help with materials evaluation

r1ley

I'm in the process of designing and building an aluminum boat. Typically a piece of .125 thickness 5086 alloy aluminum is used for the hull and it is braced with 4 separate .125 x 1 x 1.5" square tubing sections which run the length of the boat and are stitch welded to the bottom. On top of this a thinner sheet of aluminum is generally riveted to the pieces of tubing to form the "floor" of the boat which is walked on.

My idea is to replace the reinforcement tubing by welding the floor to the sides of the boat essentially forming a piece of 1.5" x 40" (the boat bottom width is 40") and filling the void in between the two sheets of aluminum with high density expanding foam. When expanded the foam will place outward pressure on the aluminum and reinforce it.

Here are the specs of the foam:

*Physical Properties:
Parallel Compressive Strength: 250 psi
Tensile Strength: 225 psi
Shear Strength: 130 psi
Flexural Strength: 350 psi

Is this possible? Can anyone compare the flexural strength I will get with the aluminum tubing vs just the foam?

My thinking is that it is similar to concrete in flexural strength and tensile strength, so it would need some reinforcement, but would having it in a sealed container under pressure not provide the reinforcement it needs?

Concrete:
Compressive strength : 20 - 40 MPa (3000 - 6000 psi)
Flexural strength : 3 - 5 MPa (400 - 700 psi)
Tensile strength : 2 - 5 MPa (300 - 700 psi)

Anybody who can help me would be much appreciated!!

I attached a crude diagram to help explain the design

Attached Thumbnails