Aluminum tank installation without foam.

[Stuart Cooperrider]

The folks who are fabricating my new aluminum tank referred me to David Pascoe's article on installation which warns against using foam.
(www.yachtsurvey.com/fueltank.htm) Here-to-fore I've been planning to use foam as per the quidelines from the B-31 tips section . Needless to say, I'm confused. To foam or not to foam? That is the question. Can someone please quide me?
Thanks
-stu

[Carl]

Stu,
I decided to foam in place to evenly distribute the enoumous tank load between the hull and tank. I thought about not using foam but when I ran the numbers I just could not see going any other way. Plus it secured tank in place.

I would rather have tank rot out and leak then burst open or compromise hull, with tank coated as per capt Pats instruction it should be good for many moons. Not saying its right... but was my decision based on what I learned.

Carl

[MarkS]

I have to agree. I put down a fresh 1/2" piece of lexan for the bed and then foamed only the sides and front into place. This made for a little breathing room and still is a snug fit with which I have much confidence.
Again only my $.02
Mark

[CMP]

NO FOAM! You can attach it to the tank pad down low and have them fabricate stand-offs to attach to the stringers between which it sits...

CMP

[MarkS]

Mark,
How about your reasoning behind NO FOAM. After doing as prescribed by Capt. Patrick, I can't for the life of me see why not.
Mark

[Raybo Marine NY]

the opinion of that web site by Dave P is just that, opinion. HIS opinion.
It is not scientific fact.

like when he tries to debunk a moisture meter by having it hovering over a glass of water- the meter reads conductivity that is carried with the wood and the water, so placing a piece of dy wood OVER a glass of water is not enough to say a moisture meter does not work.


I would do the foam partially up the sides.

[Matt29]

Ah, the 'ol foam or no foam discussion. And the debate continues . . .

[Charlie]

NO FOAM
I just finished pulling the tanks from a 20 Shamrock I purchased. The only place the tanks had any corrosion was under the foam. The tanks were zinc chromated before foaming. The tanks were still almost ruined by the foam. This is my experience I will never use foam to hold down an aluminum tank.
CPM is correct. I have seen some fine frabricated brackets for holding the tank in a 31 or a 28B.

[Matt29]

What about the "oil canning" concerns when securing a tank directly to the stringers/bulkheads? This was mentioned by 'lobsta1' on the "Replacement Tank Questions" post.

http://bertram31.com/newbb/viewtopic.ph ... highlight=

Any input on the validity of this concern or ways to address oil canning while securing a tank in a B31/B28 vs B33? I think the install technique would have to be modified a bit to account for the different location/layout of the tank on the 31/28.

I was convinced on pursuing the foaming method on my current tank replacement project until this darned foam/no foam discussion was resurrected once again.

Thanks,
Matt

[CMP]

I install my tanks with 1/4" by 1" wide strips on the bottom of the tank in order to allow air and/or water flow. They are welded to the tank and also serve as attachment flanges on the tank pad. Additionally, I put angle brackets on the top of the tank that extend to the stringers. This is similar to a halo on the head of a person with a broken neck being immobilized. The tank cannot move in any direction, so this oil-canning deal is a non-issue. This also allows airflow, so condensation is not the big issue it can be. As far as foam is concerned, water gets trapped whether from condensation or some other method, then it stays in contact with the metal and the metal fails. It's a fairly simple equation and one that needn't be used. That said, I have only limited experience having seen 10 boats I've disassembled, 7 of which had foamed in tanks. I'm 7/7 on damaged tanks with foam. That's enough for me...

CMP

[Raybo Marine NY]

whats the explanation for tanks that are NOT foamed in failing?

I just removed one of 2 tanks from a diesel powered boat that were 4 years old and failed, no foam anywhere near them.

I also removed another tank this summer from a boat that was 5 years old, no foam in that one either.

There is no blanket statement of logic to apply to this.

There is no oil canning issue with a baffled tank.

The only thing about a 31 bertram in particular is that the stringers do not come up as high as the tank, maybe if some tabs were welded in place on the bulkhead side and another bulkhead properly glassed in aft you could get away with no foam, otherwise the lack of stringer height gets me nervous even with tabs welded along the stringer sides of the tank.