# compass for autopilot on a steel boat



## Kater (Nov 6, 2007)

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!


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## tdw (Oct 2, 2006)

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.


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## chucklesR (Sep 17, 2007)

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.


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## billyruffn (Sep 21, 2004)

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.


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## billyruffn (Sep 21, 2004)

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.


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## sailingdog (Mar 19, 2006)

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...


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## Plumper (Nov 21, 2007)

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.


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## Plumper (Nov 21, 2007)

sailingdog said:


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


Nelson's balls.


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## sailingdog (Mar 19, 2006)

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.


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## billyruffn (Sep 21, 2004)

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.


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## Kater (Nov 6, 2007)

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.


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## Omatako (Sep 14, 2003)

*Watch out for soft metals*

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


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## sailingdog (Mar 19, 2006)

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.


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## peikenberry (Apr 26, 2000)

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


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## Plumper (Nov 21, 2007)

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.


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## sailingdog (Mar 19, 2006)

Rigging knife probably... 


Plumper said:


> 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.


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## Boasun (Feb 10, 2007)

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.


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## Valiente (Jun 16, 2006)

Kater said:


> 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.
> 
> ...


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.


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## Valiente (Jun 16, 2006)

Omatako said:


> 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.


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