My yacht has twin wheels and two large liquid-filled Plastimo steering compasses, writes Norman Eastwood.

When I bought the boat seven years ago the starboard compass had a tiny bubble of air in it and the port one had a large bubble.

But over the last seven years, both bubbles had increased in size until the dome on the port side was barely half-full.

With no obvious leak, I can only assume the oil inside was finding its way past a seal and evaporating over time.

In any event, a refill was needed so I started with the port compass.

Removing the liquid-filled compass from the pinnacle was just a matter of taking out the four screws holding the plastic shroud that covers the light fitting.

Unless the bulb has failed there’s no need to remove the two small screws, which only give access to a tiny ‘grain of wheat’ bulb.

With the shroud removed the compass was still stuck down with some sort of foam rubber gasket, so it had to be prised carefully from the binnacle mounting.

Once free the liquid-filled compass will still be tethered by the wires to the light fitting.

Do not remove them, but pull up the slack on the cable and invert the compass to stand it upside down on its own mounting so you can work on it.

1. Removing the screws

Credit: Norman Eastwood

I first removed the four small stainless screws that hold the adjustment cap in place, and then the two larger black screws that hold the plastic fitting to which the adjustment cap is attached, but found in fact there’s no need to remove the four small ones, only the two larger black screws.

2. The mounting ring

Credit: Norman Eastwood

The fitting itself is retained by four plastic lugs which need to be sprung inwards with a flat-bladed screwdriver before the fitting can be lifted off.

In this photo, the adjustment cap has been removed separately, but there’s no need to do this.

The white tape was to remind me of the correct orientation of the adjustment cap.

3. The bellows

Credit: Norman Eastwood

This reveals the bellows that allow for expansion and contraction of the oil in varying temperatures.

The bellows is retained by a plastic ring, held by eight screws, so I removed these and took off the bellows to reveal four holes.

I believe that slow leakage must have occurred between the bellows and the bottom face of the compass, as the bellows in both compasses appear undamaged

4. Bellows removed

Credit: Norman Eastwood

I drained and kept the remaining fluid for use to top up the starboard compass.

It was a very thin, colourless, oily liquid that smelled a bit like paraffin.

On pouring it out there also came a few drops of a heavier green oil, but I was careful to save only the colourless fluid.

In the absence of a supply of the correct (and doubtless very expensive) compass oil, I decided to use Johnson’s Baby Oil, which is largely made up of liquid paraffin and isopropyl palmitate: the latter ingredient is made of isopropyl alcohol and palm oil.

As none of the ingredients look at all injurious and it is light-bodied and quite colourless, it seems to be an acceptable choice.

If I were doing this job in the UK I would instead buy pure Liquid Paraffin BP from a pharmacist as the other ingredient in baby oil is an emollient
and thickening agent, which is not needed in the compass.

5. Initial filling

Credit: Norman Eastwood

With the bellows removed the bulk of the oil could be poured in using a small funnel.

I’d initially bought two 500ml bottles of baby oil, which proved not quite enough – the liquid-filled compass actually holds nearly 1,100ml.

6. The filler screw

Credit: Norman Eastwood

To complete the fill it’s necessary to remove a brass filler screw, sealed in place at the time of manufacture by apparently melting plastic over it.

Before breaking the seal by drilling it out, replace the bellows and its clamping ring so that no debris can fall into the compass.

The thin plastic covering and the surrounding material are very brittle, probably as a result of the heat used to make the seal, and great care is needed in drilling to enable the screw to be removed without damaging the compass body.

7. Injecting top-up oil

Credit: Norman Eastwood

An essential tool now is a small syringe – the type that comes with an inkjet printer cartridge refill kit is ideal.

With the compass balanced with the filler hole uppermost I injected oil until some ran out, then replaced the screw and its tiny O-ring seal.

On turning the compass upright there were two issues: firstly, the compass card was now standing on edge, and secondly there was still an inch-wide bubble where the air that had been trapped between the housing and the bellows had surfaced.

8. Successfully filled

Credit: Norman Eatwood

Another inversion and top-up solved that problem, leaving only a tiny bubble.

The compass card came upright after carefully rocking the unit from side to side.

I have not resealed over the filler screws in case any further top-up is needed.

As they seat on O-rings I don’t reckon they’ll leak – they were certainly dry on both compasses when I broke the seals.

The starboard compass just needed minor topping up, so I only removed the two black screws holding the fitting and the adjustment cap, and unsealed and removed the filler screw.

In topping up any compass it is important to ensure that the bellows is neither fully extended nor contracted, but has room to allow for both cooler and hotter conditions. It is quite easy to check this when filling.

Although both compasses had air bubbles of about 4mm in diameter in them immediately after filling, by the following day the bubble in the starboard compass had disappeared completely.

Whatever the original fluid in it is, it seems to have the property of absorbing air. And after three weeks the bubble in the port liquid-filled compass, filled with baby oil, had also vanished.

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