Compass Storage off-boat?

[Matt J.]

So little Rarus is almost tucked in for the winter, and I removed most of the "removable" items given that the town she's in hasn't got the best reputation (I was told point-blank to not leave anything that could be stolen). Not a really bad town, but has a bad reputation.

Anywho... I took the compass off, and set it in the car. Left it for a coupla days (stupid me). Took it out and it started drifting and spinning uselessly as I walked away from the car. As I brought it into the garage, I realized there were no really good places in there free of ferrous metals. Seemed like every sheld sent it in another direction. I think there's already some error in it, and I need to figure how to correct it (I'm afraid I have to open the famous gronicle thread from years back).

Is there a way of storing the compass that won't further degrade its accuracy? I mean, aside from clearing all the shelves of tools, cans, gizmos and gadgets?

It's a nice 6" compass, which came with the boat, with interior and exterior mounts. I beleive a Constellation?

Thanks.

[cbob]

Mat, When they lay up big steel ships, the compass' stay in place, surrounded by ferrous, never a problem, then swung on reactivation/breakout, sometimes, to confirm compensation within limits. This compensation is to negate magnetic forces created by the steel structure, not that the compass has gone goofy. If you feel your compass is inaccurate, confirm your feelings. Your compass (I have a 50 year old Connie) is fine. What could cause this suspected innacuracy? Anybody? cbob

[Matt J.]

I checked it against a hockey puck compass this summer (which was "certified" before I bought it) and found a difference of approximately 6-7 degrees, minus any optical error.

So the compass being pulled off all winter by nearby objects shouldn't have any lasting effects?

[Andrew Craig-Bennett]

My compass is 66 years old; stored off the boat each winter and indeed stowed below on the mooring, now that I have come to realise that it is an "antique".

Stowing a compass near ferrous metal will have no lasting effect. However, when a compass is approaching half a century or so, a visit to a compass repairer to check the sapphire and needle, card floats, magnets, etc. may not be a bad plan.

[Bruce Hooke]

6-7 degrees of error does not sound exceptional to me. With a high-quality compass a professional compass adjuster could make adjustments to reduce this. Another option is to construct a conversion chart so that you know what adjustment to apply depending on the heading you are on. It's a bit of a painstaking process but such an adjustment table can be constructed by putting the boat on a known heading (e.g., starting from a known location and pointing the boat at another know location, with the bearing between the two points picked up off the chart and then checking what the compass actually reads).

The one time I saw a compass adjusted professionally the guy who did it brought on board a gyroscope to use as a reference. This made it very easy to determine how much the compass was off and then from that first adjust the compass and then if necessary create and adjustment table.

[Mike Field]

.
I agree with Bruce that a 6°-7° error doesn't sound a great deal. And with Andrew that a health-check now would probably be timely.

But you should not expect a compass adjuster to get rid of all compass error for you (although it is a possibility,) and you should expect to have to draw up a deviation table if you want to do accurate compass work.
.

[nedL]

I believe that a compass (by itself) can be stored anywhere (ferrous near by or not) with no problems. You are not going to do any harm to the compass, it just won't be pointing to "N" while in storage. (I wouldn't recomment storing it near a strong magnet though.)
As mentioned, the problems come when the boat is stored (esp. steel boats), the ferrous objects on board take on a magnetic set over time which will effect the compass when put back into service (this is deviation). For this reason large high quality ship yards traditionally had their building ways facing in a north-south orientation, to minimize the inherent deviation in the compass. Any significant welding that is done on a steel ship may significantly & permanently affect the compass deviation.
Oh yes, and you can only "check" or "correct" a compass when it is properly positioned aboard the vessel, in the location it will normally used in. This process is called "boxing the compass" - you can read about that in Bowditch. You can not take a compass to a 'compass repair guy' and have him correct it - 'it just don't work that way' . He can fix an actual problem with the compass, but he can not hand it to you & tell you that it's all set to go and will be accurate when on your boat.

[ 12-10-2003, 08:16 AM: Message edited by: nedL ]

[JimConlin]

It's best not to expose it to freezing temperatures, so bring it home.
If you're unsure about its condition, have it looked at by someine competent. I recommend White Instruments (http://www.robertwhite.com/) in Boston. Their forebears made the Constellation compasses.

[Art Read]

The compass I put aboard the Dark Harbor is one that has been in my family for decades. It's a little "box" compass, (minus the box) that either came with the house in Provincetown, (built in the 1880s) or the old daysailor I grew up with, (built in the 1920s). Either way, it's quite old and had spent probably forty years or so tucked away on various bookshelves, at the bottom of old chests or, as when I found and finally "appropriated" it, buried in a pile of salvaged "knick-knacks" after a bad house fire. (I cleaned the carbon and soot off it myself...)
I then carried it around with me all through college, bachleor apartments and various, dubious "storage" sites during my sea-going years.

