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Bubble in your Compass fluid  

March 20, 2016. An innocent question asked of Alan Mountford, Blue Gum, Falcon 24, and we are starting on another item for our Technical Section.

This is how we got started - an excerpt from Alan in his March 18, 2016 update on Blue Gum's page

The Silva grid compass developed a leak last year as well as having the balance weight drop off the needle.. On pulling the compass bowl out of the gimbals found that the rubberised plastic diaphragm that allows the expansion/contraction of the fluid had split. In fact it had gone completely rotten. I started looking for another grid compass – but alas no one makes them any more. What to do?? I am not at all a fan of conventional compasses. Grid compasses are so much easier to steer a course with and I don't understand why they are not more popular. Anyone who has used one swears by them!

I did a search on EBay and found a second hand Saura grid compass in USA – but then realised it would be balanced for the northern hemisphere – so no good here.Then I was notified of a Sestrel grid compass in Victoria, Australia. The seller told me it was 30 years old but had sat on a shelf in his garage and not been used. He was wanting A$450.00 for it. It looked as good as new from photos so I put in a bid for it and was successful.

On arrival found that in transport one of the grid lines had come detached from inside it and was floating around free. Obviously the glue holding it in place had deteriorated with age. I contacted a compass repairer to see what it might cost to repair and his reply was it would be uneconomical to do so and the seller wasn't willing to pay repair costs. So had to send it back and get a refund.

Then I looked at seeing if there was any way to repair the existing Silva compass since they are a sealed unit held together with a swaged brass band. As I am an engineer and have a lathe was able to carefully machine off the brass band and get it apart. I then got a piece of brass bar and machined it up and then soldered on a corrugated copper shim to the bottom for a diaphragm. I glued on a new balance weight to the needle then epoxy glued the brass base in place. Took a few goes to remove all the bubbles when I refilled it – but seems OK now - and no leaks.

My compass on Marionette has a small bubble in the fluid on top - a replacement is about $250 new. Click on photo at right for a larger image. I wonder what Alan would do?

Alan's reply

Is there a screw plug in your compass where you could add fluid? You'd need to know what the fluid is to top up with the same type.

The manufacturer should be able to help you there.Some use alcohol or an alcohol/water mix, some use white spirit, some use parrafin oil (lamp oil) etc.

I used a blunt end hypodermic needle and syringe to put the fluid in. I used lamp oil – also called refined kerosene I understand



Another approach - make yourself a nice drink, type 'air bubble in my compass fluid' in your browser, and read....






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