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  #1  
Old 05-21-2007
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Lightbulb Refilling Marine Compass

One of the 2 mounted compasses on our boat has lost most of its liquid damping over the years and, before having to replace the unit, we thought we might have a go at refilling it. I understand that the best liquid is a mix of alcohol (methylated spirit) and water. Does anyone know the correct proportions to mix or have any other advice on this please ?

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Old 05-21-2007
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xort has a spectacular aura about xort has a spectacular aura about xort has a spectacular aura about
Contact the manufacturer, Ritchie uses something else, I think it was mineral spirits, but I'm not sure.
If it's an expensive compass, it might be worth sending it off for repair. Mine was a cheap one and I replaced it after refilling didn't work.
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Old 05-21-2007
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Quote:
Originally Posted by xort
Contact the manufacturer, Ritchie uses something else, I think it was mineral spirits, but I'm not sure.
If it's an expensive compass, it might be worth sending it off for repair. Mine was a cheap one and I replaced it after refilling didn't work.
Do what XORT said; as some are filled with mineral oil or machine oil others use pure alcohol, call the company.
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Thanks xort and Simon. I've discovered that the old liquid is actually barbecue lighter liquid. Compass disintegrated on dismantling it so it looks like we have to buy another now anyway. Trouble is getting the right size to fill the hole left by its predecessor !!
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Old 05-21-2007
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The West Marine catalog shows several different compasses, surely one might fit. West Marine - Make Boating Better with New Boating Gear from West Marine
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Thanks. Hopefully I can a suitable replacement nearer to home (Ireland).
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I know this is an old thread but it seems like as good a place as any to add what I have learned on the subject to the collective knowledge base.

Compass Oil

A hundred years ago, alcohol was a common compass dampening fluid but modern compasses use either Odorless Mineral Sprits or an Exxon Mobil product called Isopar L. The difference between the two is that the flash point is lower in the Isopar L product and that is apparently safer in a fire. I don't know about you, but the compass is the last of my worries in a fire. My compass is about 25 years old and so I added Odorless Mineral Spirits from Home Depot with good success. Watch out for the "green" mineral spirits; it is milky white - probably not what you want.

Dissolved Air

The manufacturer and compass shops will tell you that you must put the mineral spirits in a pot and pull a 28"Hg vacuum on it for 15 minutes to remove dissolved air. If you don't do so, you will get a bubble on cold mornings. If you have a paint pot I suppose you could use it together with the manifold vacuum from an idling car engine for this purpose, but there is another way. After you fill your compass with Odorless Mineral Spirits (being careful to leave no bubble), put it in the freezer overnight. In the morning you will find a bubble. That bubble is the dissolved air that the vacuum pump would have removed. If you remove that air bubble, you are good to go. I can think of two ways to get rid of the air bubble. Either apply light pressure to the bellows to force the bubble out or add more mineral spirits.

Some Shrinkage Will Occur

If you remove the plug to add more mineral spirits, you will find that a lot more air is sucked into the compass as the volume of mineral spirits has shrunk due to the change in temperature. No problem, just top it up. Now this is important - as the compass begins to warm up the mineral spirits will expand and you will need to allow the excess spirits to bleed out through the plug (remember, you added alot more mineral spirits that the volume of the bubble to compensate for the shrinkage). Once the compass is close to room temperature you can close the plug and go sailing.

Another Method

I'm sure you're thinking: why not just put the mineral spirits in the freezer overnight. Good question. I used an epoxy syringe to fill the compass and it was all that syringe could do to suck up the spirits at room temperature. The rubber plunger seal kept coming off the plunger. I don't think it would handle the colder temperatures and greater viscosity very well. If you decide to cool the spirits in the freezer, consider that the can will deform badly as the spirits shrink. Leaving the cap loose would solve that problem but consider that the vapors are flammable and a freezer fire might melt your ice cream. I think it's just a tad better to add the spirits to the compass at room temperature.

Last edited by dcmeigs; 06-18-2010 at 11:16 AM.
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Old 06-19-2010
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Thanks, interesting. My compass was in FL for 40 years. After her first winter in NY, I have a bubble. You've given me some ideas.
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Old 07-28-2011
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I appreciate the ideas

I have that same annoying bubble floating at the glass dome of my compass, distorting the magnetic reading.
Thanks for the info on the liquids used and the possibility of doing it myself.
I don't know if I totally agree or perhaps I'm ignorant of the physics/chemistry involved here.
You mentioned, after filling the compass you place it in the freezer and a bubble should reform as the air dissolved in the liquid is forced out. Usually gases are more soluble at lower temperatures, ie warm a bottle of carbonated coke before opening and you'll have a virtual volcano. Perhaps that's not true for the liquid in question??
On the other hand, the new air bubble might be caused by the contraction of the liquid during cooling, resulting in the appearance of the bubble.
Actually come to think of it you may be right, the vacuum pulling out dissolved air and liquid vapor.
So there you go, thanks. I'll give it a shot.
Paul
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Old 07-28-2011
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I just went through this recently. I called a compass repair guy and he told me to fill the compass up and then place the compass in the fridge for the night and in the morning refill it to the top and place the screw in it. This worked great for me. Hope it helps
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