Q. I’m making a pontoon boat from empty 55 gallon drums. How much floatation foam do I need?
A. Each 55 gallon drum requires about 8 cubic feet of urethane foam. Since each cubic foot weighs two pounds, you will need 16 pounds of foam per empty drum. Therefore, it will require about one gallon kit (makes two gallons) per drum.
Q. Is this boat foam compatible with styrofoam?
A. Yes. It will not “eat” or dissolve styrofoam. If you have a large cavity to fill, you can put some chunks of styrofoam in the cavity to save foam.
Q. How do I know how much foam I need to float my boat?
A. Get your calculator ready, you will need it. A cubic foot of polyurethane will float about 60 pounds of “dead weight”. The wood parts of your boat will probably float, so you don’t need flotation foam to offset that weight. The fiberglass parts of your boat will barely sink, so you really don’t need much foam to offset the fiberglass- maybe one cubic foot of foam per two hundred pounds (or more) of fiberglass hull. The metal parts of your boat are what you really need to account for. A small (4-6hp) outboard may weigh 45-55 pounds. A 50hp outboard will weigh about 200 pounds.
So a 16 foot fiberglass skiff with a 50 horse outboard will need about six cubic feet of urethane foam to keep it afloat. A 12 foot plastic kayak will only need one cubic foot. A 30 foot fiberglass sailing sloop with a diesel engine and lead keel would need about 150 cubic feet of foam. Actually, very few 30 foot keelboats have positive foam flotation, but it’s not out of the question- especially when you consider all of the air pockets that would exist, as well as all of the wood interior components that provide some positive flotation.
Q. Do I need to paint or fiberglass over the floatation foam?
A. You probably should. Polyurethane will absorb a small amount of water, because some of the the cells are open (95%+ are closed, though). Painting or glassing will seal the foam and prevent any water absorption. However, it really shouldn’t be necessary unless the foam is constantly immersed in water, such as in a boat with bilges that are always wet. The foam is not UV resistant, so it must be painted if exposed to sunlight.
Q. Is the polyurethane foam resistant to fuel, oil, and solvents?
A. Mostly yes. It is resistant to splashes of gasoline and diesel fuel, although it will absorb a small amount because no pourable foam can be guaranteed to be 100% closed cell. A strong solvent such as acetone or toluene would eventually break the foam down, but it would take a long time.
Q. What is the maximum exothermic temperature that cured polyurethane foam can reach?
A. 250 degrees F.
Q. What is the maximum surface temperature that cured polyurethane foam can withstand before it begins degrading?
A. 200 degrees F. The foam does not ignite. Under high heat and direct flame, it will char like wood. The foam will break down with continued exposure to excessive heat/flame. The damaged area can be repaired by removing the damaged portion and pouring new foam into the void.
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