NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Compass Checks at Sea
From: Jeremy C
Date: 2008 May 23, 15:49 EDT
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From: Jeremy C
Date: 2008 May 23, 15:49 EDT
In a message dated 5/23/2008 6:57:37 P.M. West Pacific Standard Time,
george@huxtable.u-net.com writes:
Jeremy's mailings have provided several interesting surprises, to me.
One is the frequency of checks made on the gyrocompass, once per watch.
Presumably, there's much cautious overkill in those arrangements. Otherwise,
how would ithe navigation cope with a prolonged period of cloudy weather,
when no such checks are possible? Does the navigator get uneasy under such
conditions, and if so, after how long? Might he then revert to
cross-checking against the magnetic compass, with all its known
deficiencies?
Captains dictate this in standing orders. It is mostly to have
copious records in the event of a casualty. I think in part it is to keep
the mates busy and on their toes during a long sea watch. If there is
prolonged cloudy weather, then it is done when a body is available. There
is little consternation about this as long as the log entries dictate that there
is inclement weather and the gyro matches the corrected magnetic compass for the
most part. Cross checking the magnetic compass with the gyro, on my watch,
is done at least hourly and certainly at any and all course
changes.
Another surprise, at first sight, was the use of Polaris for checking
azimuths. In our waters, we would never even consider that, Polaris being 50
degrees up in the air. But for denizens of the Northern tropics, of course,
Polaris is a nice low star for such purposes, always in place.
This is done because most mates do not have the ambition to do the HO 229
triple interpolation that is usually the only way they know, as most really hate
Celnav. Some actually learn how to use computers or calculators which then
brings about the problem of actually identifying an alternative star. Most
mates just aim North, manipulate the mirror and take a sight. The last
time I navigated in the middle-latitudes, I remember shooting Polaris
several times with an elevation of about 40 degrees or so and had no trouble
shooting it. In the tropics it is, as you point out, very easy to find and
shoot.
Another surprise, in the first exercise, was his mention of a vessel
drifting. To me, merchant vessels are either travelling purposefully, under
way on passage from A to B, or they are in harbour, never adrift. That led
me to suggest that the exercises might be, to some extent, contrived ones,
and it was refreshing to be assured that no, they would be real-life.
George.
The first exercise was an attempt to eliminate the issues associated with
taking LAN while moving, and thus make it easier. Do merchant ships
"drift?" They most certainly do, and more often then you would
think. The most common reasons for this are mechanical breakdown
and waiting outside a harbor for a pilot. I have spent many an hour
on the bridge drifting because of the former on one of my old ships.
Jeremy
Get trade secrets for amazing burgers. Watch "Cooking with Tyler Florence" on AOL Food.
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