compass for autopilot on a steel boat

Kater · #1 (**permalink**) 02-28-2008

Hi all,

For a while i've been reading about problems and solutions on this forum and now it's finally my turn to be in trouble. A good excuse for a first post!

The situation: I have a 40 ft steel yacht and i have been fitting it for ocean passages the last two years. Our first trip from Holland to Norway last summer was pretty tiring because we had to hand steer her all the way since we didn't have an autopilot yet.
This put the autopilot at the top of the 'to do' list of this year. Now, I've done extensive research and finally decided what kind of pilot I wanted (a Furuno navpilot FAP-500, with a large hydraulic ram directly on the rudder below decks.) This thing needs an electronic compass for a heading input and also to use the gyroscopes as an indication of rolling, pitching and turning which can be directly compensated. Great system I thought, but here's the problem:

Compasses don't work inside steel hulls! I completely overlooked this but a nice dealer pointed it out to me. So the compass has to be above deck, about 1,5 meter away from any steel. So it could be on the mast, but it's pretty big (especially with a watertight cover), and I'm afraid of the jib or anything else hitting it. Or it could be on the stern on a pole or something (which I don't have, but oke).

Now, my question is, how do other steel boats deal with this problem?

Maybe my first post is a bit long, but i hope you have some ideas!
Thanx anyway!

tdw · #2 (**permalink**) 02-28-2008

Can't help you with this despite owning a steel boat. Our auto pilot doesn't use a compass, you dial in the course manually. Maybe you have to go with a more basic system.

Valiente is the other notable steeler here and I'd guess he'd be more up on this kind of thing than I am.

One other thought, do you know of the Metal Boat Society ? I'm not on my main computer so I don't have the link with me but just google it and you'll find them. Someone there is bound to be able to assist.

chucklesR · #3 (**permalink**) 02-28-2008

Compasses not working on steel ships is news to any Navy man (me for instance).
Certainly they do. You add large steel balls (binnacles?) beside them and then tune the compass. A little google goes a long way.

Staying on course - The Boston Globe

The rest of the story:
Steel Boat Compass Problems

Flux gate compass, same deal, you tune them to offset.

billyruffn · #4 (**permalink**) 02-28-2008

Kater,

Don't worry -- you can make it work. I'll post a couple of photos showing the position of two fluxgate (electronic) compasses on my steel boat. The first one is a Raymarine compass that I use for both a ST4000 tiller arm (that drives the Aries on a compass course) and for the Raymarine S3G Corepack (autopilot electronics package for the main autopilot. In the photo it's just over the shoulder of the crew person in the red foulies. It's located on a SS mast on the stbd side at the stern approximiately 5 feet off the deck. It works great.

The other photo (I will put in a separate post below this one) shows the location of the compass for my old autopilot, a Coursemaster 700 or 750. The electronics package of this autopilot went south on me and I replaced it with the Raymarine unit mentioned above, but I've kept the compass as a backup. The compass is to the right and above the shoulder of the guy in the yellow shorts. Its located on the centerline of the boat over the main hatch. The hard dodger the compass is mounted on is fibreglass, but the rest of the boat is steel. The closest steel to this compass is the surface under the right arm of the guy in the black tee shirt. My guess is that this compass is no more than 2 feet from the nearest steel. This compass worked well for 7 years and lots of miles.

Check with the manuals that come with your autopilot -- they will specify how far away from the hull you need to be. My guess is that the Raymarine installation (the compass in the first photo), is probably a better bet.

One thing you need to be aware of is that the modern "smart" autopilots CPUs are as sensitive to magnetic interference as the electronic compasses are. When I replace the Coursemaster with the Raymarine, I put the Raymarine "black box" in the same location the old Coursemaster electronics were located. This was on a bulkhead in an aft cabin, approximately 2 feet from my genset. My logic was that if the Coursemaster worked there, the Raymarine should. It didn't. The magnetic interference from the genset was too great and the Raymarine Smart Pilot was decidedly dumb. When I relocated it away from the engine / genset space, it got 'smart' quickly.

Good luck with your installation. Send me a PM if you need any more help.

billyruffn · #5 (**permalink**) 02-28-2008

Here's the second photo showing the old compass (wrapped in white tape over the left shoulder of the guy in the yellow shorts). The left arm of the guy in black is leaning on steel -- everything in you see in that plane is steel. The hard dodger is fibreglass.

sailingdog · #6 (**permalink**) 02-28-2008

You really need to have a compass that is designed for use on a steel boat. They'll have two large quadrantal correctors, the balls Chuckles is talking about. Might want to PM Steelboat, since he has some experience with steel boats...

Plumper · #7 (**permalink**) 02-28-2008

I skippered a steel boat and the fluxgate was mounted halfway down the companionway. It didn't have correctors like a normal binnacle but it was capable of being corrected electronically. It was a bit tricky to set up (it involved sailing in circles for a significant period of time) but once done it stayed corrected for good.

Those big Navy ships have Gyrocompasses these days. They stopped using magnetic compasses many years ago. I was Captain of a minesweeper that had a binnacle with a magnetic compass and swinging it was a yearly ritual that I didn't look forward to.

Plumper · #8 (**permalink**) 02-28-2008

Quote:

Originally Posted by sailingdog

They'll have two large quadrantal correctors, the balls Chuckles is talking about.

Nelson's balls.

sailingdog · #9 (**permalink**) 02-28-2008

Oops..just re-read the OP...and realized this is for an autopilot...that'd be a fluxgate compass.... and many will work on a boat stock...just have to be calibrated for the boat.

billyruffn · #10 (**permalink**) 02-28-2008

Dog,

re the main compass on a steel boat....

Billy Ruff'n uses a standard Plastimo yacht compass without the steel balls. It' works fine -- I had it swung by a professional in Honolulu when I got a new one (old one caught the French champagne disease ... tiny bubbles) and the deviation was only a couple of degrees on some headings and zero degrees on others. I think it's a different story when the compass is located in a bridge house that's basically a steel box. Our compass installation is identical to those found on fiberglass boats.

The calibration of an electronic compass that Plumper mentions above is a standard procedure for electronic compass calibration. It's done when any new electronic compass is installed (regardless of hull construction) and consist of running the boat in slow circles until the compass figures out what's up.