Fitting a new Compass on a steel boat

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patria

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We have just purchased a 37 foot steel yacht (Cumulant 37 based on a Van De Stadt design) and it requires a new compass (according to the surveyor), as the current one which is mounted on the binnacle in the cockpit has a bubble in it (even though it "seems" OK - we have not sailed more than 20 miles yet). Having never fitted one before, and certainly not on a steel boat, we are getting indications that it is a particularly difficult job to swing the compass after installation. Whats involved and is it a DIY or an "expert" job ?? Are Plastimo difficult or what type would people recommend.



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I think that the problems of fitting a magnetic compass on a steel yacht are generally overstated. My experience is that if the compass is mounted on a steering pedestal towards the aft end of the cockpit then there is no difference as compared to any other construction vessel. Soft iron correctors (or magnets other than as standard fitted to most compasses) should not be required and the deviation low and easily corrected.

If the compass is mounted on the aft of the cabin trunk or on or close to a steel bulkhead, then one is inviting difficulties due to the close and imbalance of steel around it and you may then need professional help.

I have found that compasses actually work surprisingly (but not necessarily very) well, even down below on a steel vessel as long as they are not too close to the steel hull.

If your existing compass works where it is, another will too.

John

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Don't believe everything a surveyor tells you! Depending on the make of compass, it may be cheaper to have the existing compass overhauled - try S.I.R.S for compass repairs/overhauls - Tel; No 01322 383672. If a Plastimo compass, I believe they have their own repairers.

<hr width=100% size=1>dickh
I'd rather be sailing... :-) /forums/images/icons/smile.gif<P ID="edit"><FONT SIZE=-1>Edited by dickh on 21/05/2004 08:28 (server time).</FONT></P>
 
I haven't tried swinging a std. compass (a raymarine fluxgate is fitted, that supposedly sorts itself out) on our steel boat....but a handbearing compass shifts by 20deg+ if I move from the aft deck to the pontoon some 3m forward of the bow, while aiming at the same nearby transit; & alters greatly moving from aft to the wheelhouse.

Having said that, why not try? the basic procedure doesn't seem overly difficult & at worst you get deviation rather greater than you'd like but can call in the experts later if needed.




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I don't agree with MainlySteam on this, achieving good compass accuracy on a steel yacht can be tricky. My new compass had a deviation of up to 40 degrees when first fitted before correction, which is indicative of the amount of adjustment that may be required. And like Andyball, I find a handbearing compass useless.

Correcting is a possible DIY job, the method has been outlined on these forums several times in the past, or guides can be found on the internet. But if you are uncertain, engaging a compass adjuster first time has its merits. It isn't clear why your surveyor has condemned your existing compass. Bubbles can normally be refilled, but might be indicative of a failed expansion bellows. An older compass probably needs new adjusting magnets, and maybe a supplementary, without these it may be impossible to achieve correction. (SIRS will supply new liquid and needle magnets). But your surveyor would have known all this, so possibly there is some other fault.

A steel yacht can change its magnetic field, even by being stored ashore in one position for too long, so you must check the compass periodically, at least every year, and draw up a new deviation curve.
 
In my Van de Stadt 36 CC steel yacht I had the compass adjuster in to fit a brand new Suunto,designed for steel yachts.. I watched carefully as I had to check the compass as I moved around OZ... I dont think it was all that hard,after all if I can do it anyone can .
One interesting point is that he totally disregarded the two " black balls" saying they were useless and only there to make the unit look good... I believed him.
Now boatless , but still mess around and help other steel yyachties adjust theirs...
BrianJ

<hr width=100% size=1>BrianJ
 
At the binnacle. This is a centre cockpit yacht with a diminuitive, deep 'blue-water' cockpit, so fairly close to steel all around. We do have a supplementary fluxgate compass mounted on the mast with a cockpit repeater, which is one way around the problem, but personally I prefer to steer by the binnacle compass, which is now very accurate (or at least it was in January when I last adjusted it). Incidentally, the trickiest part of correction was eliminating heeling error.
 
Must be your magnetic personality upsetting your boat's magnetic field /forums/images/icons/smile.gif - I have seen compasses fitted with no problems adjusting them on pedestals in cockpits of steel boats as small as under 30 foot.

Compasses placed on edge of steel cabin top or with steel dodger or other heavy steel close forward or aft can obviously pose problems (seen one with just one soft iron corrector in these circumsances which is a bit puzzling). Although I know of one small steel yacht with a bulkhead mounted compass and the owner has never mentioned any difficulty with it.

On my own steel boat the compass had only a small amount of deviation when put on the pedestal and was corrected in about 5 minutes. It has not changed in 8 years and is within its reading accuracy in agreement with the fluxgate (mast mounted) on all points and I hence have never bothered with a table of deviations. Maybe the fact that the hull was built very quickly may have had something to do with that.

John

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