Saturday, 20 June 2015

Hunting the Leak, or The Curse of the Aluminium Boat

I guess boats and leaks have been inseparable partners since the first person pushed off from the shore on their lash up of sticks and hairy mammoth hide, or whatever.

We've been on the trail of our leak for the last 9 months off and on, with all the frustration that this implies. Our leak however is not your usual drip when it rains or the regular pumping out that many of our classic boat friends curiously take for granted. No, our leak is altogether more serious.

Those of you who know about aluminium boats will know that they're great. Well, they're great as long as you don't drop any copper coins down the bilge, and as long as there isn't any stray electricity floating about.

For those of you who can't remember their school chemistry lessons, I'm not about to give you a revision session, but suffice to say that dissimilar metals blah blah, electrolytic action blah, galvanic corrosion blah, equals a potential hole in your precious aluminium boat in short order.

Most aluminium boats, Sula included, are fitted with an electrical leakage detector of some kind. This measures any current escaping from the boat's wiring system into the hull. Ours takes the form of a push button and two green lights (I can explain the circuit if anyone is interested). When you press the button, the two lights should stay on and equally bright. Any dimming of one and brightening of the other indicates a leak. We press the button several times a day, depending how twitchy we're feeling at any given time.
Anyway, during the latter part of last summer, we began to have discussions along the lines of “do you think that green is a little dimmer?” and “well if you look at it from this angle, or stare at it for a little while.....” etcetera, but that all stopped when we were just south of Copenhagen when one of the lights went out altogether. This was just as we were about to leave Sula to catch a flight back to Devon for a wedding. A hasty disconnection of the battery banks, while not solving the problem, at least prevented any damage while we were away.

On our return a few days later I isolated all kinds of equipment and at some point the problem spontaneously disappeared. I reconnected everything and still no leak. Hmmm. I decided that continuing to look for something which apparently wasn't actually there might not be a good use of time so we shelved it and carried on south towards the Kiel canal.... where it happened again. I started to investigate again but with more or less the same results. I can't tell you how unsettling it is to feel that your precious boat/home/survival capsule is slowly, or not so slowly dissolving beneath you.

So when it disappeared, we carried on. Although through this time, in between the decisive leaks, the slight dimming seemed to be getting a little more consistently worse. It continued to do so until we had transited Kiel, and sailed down the German Bight to Delfzijl, where we entered the Dutch canal system and the problem mysteriously disappeared. The crew asserted confidently that this was because we were now in fresh water rather than salt, which I gently pooh-poohed at the time but subsequently had to sheepishly admit was right, as it returned immediately that we left fresh water the following spring. But in the meantime we did have another full light out episode, which I finally traced to a fault in the anchor winch.

The residual problem remained stubbornly with us. I was unable to tackle it through the winter, as we were in fresh water the whole time, and when we crossed to the UK in the spring, we locked into the Exeter canal.... fresh water again. Only on sailing down to Plymouth could we see that the problem was really back and appeared to be getting worse still.

I called a marine engineer recommended by a friend who then came to have a look. This was really the stimulus I had needed, as I was so underwhelmed by his initial approach that I decided it was time to get out my multimeter, screw on my Mr Determined and Methodical head and seriously set to it.

Three days of work and many hours later, most of which was spent with my head in the electrics cupboard (a small awkward space behind the stove), and the culprit was located. The log, which measures how fast we're going, has a sea water temperature sensor built into it. This had corroded or burnt out and was providing an electrical pathway back to the hull.

After putting back together all the bits of Sula that we'd peeled apart in the hunt for the lost electrons, we felt that a weight had been lifted off us. We now press the button almost every time we walk past it, just for the sense of well-being that the steady even glow of both lights gives us each time.

As we are just on the point of departure to who knows what distant parts, we didn't feel that we could sensibly leave before sorting the problem conclusively. Now we have no more excuses not to really set off south.

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