When I ran across it again during the "contemplation" stage of my boat-building project, I really didn't expect it would be much use as a true navigational instrument any longer. (It, too, just sort of spun aimlessly every time I picked it up) But it seemed so perfect for the boat that I went ahead anyway and built a little bracket for it on the cockpit coaming. (Besides, it makes for a good support for the boom crutch and it "looked" good there...) Damned if it doesn't seem to work perfectly. As near as I can tell anyway. Since the launch, I've compared it to "working" compasses on boats moored alongside me on several different compass points. If it doesn't match perfectly, it's too small a deviation for me to percieve. And the motion of the boat underway doesn't "upset" it nearly as much as just walking around with it in my hands does. I do still plan to take it in eventually to be professionally restored, just 'cause I think it deserves it, (I'm also hoping the compass restorer can tell me something about the "particulars" on it... maker, true age, etc...) but I'm already really pretty impressed by that little guy! It's been tossed about for years, jumbled up with all manner of "harmful" objects, (a cast iron doorstop for one!) exposed to freezing temperatures repeatedly, and even survived a house fire... I guess maybe the maker assumed these things just might not spend their lives "cossetted" in velvet lined, temperature and humidity controled, jewelry boxes?

Anyway, with regard to your compass, if I were you, I'd wait 'till spring and reinstall it before deciding if further action is needed. My guess is that her previous owners probably didn't treat that compass much differently than you have? Just a thought...

http://www.imagestation.com/picture/sraid70/pc33ecc11ac0d6fa552baa5d66dafa04f/fba1f363.jpg

(And yes... It's pointing North in the picture above. I checked. ;) )

[Dan McCosh]

A compass is always living in the midst of a magnetic field--the Earth's. It will point to any magnetic material, such as steel, without any harm. Only problem would be leaving it in the midst of an actual artificial magnetic field--near a large electric motor running, etc. I wouldn't worry about a steel shed.

[Jack Heinlen]

Stowing a compass near ferrous metal will have no lasting effect. Is this true? I stored a Silva lifeboat/hand bearing compass in its bracket atop a centerboard case containing a steel board, and it developed a twenty degree set. Was that temporary? I put it aside. Should I look at it again?

[ion barnes]

Yup, its temporary, more correctly it is deviation because of its close proximety to the steel. If it were kept anywhere else it would have a different deviation for that spot on your vessel. the deviation can be lessened by swinging the compass by a professonal as had been said before. No worries, honest.

[nedL]

Jack. - Yep the problem was that big hunk of steel (centerboard). There was nothing wrong with the compass. As soon as you moved the compass away from the conterboard it should have been ok.

Years ago we had some guests aboard our family boat for a while & we asked them to help stow some food on board. For the next couple of days we couldn't figure out why the remote reading compass on board didn't agree at all with the direct reading compass. After doing some investigating we found that our guests (in their helping to store the food)had stowed a big can of something right next to the magnetic 'base unit' for the romote reading compass!! Moved the big can & things were fine again.

[Jack Heinlen]

Hey thanks, I'd kinda written it off, or thought I'd have to send it back to Silva to be fixed. I haven't looked at it for a number of years. It wasn't just when near the iron, being stored near it had wonked it when compared to the bearing compass in my Fujinon binocs. So you all think it was temporary, that's good news.

[nedL]

I will say that the magnets in a compass can loose their magnetism which will mess it up. This can happen over time , or by placing it close to something that is strongly magnetic for a while. - Jack, your centerboard didn't get magnetized somehow did it? - Just some more .002. ;)

[Jack Heinlen]

The compass was only atop the case for about a week before I checked it and found it had a set. I had some vague memory that storing a compass near big chunk of iron could be bad for it, and pulled it, and sure enough it was off.

Now, to be honest, maybe it was off before, I'd never had a rigorous look, but given how far out it was I doubt it. And I checked it against a simple hand compass and against the bearing compass in the binocs, both of which agreed it had gone wonky. :confused: smile.gif I'll have to find it and check it again, though the compass in my binocs doesn't work anymore :mad: , but that's another story.

[davef]

Wonder what this means to all of this...

http://observer.guardian.co.uk/international/story/0,6903,837058,00.html

[Hwyl]

Assuming the compass is corrected for deviation and has corrector magnets. I'm sure I read somewhere that you are supposed to take the "corrector" magnets out for storage and put "keepers" on them. It goes without saying that you should mark where they came from.

An amusing story, I once helped deliver a steel boat from Mallorca to Antigua. We didn't have time to check the compass, but assumed it was near to correct. Anyway since our course lay between the islands of Ibiza and Formentera (a narrow channel) we left Mallorca at night expecting to make landfall between Ibiza and Formentera in the dawn light. Dawn saw us north of Ibiza (a 25 mile 25 degree error). Anyway we stopped at Gibraltar and after some wonderful Bass and fish and chips. We started talking about our problem. Another yachtsman offered to help us prepare a deviation table, so we set off next day and had the detailed chart of Gibraltar (lots of landmarks) we all put our heads and protactors together and ended up with a nice smooth graph (with huge deviation). We later found the corrctor magnets stored below, but by that time we were onto sextant nav' with azimuths and etc and were used to the table. Back to the story; when we got back to the marina, a Gibraltar policeman approached us and asked, who was the navigator? "Me" I replied. "You are under arrest" came the response. Apparently (in those days relations between the British and the Spanish were not great and sovereignity of Gib' was being disputed) we had crossed the Gib' /Spain border at least 7 times while pirouetting around the compass, and he was convinced that we were involved in some kind of smuggling.

I managed to persuade him to call the port authority (which was the Royal Navy) and a very amused senior officer came down and persuaded the policeman to release me. Great days