Foaming Tanks In Place

[Lojanica]

1st off ya'll been incredibly helpful in my refit of a 43ft cutter rigged s/v.

I am now nearly ready to install my new tankage after gutting the cabin and tabbing in new tank dividers and cabin sole supports out of coosa.

The tanks are poly. I was hoping to use foam as space filler and to give support to the tank beds. I have heard that 2 part pour foam is not great and that styrofoam peanuts in plastic bags may be a better solution as they do not absorb water.

What about styrofoam peanuts in a bunch of small trashbags and then a small amount of pour foam to fill up the small remaining area.

I am looking for ideas. What would any of you do?

Thanks.

[lateral]

We have just done our tanks which were SS encapsulated with epoxy. Reason being that they had some fine perforations where they had previously beeen supported with rubber buffers.(Crevious corrosion)
Anyhow, we laminated some good quality SS tie-down webbing to the hull making sure there were no hard spots on the lamination/webbing transition, using flexible epoxy, with a rachet to tighten other end. Worked well for us with rigid tanks and gave us some extra stowage next to tanks. The actual "bed" we made out of West 410 (super slow hardener because of bulk) and sat the tanks in strips of it.
I wouldn't use pour in foam as too low density & will make a mess eventually.
How rigid are your polyprop tanks?

[roverhi]

The problem with two part foam is it expands with a lot of force. You have to be very careful not to pour too much in or it can collapse what it surrounds or pop it out. Just got through tearing out an ice box that was set in two part foam. It seemed to have worked fine as there were no voids below and outboard of of the box where it was foamed. If you are poring it around a tank, brace the inside of the tank if possible

Do not foam in a metal tank. Last boat had aluminum tanks foamed in. Water seeped in and corroded the bottom/backs out of the tanks. Literally 12" roundish circle with nothing but aluminum oxide, no metal.

[Lojanica]

Originally Posted by lateral

How rigid are your polyprop tanks?

The tanks need much more support than metallic tanks as they are not very strong.

That's why I was thinkink styrofoam peanuts/beads and a small amount of pour foam to fix the styrofoam together as a block. I also think the styrofoam compresses which would keep the area safe as the pour foam expands.

[CarinaPDX]

I foamed in my aluminum day tank with 2-part more than 30 years ago, and it held up beautifully. The force of expansion was not an issue for me; I was prepared to put water in the tank as the foam expanded in order to keep it in place but that was not needed. As for corrosion, it was not a problem on the exposed top of the tank or the sides and bottom against the foam - the tank location was dry. If salt water were to have been in the area I'm sure it would have soaked into the foam and corroded the tank. I did glass over the top edge of the tank and the top of the foam, which provided a good barrier to liquids. That said, I had a stainless steel kerosene tank located on the shelf above the day tank and it did corrode internally and slowly leak kerosene, which soaked the wooden bulkhead and much of the foam around the day tank. Now that was a stinky mess. Ultimately, the aluminum tank was corroding on the inside at the very bottom from water and dead algae - the outside never became a problem.

Most poly tanks in the US are not sold these days for diesel, I think because they do not meet the low permeability standards. IIUC the rotomolded fuel tanks have a low-perm coating on the inside; the welded poly tanks don't. Also, there are thermal expansion issues with using metal fittings with tapered threads into poly tanks, so appropriate plastic fittings should be used. The European metal fittings with (somewhat loose) straight threads and gasket seems a lot better. Reluctantly I will be having another aluminum tank made.

Greg

[minaret]

There is more than one flavor of pour foam. Higher density pour foam is much less water absorbent and obviously much stronger as well. Try this stuff, I would go with 4lb (which is made for supporting tanks) or maybe even 8 lb. if it's a big tank and you are really worried about supporting it well. If you do 8 lb. hope you don't ever have to remove it. Whatever you do don't use 16lb, you need a jackhammer to remove that stuff. The regular pour foam most people use is 2 lb. density...


Urethane Foam , Expanding Marine Polyurethane Foam

[GordMay]

Cellular plastic (foam) may provide the only support for non-metallic fuel tanks. In order to use foam as the only support for these non-metallic tanks, the foam must meet or exceed the requirements of 183.516(b) or (c):
B - non-polyurethane foam compressive strength of at least 60 pounds per square inch at 10 percent deflection
C - for polyurethane foam a density of at least 2.0 pounds per cubic foot.

Cellular plastic used to encase fuel tanks
➥ §*183.516***Cellular plastic used to encase fuel tanks. :: PART 183--BOATS AND ASSOCIATED EQUIPMENT :: CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY :: Title 33 - Navigation and Navigable Waters :: Code of Federal Regulations :: Regulations

And ➥ http://www.uscgboating.org/regulatio...rds_partj.aspx

[Lojanica]

One interesting tip I received was to get HEAVY plastic bags garbage bags and fill 25% or so with true styrofoam peanuts or beads used to fill bean bag chairs which allows you to "squish" the bag into the perfect location and then to use small amounts of the "heavy" 4 or 8 lb pour foam to bond it all together. I guess the rationale is 2 fold---styrofoam does not absorb water, and poly does not dissolve with diesel?!? Also the heavy garbage bag somehat insulates the foam from intrusion anyways.

Not that I am gonna have any diesel or water leaks ; )


All good ideas. THANKS!!!

[Lojanica]

Originally Posted by GordMay

Cellular plastic (foam) may provide the only support for non-metallic fuel tanks. In order to use foam as the only support for these non-metallic tanks, the foam must meet or exceed the requirements of 183.516(b) or (c):
B - non-polyurethane foam compressive strength of at least 60 pounds per square inch at 10 percent deflection
C - for polyurethane foam a density of at least 2.0 pounds per cubic foot.

Cellular plastic used to encase fuel tanks
➥ §*183.516***Cellular plastic used to encase fuel tanks. :: PART 183--BOATS AND ASSOCIATED EQUIPMENT :: CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY :: Title 33 - Navigation and Navigable Waters :: Code of Federal Regulations :: Regulations

And ➥ Deprecated Browser Error

Gord,

When I read this it would seem that the styro- pu pour foam combo is within regs for holding PTFE tanks in place.

THX

[Lojanica]

Again thx for all the tips/tricks. So the plan is thus after cajoling with many:

1. Make mold(s) on the hard with the tanks out of the boat. Undersize the completed foam blocks so they easily slip into the hull. I only need to make 2 molds.

2. Mix styrofoam peanuts and the 8 lb foam pour foam and cast the blocks.

3. Trim, Shape, and add limber holes as necessary.

4. Coat lightly with epoxy.

5. place under tanks as bedding.

6. Shim if needed and cleat sides and top.

Regards