compass for autopilot on a steel boat

[Kater]

Thanks for all the replies so far!

It's good to hear that many have good experiences with compasses relatively close to a steel deck. This weekend I'll go and try to measure with a hand compass the deviation on various places onboard to see what would be the best spot. The compas I'm aiming at also has an automatic correction, involves going in circles, like mentioned above. So, if the deviation I find isn't to bad, it should be correctable relatively easy.

Now I only have to make a good, waterproof, mounting. And find the best spot. Maybe on a pole on the stern, maybe at the back of the mast under the boom.

Thanks, all.

[Omatako]

I believe that the fluxgate can be calibrated to ignore the magnetism of the boat itself but that care must be taken when mounting it near soft metals. And soft metals means cast iron for one (the balls referred to earlier in the thread are made of cast iron) and the engine in particular. Apparently whenever the engine is run, the magnetic values around it change whereas the magnetic values of the hull do not.

When I bought my present boat (not steel) we had a heck of a time trying to get the AP to steer an accurate course. We eventually called in a Raymarine guru who tracked down the fluxgate compass to the engine room. When the laughing stopped, he relocated it to the stern cabin and it has been perfect ever since.

I must say though that these things are more sensitive than I thought. My wife put a piece of clothing into a drawer alongside the fluxgate and it had something metal in one of the pockets and the AP was distinctly unruly until we found it.

Andre

[sailingdog]

Putting a fluxgate compass in the engine compartment or near drawers whose contents may change to contain something that can throw off the calibration of the fluxgate compass is a bad idea.

One time we were out and having some trouble with the autopilot... but only on starboard tacks... because a flashlight would roll close enough to the fluxgate compass on a starboard tack to throw it off... it was one of those flashlights that you can "shake" to generate electricity...which turns out to have a pretty large magnet in it to generate the electricity with.


P.S. This was not my boat... it was a friend's C&C 38. So, yes, the heeling was an issue.

[peikenberry]

Some one mentioned the Metal Boat Society. Here's the link. Metal Boat Society :: Index

Probably a fluxgate compas would be what you need, and as everyone has said compasses do work on steel boats. A magnetic compass has to be swung, that is adjusted for deviation, but as someone said it's an annual exercise, a pain in the butt, but necessary. Magnetic deviation - Wikipedia, the free encyclopedia

[Plumper]

I had some issues with my fluxgate location as well. It turns out that the crew liked to throw their life jackets in the same spot and every once in a while something made of a ferrous metal would make its way up there and cause me some grief.

[sailingdog]

Rigging knife probably...

Originally Posted by Plumper

I had some issues with my fluxgate location as well. It turns out that the crew liked to throw their life jackets in the same spot and every once in a while something made of a ferrous metal would make its way up there and cause me some grief.

[Boasun]

Sperry puts out a good 7" magnetic compass that can be mated with a auto steering system.
You will need to have a professional compass adjuster to do the compass corrections for you and develop the Deviation card that you will need.
The compass adjuster is paramount for any vessel in getting any compass properly adjusted. This goes without saying. Unless you have an upper level license and have learned how to generate a Deviation card yourself.

[Valiente]

Originally Posted by Kater

Thanks for all the replies so far!

It's good to hear that many have good experiences with compasses relatively close to a steel deck. This weekend I'll go and try to measure with a hand compass the deviation on various places onboard to see what would be the best spot. The compas I'm aiming at also has an automatic correction, involves going in circles, like mentioned above. So, if the deviation I find isn't to bad, it should be correctable relatively easy.

Now I only have to make a good, waterproof, mounting. And find the best spot. Maybe on a pole on the stern, maybe at the back of the mast under the boom.

Thanks, all.

Hi, Kater! Congratulations on your good taste in boats.

I have several compasses aboard, and they are functional in different ways.

The helm compass, mounted on the steel deck, is a Richie Globemaster with the soft iron compensators. Very manly, too. I have to be careful about putting a hammer down beside it, however...it's obviously attuned to its immediate magnetic environment, and doesn't like metallic interlopers. Beautiful instrument, however.





I also have a KVH AC-103 fluxgate compass, with the sensing head mounted on the aluminum roof of the pilothouse. Compared with the GPS, the Globemaster's bearing (corrected for variation) with a known bearing from a nav aid to a shore marker, the GPS, fluxgate and Ritchie all agree. The fluxgate can be used to feed information to an autopilot, or most autopilots have a fluxgate you can buy separately.

There is a small teak pad on the lower port spreader that I suspect was the home of a previous compass sensor.

I, too, do not yet have an autopilot, but in addition to a wind vane, I am going to get one to drive my hydraulic steering. I plan on getting a ComNav model, probably the simple and straightforward 1001 model:



but I plan on hooking it into a relatively new technology called a Vector G2 GPS Compass, which I will mount atop a hard bimini frame:



Lastly, I have a Suunto Vector "watch" (it does a lot of stuff) that has a remarkably accurate bearing compass function.



Naturally, I've tried it on the aft deck of the steel boat (where my sailing helm is) and it didn't work well at the usual chest height at which watches are read.

However...when I raised my arm to roughly throat level (or five feet off the deck, as I am six feet tall), the compass steadied and gave proper readings. So there may be a number of options that don't involve poles or spreaders for the fluxgate you'll eventually want...if you have a non-ferrous pilothouse or bimini, it may be a matter of just testing until you find a spot unaffected by the boat. I would suggest you consult a pro, however, because "swinging" a compass, even an electronic fluxgate, is a tricky proposition, and you may find through observation that what you think is a reciprocal course is actually 10 degrees off.

Good luck and I hope this helps.

[Valiente]

Originally Posted by Omatako

I must say though that these things are more sensitive than I thought. My wife put a piece of clothing into a drawer alongside the fluxgate and it had something metal in one of the pockets and the AP was distinctly unruly until we found it.

Too true, Andre. I was standing on deck near the fluxgate sensor tying something to the roof rails, and I put down my rigging knife about a foot from the fluxgate sensor. My wife reported that the thing went a little mental, which makes me glad I didn't have it tied into an autopilot. After I put the knife back on my belt (below the "plane" of the sensor, I guess), the device behaved itself after 10 seconds of mulling it over.