The case of the disappearing diesel

When we left New Caledonia on our way to Australia some 15 months ago, we did the usual and filled up with diesel.

We managed to sail the first day and a half but then there was a cyclone heading towards Fiji which sucked all the winds out of the area leaving us on a glass pond.  And so we switched on the iron genny only to discover that we'd shipped most of our newly acquired diesel overboard.  It had somehow leaked into the bilge and our automatic bilge pump did what it's designed to do, pumped any excess fluids out.  Not good for us and certainly not good for the environment.

Initial investigations didn't determine exactly what the problem was but here we were, miles away from anywhere with absolutely no wind and very little diesel to compensate.  No wonder it took us twelve days to get to Brisbane instead of the anticipated five days: the no wind situation continued the entire trip.

Once we were settled at anchor in Brisbane, Paul set about trying to find the problem.  Nothing obvious.  He tested this that and the other thing and thought that it may be a leaking pipe so adjusted, renewed, tightened etc everything he could find.  Well, time marched on and there was no longer any sign of a leak but Calypso stayed put up the river the entire time so it really wasn't much of a test.

Time to leave.  We filled up with diesel again, all looked OK and set off down the river.  This time, however, we got smart and switched off the automatic bilge pump and, thank goodness, as several hours later, the bilge was full of diesel.  Fortunately, Paul had rigged up a neat system for polishing the fuel (an ideal way of overcoming dirty diesel so often found in the islands) and was able to recover it all, but now to find the leak.  

I was convinced it was in the piping somewhere but Paul was convinced it was in the main tank itself.  When we got to the Whitsundays, he started to investigate how to remove the tank to have it tested.  Well, someone many years ago, took a stainless steel tank and built a boat around it!  There appeared to be no way to remove it without dismantling the boat or, at least, doing a fair amount of damage to the woodwork.  We had to give up on the idea and isolate it until we had more time to tackle it.

As I was so convinced it wasn't the tank, we decided to do some tests.  We filled it with sea water and left it for 24 hours - no leak.  We blew air into it as much as we could manage and left it 24 hours - there was still pressure when we opened it up again.  Haha, says me, it's got to be the piping!   So Paul redid the whole lot again but it still didn't stop the leak.  Damn!  We again had to just leave it isolated from the rest of the system.

Well, here we are in Thailand so many months later and we couldn't put the job off any longer, it had to be the tank and it had to be fixed before we cross the Indian Ocean.  Paul spent two days at it, did two little unobtrusive cuts into the woodwork and, lo and behold, got it out!   And thankfully, Calypso doesn't look any worse for it.  We took it to an engineering shop in Phuket Town who pressure tested it properly and, yes, they found a tiny split in one of the seams.  Oops, I guess Paul was right!  That's now been welded and Paul's busy trying to put everything back together.  He filled it with diesel last night and is happy, no make that thrilled to report, no leak!

Now I ask, how is it possible to leak neither a single drop of seawater nor a molecule of air but the moment it was filled with diesel, it poured out?  It just didn't seem possible but I'm told it's something to do with the viscosity of the fuel.  And so, long may it last as that's a job we don't need to repeat.