What kind and where do you mount your compass?

Started by Scooter, Jun 23, 2023, 01:36 PM

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Scooter

I just noticed in an unrelated post Charles has his dead center on the companionway which I haven't seen before but makes lots of sense for usability and correctness. My p-19 doesn't have one (or two) yet so I'm looking for ideas. What's worked, maybe what hasn't?

Charles Brennan

#1
Scooter, My compass was mounted there to deal with two problems:
1) A 400 pound cast iron swing keel that did not cause much magnetic deviation when down, but was a major problem when retracted.  You could actually crank the keel up and watch the compass move.
2) Relocating a battery forward for weight distribution reasons, caused wiring to have to be run down the port side.  The wiring was large to deal with voltage drop issues and difficult to twist sufficiently, to cancel out stray electromagnetic fields. Turn on all the nav and cabin lights at once and the compass would "jump" to the magnetic deviation and settle back closer to "true", when all the lights were switched back off.
Both of those problems ruled out a bulkhead compass mount.

The only place unaffected (or least affected) by those two problems, was on top of the companionway hatch.
The compass bracket performs two functions:
1) Holds the compass.
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2) Holds a companionway cover when at anchor or beached.
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Bear in mind, that when I first was doing all this, it was before GPS and cell phone positioning at your fingertips. 
I had a compass deviation card and the whole bit.
I originally set it up in Biscayne Bay, by going out to a shoal and sighting the boat between channel markers whose bearings I had figured out on the charts. Because of the compass center mounting, I was able to use the hull as a "lubber line" standing at the stern and sighting across the transom, to the compass and then to the mast, as a lubber line reference.
I literally "swung" my compass by swinging the entire boat!
The shoal was long and skinny, and I had set my reference bearings to the channel markers by using both ends of the shoal to cross-check my bearings to the channel markers.
I then set the compass N-S deviation adjustments and E-W deviation adjustments as best I could, then plotted the rest of the deviations on the compass deviation card.

The compass has 45ยบ "tacking" lines and is convenient for steering from either side of the cockpit.

To answer your original two queries:
1) What kind?
The biggest one you can comfortably use and place aboard your boat.
With smaller compasses, what looks like a minor deflection might be 15 or 20 degrees of course variation.

2) Where?
As far from metal as you can get it, in any direction.
Besides my electrical wiring in front of the compass, the keel forward and under the compass, I also have to deal with a block of metal behind the compass in the form of an outboard motor.
And occasionally, I have a Bluetooth speaker hanging from a Bimini top, strategically positioned away from the compass. Basically think metal, wiring, and electronics, such as speakers, outboard chargers when the engine's running, etc.
Try turning all this stuff on one at a time and then all at once and observe your compass.
There's nothing real subtle about it, for the most part it won't swing slowly around, it will "jump" when a sudden electromagnetic current is introduced near it.
Don't be discouraged by all the opportunities for deviation aboard your boat.
One thing working for you, is that magnetic interference is subject to Gauss (G) forces, which are exponential in nature.
Double the distance and you now have the square root of the original force, for example.
That's why my compass is still very useful even being surrounded on all sides by magnetic interference.

Hope this helps,
Charles Brennan

Norm L.

Position will depend on cockpit layout and the type compass. Of course it is most desirable to have it where you can read it from your usual conning spots and also away from metallic or electrical influences.

Many are mounted on the aft face of the cabin as a gimbled design or in the aft face as I had the compass that could be read from the cockpit and cabin.
Here it is on the N24.You cannot view this attachment.

pgandw

Quote from: Scooter on Jun 23, 2023, 01:36 PMI just noticed in an unrelated post Charles has his dead center on the companionway which I haven't seen before but makes lots of sense for usability and correctness. My p-19 doesn't have one (or two) yet so I'm looking for ideas. What's worked, maybe what hasn't?
Had a nice compass on my ODay 25 before GPS.  Worked fine, used for crossing the Gulf Stream to the Bahamas and back.  EXCEPT when a guest with a pocket knife in his pocket sat near the compass, and threw it off 30 degrees.  Didn't discover what was going on until 3 hours later when my RDF positions were way out of line with my intended compass course.  Then guest got up and I saw the compass suddenly swing 30 deg.

