I think — or perhaps I hope — I've solved a serious problem. I have a theory about diesel fuel in the bilge.
Last winter, a hose clamp for the deck drains failed. The winter rains and snowmelt poured into the engine room, and the deep bilge. It froze. The pump broke. The bilge filled to a remarkably high level.
See The Drain Hose for some background. We have diesel in the bilge and on top of the center fuel tank.
I pumped the bilge dry, carrying bucket after bucket to the bilge-water recycling barrel.
Then it was summer and time to go sailing. Most times we got back there would be diesel in the bilge. I'd shut off the pump, manually pump out the bilge, and carry bucket after bucket to the bilge-water recycling barrel.
Tedious, messy stuff.
I think I must have pumped at least 30 gallons of bilge water contaminated with diesel. Possibly more.
My theory is the drain hose filled the center tank, and the diesel is floating on top of the water, and leaking out around the cover plate the same way rain water is leaking in. Indeed, there's an exchange: each gallon of water leaking in displaces a gallon of diesel to leak out.
You can see the red-died fuel in the middle of this picture, with the vent hose sticking out of it.
This weekend, I finally had time to take it very seriously.
There's a tiny vent fitting on the top of the tank. With a vent hose. I can take the hose off, and use the wand on my oil-change pump to pump fluid from the center tank. I pumped out something like 10 gallons of fuel, and the pump started gurgling because the level had fallen and the pump was only getting air.
I pushed the wand in exactly one more inch. Pumped out another eight to ten gallons of fuel. The third round — I'm now down to about 4" — I got another eight to ten gallons of almost entirely fuel. The fourth round — 5" in — I get water!
I pumped until I get down to air, and most of what I got was water. Water with a little bit of fuel. At this point, there are still traces of fuel in the center tank. If I'm right, and it's the source of diesel in the deep bilge, I won't see anything for the next few years. Then, perhaps, traces of diesel once the tank is full again.
I'm wrong and the fuel is coming from a massive hole somewhere else. A hole that only seems to leak when we're under way. A leak that doesn't let fuel into the pan under the engine, but somehow lets fuel into the deep bilge. And it's not leaking onto the floor of the pass-through. Nor is it visible on the sides of the hull above the bilge. Somehow it's leaking in a way that means it's only visible on the top of the center fuel tank.