Max,
Those compasses are not compasses. They are compass repeaters. The compass is elsewhere on the ship.Please reread my earlier
answer below. Another solution to the hand held swinging dilemma, might be to swing the compass positions where you would take
your sightings and simply create an offset table for each one. This too is common practice.
Steve

"max camirand" wrote in message ...
On Dec 3, 4:13 pm, "Steve Lusardi" wrote:
Max,
This compass issue is real and it is expensive. Here are your choices. magnetic and true. Magnetic compasses deliver a magnetic
bearing referenced to magnetic north. They come in 2 flavors normal and flux gate. Both are influenced by external magnetic
fields
even undersea cables, which can be really exciting when sailing on auto pilot. Of the two, the flux gate is the most reliable on
a
steel boat, as you mount the sender high up on the mast away from local influences and in your case, is the best bang for your
buck. These are NOT primary ship compasses. This technology is yacht or workboat. All magnetic compasses must be swung at
installation and reswung every year. These can be found used, but if you buy used, plan on sending the unit to a compass house
for
servicing and certification. They will need it, especially if you buy from an Indian ship breaker's yard. Gimbaled, flat faced
compasses are available used, but are rare and they are expensive $500-1k. Most cannot be used to take visual bearings. Hand
helds
are you best bet there.

True bearing compasses come in two flavors gyro and now, satellite. Ships under 500 tons require at least one gyro and a
satellite compass as secondary under IMO rules. Ships over 500 tons require two gyro compasses. Gyro systems cost $20k new and
the
gyrospheres need replacing every 5 or so years at $8-10K each. Satellite compasses operate using phase comparison of the carrier
signal and are very accurate, if installed correctly on the centerline. Both deliver a true bearing. Gyro compasses lose
accuracy
above and below the 80th parallel and suffer speed distortion. Satellite compasses cost between $5k and $8k, run on low power,
very reliable, but will lose its bearing under severe storm conditions, however the good commercial ones have internal fluxgates
and inertial sensing chips that perform automatic dead reckoning under signal loss conditions. Used gyros are a bad deal because
most will have duff gyrospheres, use lots of power and are expensive to service. Used sat compasses are non-existent. The
cheapest
new is Furuno, but they won't dead reckon. They have two models, one more accurate than the other. Both affordable. All true
compasses also require repeaters, some are stepper driven, some are differential and others are NMEA 0183. Rotating repeaters
have
a max ROT rating. If you have a small boat that can turn quickly, their ROT rating can easily be exceeded. Older stepper
repeaters
are typically rated around 6 degrees per second and the newer NMEA ones are around 20 degrees per second and electrical resync
buttons The older ones are mechanically reset. The rotary NMEA repeaters are $2500 each new and very very rare used.

I have a CPlath gyro, a Sperry Marine sat compass, a B&G Flux Gate on the mast and a failsafe CPlath magnetic. I have done it
all
and own the T shirt. Bought everything second hand and rebuilt them, except for the Sat compass. I bought that new.
Steve

I'm trying to minimize expense and electricity consumption, so I can't
have any sort of compass that puts a constant drain on the batteries,
as superior as a fluxgate compass may be. Swinging a magnetic compass
isn't a problem.

In your experience, have you found handheld compasses to be reliable
for taking bearings from a steel boat? I absolutely need magnetic
bearings for navigation. My first thought was a flat-faced compass
with a direction finder, like the ones we use on ships. The compass
will be mounted on a steering pedestal and therefore is fairly far
away from the nearest part of the steel hull and deck. The other two
options are a handheld bearing compass or a relative bearing direction
finder on a fixed card (add relative bearing to compass heading to get
compass bearing).

I probably should have asked at the same time... I'm also looking for
a rotator log.

-m