Currently, my Mariner (19ft) doesn't have a compass.  So far, only day sailing, haven't had to do any navigation except by eye.  Looking at a 3 day August cruise in Long Island Sound, I need to experiment with the Navionics Boating app I have on my cell phone.  This gives me charts.  I should be able to lay out a course and GPS track over ground.  Previous owner just used a GPS compass.  I'm really not anxious to install a compass but will probably do so eventually.

Going to make do with a portable, battery powered anchor light on the jib halyard and forestay for anchoring overnight - boat has no electrical system but running lights were factory installed (no wiring or bulbs!).

Fred W
Stuart Mariner #4133  Sweet P
Yeopim Creek, Albemarle Sound, NC

Spot

Cockpit, starboard side of companionway bulkhead.

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Big dreams, small boats...

Travis Chapman

#5
I tried the Charles method on my Windrose 18 for a season and busted the bracket. Also tried a version attached to the companionway hatch lower board. In the end, I went with the version in this video. Same warnings as others; it's a small boat, so everything is trying to mess with your deviation. I use mine for course tracking, not so much for navigation.
=============
SV Panda Paws
Windrose 18
Glyndon, MD

Charles Brennan

Travis, GEEZE!!! DUDE!!!
And I thought *I* was a gadget nut!!  :o

I DO have an inverter aboard Urchin, but it only has 2 outlets, not TEN!!!
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I used to work in the electronics industry and have my fair share of gadgets, but nothing like THIS!! :D
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I bow to the Master!! :D

Charles Brennan

noelH

Just a plastimo handheld bearing compass that sit in a bracket mounted to a board that slides into the companionway.  Easy to read from any position in the cockpit.  Slides off the bracket and becomes a handheld bearing compass. 

Spot

Quote from: noelH on Jun 24, 2023, 05:03 PMJust a plastimo handheld bearing compass that sit in a bracket mounted to a board that slides into the companionway.  Easy to read from any position in the cockpit.  Slides off the bracket and becomes a handheld bearing compass. 

Nothing wrong with simple and versatile.

I also have a set of binoculars that has a compass and a nightlight for reading the compass.
Big dreams, small boats...

Scooter

I'm all about simple and versatile, and I don't plan on going farther than I can see for a while but I don't think I'd be comfortable relying only on a hand bearing compass.

Cockpit, starboard side of companionway bulkhead is the default spot but that's also where I like to rest my head sometimes and there's not a lot of space for both.

I like the companionway hatch mount but I don't think there's enough meat there for me to make that work.

noelH

Started collecting sailing hardware a few years before I ever owned a sailboat.  Also, bit of a compass and binocular junkie.  Still own and use my 80's vintage Silva.  Picked up the Plastismo Iris 50 (hockey puck style hand bearing compass) a while back.  It was going to be my boat compass.  My addiction led to purchasing the Iris 100 and mount.  The 50 sits in the "go" bag as a back up.  Pre-recession scored a good price on the Steiner Marine.  Nice 50mm optics with the built in compass and mass to keep a steady view.  It's what I use more often as a bearing compass.  Only bummer was not removing the battery or replacing it before it leaked. No more night time illumination.

I embarrass myself with my poor dead reckoning "skills".  On the light wind days nearshore sailing there is plenty of opportunity to verify your position. I would be GPS dependent in open waters with nothing to take a hand bearings with.  My estimation of speed, distance, drift really stinks.

Travis Chapman

I may have 2 outlets off the inverter, just for a small laptop and Ryobi battery charging in an emergency; that gang is all 'shore power' only 😇 I'm always looking to try to make something work, what can I say?

I've always appreciated the handheld models that can fit in brackets. I'll bet you can fabricate a nice one in wood or 3D printing if you happen upon one 2nd hand without the OEM bracket too.
=============
SV Panda Paws
Windrose 18
Glyndon, MD

Frank B.

What kind?, Plastimo mini contest. Where? starboard side bulkhead.  Truthfully, I haven't had the cover off in years.  I sail a lake know where every thing is,do visual.  At night use the chart plotter if the visibility is bad, compass is backup.  Guess I should check to see if it still works.

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Spot

Big dreams, small boats...

Scooter

That's clean, functional and gorgeous but exactly where I'd like to laze on a long reach.