I have a 1995
Catalina 36 Mk II with a surprise
fuel tank. The
survey report indicate one
fuel tank, the manual reports one, and when I went to fill the
tanks I discovered two deck-fills, and two
fuel vents, and when the
boat bounces at sea, one of the
fuel vents sputters
diesel.
I investigated further, and found that a small
storage compartment had been replaced with another 20 gallon tank. The new tank is directly below the original tank.
The fuel drain from the upper tank T's into what appears to be a fuel drain from the lower tank before going (combined) to the
Racor filter. I say "appears" there because the "drain" is on the top of the lower tank. I'm guessing that the "drain" contains a tube that runs to the bottom of the tank such that it can be sucked out. There is also a hose running from the injector assembly of the aft-most cylinder back to the top of the lower tank. I have no idea what that hose is for. The lower tank also has its own fuel vent line (on the top).
I'm guessing that as long as there is fuel in the upper tank, the lower tank will be completely full. Fuel will drain from the upper tank into the lower tank, displacing the air that will escape through the fuel vent. The fuel will then flood into the tank vent and rise until it is at the level of the upper tank.
This system is problematic because it appears as though the lower tank will almost always be full, and
diesel will always spill out of the fuel vent. I also have no idea what that second hose is running from the
engine to the top of the lower tank.
Does anyone know what the second hose might be?
Would it be reasonable to place a fuel valve on the lower tank's vent line such that diesel does not spill as the
boat tosses?
When (not if) I forget to open the vent valve before motoring or a hot-summer day, would that represent a hazard?
Can anyone recommend some good reading to better understand things? I'll be looking into
books on
marine diesels in general.
Thanks,
Novice Sailor