[Public-List] gas tank replacement

[Stephen Gwyn]

So this is going go a bit long.

I replaced my tank a few years ago. The tank I removed was not
original, so it's unlikely to be the same dimensions as yours.

I measured the tank several times and concluded that there was no
way it was going to come out with the engine in place. I made a
cardboard template of the end of the tank and tried angling it
different ways. No chance. Since I didn't want to remove the
engine, I went sideways.

I removed the plywood bulkhead between the engine compartment and
the port locker. This is a lot less work than you think it might
be. There are a few fasteners, a mixture of screws and pop rivets
but they were easily removed. The bond between the fibreglass
deck molding and the plywood bulkhead had long since
deteriorated. Wood almost always ends up separating from glass
because they expand differently with temperature and moisture
changes. I used the curved end of a thin crowbar to gently tweek
the few remaining sections where the bond was still almost good.

The main problem was I did this in a Pacific North West winter, so
the plywood had expanded so it was wedged between the forward
bulkhead (between the locker and the cabin) and the aft
bulkhead (between the locker and the lazerette. It took a few
very careful whacks with hammer to get it out.

Once bulkhead was out, it was pretty easy to remove the tank
itself. It would have been even easier if it was completely
empty.

I bought a custom new one made in aluminum from Strait Metals
here in Victoria: $700, but much better made then the previous
one. I'll let you know in 20 years how it lasts. The standard
plastic tanks available either were too small (loss of range) or
too big or the wrong shape (wouldn't fit). No one I contacted was
prepared to fabricate a custom tank out of plastic once they
found out I was going to put gasoline into it.

The ABYC recomendation is that the fuel is not allowed to sit in
the fill hose. My tank lies at angle with the lower end at the
front, which is also the where the fill is. Therefore the tank
has a custom fill spout welded to the top of the tank. At rest in
the boat, the fuel never comes out of the spout. The spout only
just barely fit back in. I had to cut a way a section half an
inch high by 4 inches long in the fibreglass tabbing at the
top of opening

The previous tank was held down with copper strapping (the kind
used in plumbing, the stuff with lots of holes) in contact with
the aluminum tank, which was a mistake. The front bottom rested
on a horizontal bar with a lip to retain water, also a mistake.
I'm pretty sure this bar is fairly standard. It runs side-to-side
behind the engine and is made out of aluminium. The back end just
rested directly on the (often damp) fibreglass of the hull.

The new tank is installed on plastic pads, bonded to the tank
with 3M5200, as per the ABYC guidelines. The plastic pads are a
cut up children's tool table I bought a garage sale because lots
of pieces that looked like the right shape. It's made of
polyethylene. 3M5200 does not stick very well to
polyethylene (nothing does), but that's OK, because it's just
there to keep moisture out from between the pad and the tank.
The pads at the back raise it off the fibreglass. The pads at the
front keep it out of the lip. I replaced the copper strap over
the front of the tank with with stainless steel, isolated from the
tank with another set of 3M5200 and polyethylene pads on the
corners. This strap is bolted to the exising aluminum cross bar.
The strap is tightened at the top of the tank with a long bolt.
The tank is very stable. No amount of my shoving could move it
and it doesn't shift even at extreme angles of heel. If the boat
was inverted, there might be a problem.

Then I reinstalled the vent, the fuel line, and fill hose.  Where
brass meets aluminum, I was careful to use yellow teflon tape.

Finally, I bolted the bulkhead back into place. Again it took a
few whacks to wedge it into place with between the other
bulkheads. Where I could, (i.e. where I could reach the far side)
I through bolted. Everywhere else, I used self tapping screws.

Stephen
#495 Quasar



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Stephen Gwyn                       | Tel: 1-250-363-3136
Canadian Astronomical Data Centre  | Fax: 1-250-363-0045
Herzberg Institute of Astrophysics | Cell: 1-250-885-6969
5071 West Saanich Road             | E-mail: Stephen.Gwyn at nrc-cnrc.gc.ca
Victoria, BC, V9E 2E7, Canada      | http://astrowww.phys.uvic.ca/~gwyn/
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