Let's talk compasses

dogon dory · Posted: Wed Feb 20, 2008 1:04 am Post subject:

Sorry, Folks - Post Deleted By Author

hardee · Posted: Wed Feb 20, 2008 2:17 am Post subject:

Don said:

Forty Two · Posted: Wed Feb 20, 2008 4:53 am Post subject:

I see many good suggestions here, but I would add this word of warning. . . . Do not get a Tate's compass.

Because he who has a Tate's is lost.

Grumpy · Posted: Wed Feb 20, 2008 10:03 am Post subject:

One thing to be really careful about in a small boat is the influence of metallic, magnetic or electronic instruments on your compass. We all move "stuff" around the boat fairly frequently.

The fluxgate compass will auto compensate if you do a couple of very slow 360 turns, but a classic magnetic compass will not. All goes down the tubes when you move something anyway.

Try putting you cell phone within 1 ft of the compass and see what happens..
On CD22 you can probably forget any dreams of 1 degree accuracy. Repeatability maybe.

Just my .20 cents worth.

Merv

Robbi · Posted: Wed Feb 20, 2008 10:35 am Post subject:

I wouldn't leave home without a compass. I find for a smaller boat the Iris 100 works great. I have no interference from electronics, and it can be lifted out of the flush mount and used as a hand bearing compass, or stored until needed. It costs about $100.

Robbi

matt_unique · Posted: Wed Feb 20, 2008 11:18 am Post subject: Interference

Grumpy · Posted: Wed Feb 20, 2008 11:54 am Post subject:

Matt, you can see the 5 degree effect just by following a car driver who is on a cell phone

Merv

C-Otter · Posted: Wed Feb 20, 2008 12:55 pm Post subject:

Be sure to position your compass while the boat is in the water, not on the trailer. Very Happy

C-Otter.

DaveS · Posted: Wed Feb 20, 2008 4:19 pm Post subject:

When outfitting "Sea Shift", Les installed a compass that can be "quick released" from its' base mount and then it becomes a hand held compass. This allows me to carry it out into the cockpit, where I can be certain that I am clear of any thing of interference that would cause compass deviation.

(Hence, no deviation, unless I hold it close to the cell phone or numerous pagers and knives that I have hanging off my belt..........of course the steel plate in my head doesn't help much either... Rolling Eyes

)

thataway · Posted: Wed Feb 20, 2008 9:19 pm Post subject:

Dave, You want to compensate the compass/draw deviation tables with the compass in its usual position on the dash. Even in the cockpit, there can be magnetic influences from metal objects--plus there is the problem of how to line the compass up fore and aft accurately. You will be steering with the compass from the location at the helm.

As Dan rightfully suggests a hand bearing compass should be part of the gear aboard. We use a Vion puck type. It has a split prism and reads to a degree--both from above and when sighting on an object. We also use the compass in the 7 x 50 binoculars as a head bearing compass.

oldgrowth · Posted: Sat Feb 23, 2008 2:41 am Post subject:

I have more compasses than a person really needs, but like the American Express Card man on TV, I never leave home without one.

I have a Ritchie Compass that was on my boat when I purchased it. For it’s size (I am guessing it has a 3 or 3 ¼ inch dial) it is somewhat inaccurate with 5 degree markings but adequate for a boat. It’s probably accurate to within 1½ degrees.

The two hand held sighting compasses I have is a Suunto with a 2¼ dial and capable of a 1 degree accuracy. The other is a Steigung with a 2½ inch dial capable of a ½ degree accuracy. Neither one would be much more accurate than the Ritchie compass on my boat. You need a stable platform to read with that kind of accuracy and a boat is not, except in dead calm water.
________
Dave

matt_unique · Posted: Sat Feb 23, 2008 8:13 am Post subject: Backup