TomCat 255 Magnetic Compass

gcharlie · Posted: Sun Jul 16, 2006 8:00 am Post subject: TomCat 255 Magnetic Compass

What's the best location for the main magnetic compass and what has been been your experience with magnetic compass deviation on the TomCat 255?

We'll have lots of DC electronics clustered around the helm, a radar arch, and a roof-mounted SeaMach air conditioner.

Alok and I are partners on a new TomCat 255 scheduled for delivery in September. We're both in the Houston-Galveston Bay area.

MichaelOnTheClaraMae · Posted: Tue Jul 18, 2006 8:05 am Post subject:

It is always a conflict with electronics. You need the compass where you can see / use it but with today's stuff, there is always some kind of electronic interference close by.

With the boat on the trailer or secured in a slip, I would place it in the best location for use with all of your stuff off. Then one by one, turn your electrical equipment on and note any deviation. With any luck, you may find the effect may not be great enough to warrant placing the compass in a useless location.

Bob Cat · Posted: Tue Jul 18, 2006 9:37 am Post subject:

I installed mine in a spot directly above the wheel on the sloping surface. Excellent visibility. I'm sure there is some deviation when I have all the electronics on, but it doesn't appear to be anything radical. Anyway, I generally steer with the gps/plotter or the autopilot. If these have failed, I'll turn them off and refer to my compass and chart. The other big factors would be the wiper motors and radio speakers, neither of which seem to have much affect. I'll put a pic in the album later today.

Bob Cat

Sawdust · Posted: Tue Jul 18, 2006 11:55 am Post subject:

If you are going to use the compass as a primary nav tool I'd recommend a remote compass. If you install the autopilot, the remote for it works fine - and stable. In the foggy, foggy NW here I like an accurate compass and couldn't find a good place on the dash of my TC24 to get away from all the electronic gremlins.

Dusty

Dora~Jean · Posted: Tue Jul 18, 2006 12:02 pm Post subject:

I was surprised to find out that my Blackberry (compliments of work..) when placed anywhere on my dash greatly affects my center-mounted compass. It's heavier than most cells, color screen, keyboard. It now has a new location.

Dreamer · Posted: Tue Jul 18, 2006 12:45 pm Post subject:

Dreamer's compass, an Azimuth 1000 Fluxgate, is mounted on the center line of the boat in the "dash" area. In two slow 360 turns, it senses all interference and adjusts for any it finds. It seems dead on correct. If you wish to have the display facing you, that can be programmed in to it. Since I eliminated the NMEA multiplexer and wired the compass output direct to the E-80 display, Everything works perfectly. Very Happy

thataway · Posted: Fri Aug 18, 2006 12:21 pm Post subject:

My logic (or lack of): If you loose the electronics --lets say a lightning strike--you will loose the Electronic compass. I always carry a hand held GPS, hockey puck hand bearing compass and hand held VHF in a steel box (Faradey cage so to say). On the other hand, most of the time I steer by the GPS/chart plotter, and rarely watch a magnetic compass (but I have plenty of experience!)

I took my hand bearing compass, before I had put any of the electronics aboard and stood in the center of the boat--and made a sight. Then a fashioned a block of King Starboard to convert the convex top of the dash to a flat and level surface under the compass mount. I then mounted the 3 2/3" compass precisely fore and aft, with the same reading as the hand bearing compass, and didn't worry any further. I will have two GPS/plotters, two VHF radios, innumberable guages, probably a sterio speaker and a fan withing 30" of the compass.

When everything is in place and running, I will swing the compass, using a sun compasss and Azmuth of the sun for the first time. (http://www.ascscientific.com/suncompass.html) I will compensate the compass as best as possiable and construct a deviation table for day running and for night running, with all electronics on--and that will be it.

Peroidically I will swing 8 points with the Sun Compass and check--to be sure that it is not way off. This type of technique got me across a number of oceans long before GPS, so I figure it will work with 4 gPS recievers, a Fathometer and Radar!--plus all sorts of maps I could not immagine 40 years ago!

Do the best you can, make a deviation table and dont sweat it! One other way to check your compass is to run known ranges. I prefer to use fixed land marks, not bouys, since currents can swing these off position signifantly.

There is a place for a compass, since most GPS do not read correct direction when at rest--and that is as you first begin to move away from a dock or objstrucion. With low visability, the compas bearing gets you pointed in the correct direction. It is always a good idea to write the compasss bearing out of a cove, just in case you have to suddenly leave.