere' Plastimo steering compass be usable? Is the problem there at all in such larger instruments, or is it just confined to small hand-helds? What does the theory say? And what does experience tell us?......"
When last did we give the compass a 'sideways look'? Compass calibration remains a professional task, mandatory for Small Commercial Vessels ( and large ), yet most yot owners consider that 'if it ain't obviously broke, don't fix it'. Do we still presume that the steering compass is spot-on, 'cos it was expensive - and the handheld of unchallengeable accuracy, 'cos some RYA bloke said so?
BTW, the author of the quote is a hugely-experienced pro nav, carrying out a routine check and calibration swing before an ocean passage.
/forums/images/graemlins/wink.gif
"I have just narrowly avoided an attack of the 'Wheeltapper's Hammer' syndrome while trying to swing a new steering compass, a conventional Plastimo bought and installed here in Auckland. The differences between it and the simple hand bearing compass I was using as a reference were quite alarming - not only large, but also inconsistent. To cut a long story short, it was the hand bearing compass that was at fault. It had been fine back in UK, but in these southern latitudes the card tilts dramatically and fouls the inside of the case. A new one bought here has no such problem.
Problem solved, but this does prompt a question as to how far south of the equator it was necessary to sail before this symptom might have first appeared (I flew here direct from UK, so can't throw any light myself). I assume the misalignment gets steadily worse as latitude increases southward, but is there a gradual degradation in performance, or is all more or less OK until a critical point is reached at which physical interference triggers total unreliability? And how far north of the equator on the homebound journey might the 'Southern Hemisphere' Plastimo steering compass be usable? Is the problem there at all in such larger instruments, or is it just confined to small hand-helds? What does the theory say? And what does experience tell us?......"
When last did we give the compass a 'sideways look'? Compass calibration remains a professional task, mandatory for Small Commercial Vessels ( and large ), yet most yot owners consider that 'if it ain't obviously broke, don't fix it'. Do we still presume that the steering compass is spot-on, 'cos it was expensive - and the handheld of unchallengeable accuracy, 'cos some RYA bloke said so?
BTW, the author of the quote is a hugely-experienced pro nav, carrying out a routine check and calibration swing before an ocean passage.
/forums/images/graemlins/wink.gif
