Dont know if I posted a response to this or not so excuse me if this is
a repeat.
Rapid filling a tank where the inlet to the tank discharges directly
into the middle of the tank will cause a LOT of foaming in fuel oil.
Better to have the fill nozzle on a tank deliver to the side walls or
better yet to deliver through a tube that discharges BELOW the normal
level of oil.

Foaming coming out the vent can be remedied by installation of a
'bubble trap' on the vent lines. Whats done in industry where
'foam-outs' are common is to put a thin tube inside the vent hose with
the open end of the tube pointing TOwards the tank and the butt end of
the tube in a flange withing the ID of the main vent line (think of a
'pitot tube' inside the vent line). Foam 'breakers' and bubble traps
are installed vertically so that they drain by gravity back to the
tank. The bubbles are 'pierced' by the tube and the 'liquid remnents
of the bubbles' attach to the walls of the inner tube and then by
gravity drain back to the tank.

The real issue here is that you are most probably filling the tank too
fast and are creating a lot of bubbles/foam. If the tanks are usually
'clean' (or are regularly cleaned out) simply extend the tanks inlet
nozzle with a tube that discharges near the BOTTOM of the tank ....
instead of 'splashing' into the top surface level of the fuel. You
cannot do this if the tank contains crud ... can only be done with a
tank that is regularly cleaned out.

:-)




In article
, Dave
Isherwood wrote:

Thanks - that is an interesting idea of just treating the symptom. That will
certainly save the aggravation and certainly a lot cheaper than re-locating
the vent outlets on the tanks.

Dave


"Capt John" wrote in message
...
On Nov 27, 12:22 pm, "Dave Isherwood" wrote:
Boat is a Carver 530 Voyager and with two vents on either side. When I
fill
(even using a normal slow pump) I get diesel fuel venting. Yesterday I
had
to add 200 gal. to each side and venting started after I'd put in 10
gal.
I'm at a lose to understand why this is happening. Foaming seems unlikely
as
it would need to have filled 50% of the tank!

Any ideas of what is going on? Or even better a simple remedy that works!

Thanks,

Dave

Your vent's in the fuel tank aren't positioned properly, or their too
small. One easy thing you can do is disconnect the hoses from the
fittings on the hull and run the lines into the cockpit. Now I know
what your going to say, then I'll be spilling fuel into the cockpit.
But If you set it up so you can place a small bucked under it, or with
a hose attached to the end of the vent line place the hose into a
small fuel tank, you will catch the fuel spill. Toss it back into the
fuel tank when your done, or later on when your done (the slow rate of
flow when you pour that much fuel shouldn't cause any fuel to spill).
It doesn't get much cheaper than that. My boat's set up that way.

John