Compass bubble ?

[Mark.Wilme]

Just how much of a bubble (if any) should there be in a marine compass ? I thought I read somewhere that they are filled with mineral oil that is prone to yellowing with age it left exposed to sunlight (fungal growth or something), if you can buy the mineral oil are they a "refill yourself" job ?

I am asuming that the compassin question is well swung, properly calibrated and in all other aspects in good condition.

Anyone any insight ?

[bcooke]

"Compass fluid" is what is on the can but I am pretty sure it is just clean kerosene. I would get it through aviation supply sources. I am not sure where else to look for it.

When refilling a compass, a small bubble can be tricky to get out of there. Little or no bubble is best as it can affect the movement of the card. Check to see if there is a cap somewhere for filling.

-Britton

[Tim]

I am asuming that the compassin question is well swung, properly calibrated and in all other aspects in good condition.

I certainly wouldn't assume that. Most compasses have never been swung or corrected. If there's not a calibration card on board, then assume that the compass is NOT swung.

I am never sure what is actually inside the compass. I continually hear "mineral oil" or "mineral spirits" and now kerosene. Which is it, actually? There's a big difference between mineral oil and mineral spirits (paint thinner), obviously, so it would be good to know which it actually is. I've never added fluid to a compass in my life, so I don't know.

There shouldn't be any bubble, technically, but many compasses have up to a 1" wide bubble at the top. This doesn't affect the actual magnetic operation of the compass at all; the only purpose of the fluid is to dampen motion of the card. But it's best to have no bubble, of course.

[bcooke]

My textbooks are buried. I tried but I am not THAT motivated...

The somewhat sketchy info on the internet turned up loads of suppliers for 'compass fluid'.

I found a source that said early compasses were filled with alcohol or a mixture of alcohol and water (hence the term 'whiskey compass'). Another source said kerosene used to be common. 'Mineral oil' and 'kerosene' might be the same thing for all I know.

I suspect 'compass fluid' whatever it is, is a more refined and better product and since it seems to be available everywhere would definitely be my choice.

A ran into several pages on the internet discussing the repair of compasses in my five minute search. Apparently some people consider it a hobby.

-Britton

[Tim]

'Mineral oil' and 'kerosene' might be the same thing for all I know.

Definitely not. Mineral oil is a food-safe product that is frequently used to treat cutting boards and salad bowls, and the like.

I have a bottle here that I used to finish the stovetop cutting board on Glissando. The label reads "Intestinal Lubricant" (gross), and the ingredients are "Mixed Tocopherol", which is vitamin E.

It's crystal clear and perhaps a little less viscous than light vegetable oil.

[bhartley]

It just so happens that my husband has worked for three compass manufacturers -- and we have one of the world's leading authorities on compass technology due here for dinner shortly.

Most compasses use highly refined mineral oil which is slightly more viscous than water. The dampening effect comes from the physics of the unit, card, fluid interaction. Ultra-pure oil is used to keep stuff from growing in it. Some compasses he built used very clear kerosene called Isopar.

The bubble shouldn't be there. All compasses are designed to handle extremes in temperature via a diaphram, bladder or other. The compass has to handle the expansion of fluid and this is the primary source of failure.

Anything you want to know about compasses is (sadly) at my disposal! Hope this helps someone out.

Bly

[dasein668]

The label reads "Intestinal Lubricant"

I did not need that, thank you very much.

[Tim]

It just so happens that my husband has worked for three compass manufacturers -- and we have one of the world's leading authorities on compass technology due here for dinner shortly.

Most compasses use highly refined mineral oil which is slightly more viscous than water. The dampening effect comes from the physics of the unit, card, fluid interaction. Ultra-pure oil is used to keep stuff from growing in it. Some compasses he built used very clear kerosene called Isopar.

The bubble shouldn't be there. All compasses are designed to handle extremes in temperature via a diaphram, bladder or other. The compass has to handle the expansion of fluid and this is the primary source of failure.

Anything you want to know about compasses is (sadly) at my disposal! Hope this helps someone out.

Bly

Excellent! Some information from someone who ought to know.

Thanks for the info.

[AJ]

This turned out to be a very timely thread for me. I arrived at the boat the other to find that the old Sestrel Compass mounted on the cabin bulkhead had sprung a leak. At first I couldn't figure out where water was leaking in since I have the whole boat shrinkwrapped. Then when I tried to mop up the puddle with some paper towel I realized that it was actually an oil, not water, and that led me to the compass.

Hopefully, I'll be able to pinpoint the source of the leak and refill it without too much difficulty.

AJ

[Mark.Wilme]

bhartley

Maybe you can help. I have the compass at home upside down on the bench. The fluid is mineral oil and I have a quart of Ritchie oil to replenish it with.

I have tried pumping in new oil with a syringe but even when I think that the fill hole is at the very top I still get a bubble. Do I need to be doing something with the bladder when I do this or is it not a DIY repair ?

Thanks, Mark

[JetStream]

You just have to turn the compass until the bubble is where the fill hole is.

Many years ago I had a compass with a big bubble. Someone told me to fill it with alcohol, so I did. I was anxious to have it right before I left on a trip from Narragansett Bay to Provincetown. It turns out that the compass was actually filled with mineral oil. I was sailing across Cape Cod Bay, at night with no electronics. (This was 1971 and few had electronics.) All of a sudden, all of the markings on the compass card floated off into the fluid and we had no idea which direction was which. With changing wind, no night sky visibility, no backup compass, we spent a night walking around the boat while we were aground on Billingsgate Shoal.

Moral of the story: Only the compass manufacturer can tell you exactly what they put into their compass. The only other safe way would be to have the fluid analyzed.

[Mark.Wilme]

That's some story.

I know that the compass has mineral oil in it because the manufacturer told me. I have figured that if I invert the compass and then level it (actually out of level it) until the fill hole is at the highest point I can use a syringe to pump the mineral oil in and it will displace the air. If I push a little too much in, the bladder expands, I wait for the air to move to the highest point and then I slowly withdraw the syringe. My bubble is a fraction of what it was and each time I do it, it gets smaller.

Beats $200 for a proffessional to do it or not much more for a new compass.

[Tim]

...All of a sudden, all of the markings on the compass card floated off into the fluid...

Ha! That must have been quite a surprise! What a great story.

[Noah]

When it get's cold out you can start to see bubbles that will go away when the fluid heats up. One trick to refilling a compas is to put it in the freezer for a bit before you fill it up. You can also use cold fluid. Then when it get's warm there won't be any bubble at all.