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TOPIC: compass alignment

compass alignment 12 Oct 2021 19:38 #126258

  • Matthew Arnold
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Thanks all. Believe I am defeated by steel. Never mind it is primarily there for Rhine certificate compliance. Might just have to rely on my iPhone when a reading is actually needed

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compass alignment 12 Oct 2021 18:58 #126254

  • David Puttock
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Hi All
We have a second hand ex.trawler compass,its mounted on hard teflon sheet on the steel coachroof, the reason for the teflon sheet is easier to drill and tap than the steel,and no risk of water entering the wheelhouse . The compass is mounted upside down in a tube,and read via a mirror. the compass adjuster reads off the deviation, useing small magnets placed in certain position around the compass,and
then bolts down the magnets.You then gat a deviation card which is kept in line of sight by the compass.The mirror can be adjusted to give the helm a good view of the course set. Best Regards Dave Puttock
The following user(s) said Thank You: Andy Soper

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compass alignment 08 Oct 2021 18:02 #126193

  • Charles Mclaren
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If u mount it permanently and then get a compass adjuster he will correct it professionally with magnets and give you a deviation card which will tell you how far out it is on each point of sailing. But if it’s a cheap compass flog it and get an electronic one. C

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compass alignment 08 Oct 2021 16:38 #126186

  • Balliol Fowden
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Our old Sestrel remote magnetic sender compass works fine with the sender just below the timber wheelhouse roof. It corrects within a few degrees (probably better with patience) and is only really affected by very large local currents, for example when our big electric steering motor on the steering winch under the dash is used (but this is only used when manoeuvering so doesn't matter). An edge reading magnetic compass would probably be adequate in a timber wheelhouse if mounted high. However, if your wheelhouse is all steel (as we now know) then you have little option but to install a fluxgate compass, perhaps up the mast. Two to three metres off the deck should be fine. Or at the top of a long sturdy ensign staff aft? The down side for some would be the digital readout, if you're used to steering to a compass needle / card, and I guess that you need to find a wiring route for the cable that is well clear of other electrical influences through the boat if you have a traditional mast up forward.

I don't think you can "insulate" a standard magnetic compass without insulating the earth's magnetic field as well!

Can you turn the compass you have over, or edge read it? It might be worth trying to hang it under the wheelhouse roof, in which case it might be sufficiently clear of electrically induced fields and correctable, albeit perhaps with a rather errant deviation card, but as a steering compass it might work adequately, backed up by GPS to confirm your track. You don't need a great degree of accuracy: if out of sight of land you will likely be rolling too much to steer a steady course anyway!

There is a school of thought that a fully corrected and accurate compass is not really that vital for what might be basically an inland cruising barge. When I used to deliver a few barges in the 80's & 90's cross channel I used to take great care to swing and correct a compass for every trip, but once GPS became accurate enough I confess that I did quite a few channel crossings using GPS for the main part of the job, with just a good hand held compass to use out on deck or hold up under the wheelhouse roof, just to confirm things occasionally, take bearings or for any emergency. We did always carry several GPS devices though, and prayed that America didn't go to war!

Balliol.

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compass alignment 08 Oct 2021 15:30 #126183

  • Matthew Arnold
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Colin
thank you. I think I may have wasted 60 Euro. My whole wheelhouse is made of steel including the roof. There is no practical mounting point that is >1 metre away from steel..
Matt

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compass alignment 08 Oct 2021 14:42 #126182

  • Colin Stone
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Matthew,
A difficult one.
I guess it doesn't have it's own iron balls to compensate?
I recall that magnetic compasses should be a metre from any magnetic influences.
From my own experience, I fitted a KVH fluxgate compass with a remote sensor which sits in the bilges surrounded by steel.
It works fine and after doing slow calibration circles it is pretty good.
www.kvh.com/admin/products/compasses/compass-systems/azimuth-1000/leisure-azimuth-1000
I also have a Silva 70UN handheld mounted up under a glassfibre roof and 1m from any steel. This has an optional mount with correcting magnets, so is now fairly accurate.
silva.se/product/compasses/marine/compass-70un-2/
It is compensated via the 2 holes visible in the base with a small brass screwdriver.

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Colin Stone
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compass alignment 08 Oct 2021 14:18 #126181

  • Matthew Arnold
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Hello all
I recently bought a new Riviera compass that was supposedly not affected by metal. Turned out not to be the case. It sits on top of the dash that has a whole load of electrical wires underneath which is throwing it off about 90 degrees and basically holds it there regardless of direction. If I hand hold it in the middle the wheelhouse its fine (but hardly practical).
Does anyone know a technique to "isolate/insulate" the compass to get a correct reading.
many thanks
Matt

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