A lot of production builders foam in their tanks. It is less expensive
and quieter. One thing about regulations. If you don't like one you
can probably find another that says something different. And if you
can't find one you can lobby your congressman to create one more to your
liking. :-) In this case 33 CFR 183.516(c) says you can use
polyurethane foam with a density of at least 2 lb./cu. ft.

No regulation is going to suspend the laws of chemistry and physics
however. Urethane can absorb water up to 7% of its weight. Once it
gets inside those cells it does not circulate and eventually runs out of
oxygen.

There is some validity to the argument that aluminum is better than
stainless for diesel tanks. Stainless requires that the chromium oxide
surface be constantly renewed while, though it sounds counter intuitive,
with aluminum the surface corrosion itself inhibits further corrosion.

Bryan B wrote:
Hi Glenn,

Thats what I have read also but the other two tanks are foamed in. The boat
was built by the Bruckamn yard of C&C, which was the custom yard. I thought
maybe there was a foam that was breathable and used for this application.

Confused in Ohio.

Bryan

"Glenn Ashmore" wrote in message
news:mczjb.78272$sp2.67348@lakeread04...

Now THAT is one thing I can definitely quote chapter and verse because
everything I have ever seen says DO NOT use foam around a metal tank.
Especially a stainless one. It will hold oxygen depleted stagnant water
against the metal and create ideal conditions for crevasse corrosion.

Stainless needs a constant supply of oxygen be it in air or desolved in
seawater to maintain the protective surface. Tanks should be mounted so
that air can get to all surfaces. A lot of small Neoprene pads is
better than having the tank rest on a large surface that impeeds
circulation.

While I do not agree with David Pascoe on some things he has a good
section on mounting metal tanks on his survey page.

Bryan B wrote:


I need to re-install a diesel tank. It was foamed in place and an then

tab

glassed to the top of the bulkhead and hull. No problem with the glass

work

but what foam should be used for the tank. The tank is 316 ss about 30
gallons.

Thanks,

Bryan



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com





--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Ever hear of poultice corrosion? It's another reason why aluminum isn't
necessarily better than mild steel.

Glenn Ashmore wrote:

A lot of production builders foam in their tanks. It is less expensive
and quieter. One thing about regulations. If you don't like one you
can probably find another that says something different. And if you
can't find one you can lobby your congressman to create one more to your
liking. :-) In this case 33 CFR 183.516(c) says you can use
polyurethane foam with a density of at least 2 lb./cu. ft.

No regulation is going to suspend the laws of chemistry and physics
however. Urethane can absorb water up to 7% of its weight. Once it
gets inside those cells it does not circulate and eventually runs out of
oxygen.

There is some validity to the argument that aluminum is better than
stainless for diesel tanks. Stainless requires that the chromium oxide
surface be constantly renewed while, though it sounds counter intuitive,
with aluminum the surface corrosion itself inhibits further corrosion.

Bryan B wrote:

Hi Glenn,

Thats what I have read also but the other two tanks are foamed in.
The boat
was built by the Bruckamn yard of C&C, which was the custom yard. I
thought
maybe there was a foam that was breathable and used for this application.

Confused in Ohio.

Bryan

"Glenn Ashmore" wrote in message
news:mczjb.78272$sp2.67348@lakeread04...

Now THAT is one thing I can definitely quote chapter and verse because
everything I have ever seen says DO NOT use foam around a metal tank.
Especially a stainless one. It will hold oxygen depleted stagnant water
against the metal and create ideal conditions for crevasse corrosion.

Stainless needs a constant supply of oxygen be it in air or desolved in
seawater to maintain the protective surface. Tanks should be mounted so
that air can get to all surfaces. A lot of small Neoprene pads is
better than having the tank rest on a large surface that impeeds
circulation.

While I do not agree with David Pascoe on some things he has a good
section on mounting metal tanks on his survey page.

Bryan B wrote:


I need to re-install a diesel tank. It was foamed in place and an then


tab

glassed to the top of the bulkhead and hull. No problem with the glass


work

but what foam should be used for the tank. The tank is 316 ss about 30
gallons.

Thanks,

Bryan



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com