Adding floatation

[timnphx]

I recently made some slight modifications to my boat (12.5ft row/sail boat) where I created some areas under the aft seat and side seats where I poured in the 2-part foam that swells to about 20x its volume in about 1 minute then drys in about 5 minutes but then creates added floatation to your craft. I was able to get in approx 1.5 cubic feet. I hope this is enough to have a positive float if ever was to turn her over. Any thoughts on this issue :?: :idea:

[umop_apisdn]

ooo! Physics questions! :-)

Water weighs between 62 and 64 lbs per cubic foot, depending on how much salt is in it. So you added about 90 lbs of floatation.

That is probably enough for a row/sail boat, depending on what your hull is made out of, how dense the stuff in your boat is, and how much falls out (or you are willing to toss overboard) in the event you overturn or swamp it.

If you had a heavy motor firmly bolted to your transom, and batteries that are tied down so they can't fall out, you would probably want another cubic foot or so of floatation.

Noel

[PAR]

Much depends on the density of the foam (there are different densities) The stuff I use comes in three densities. A 2 pound foam will make 8 cubic feet from a two gallon kit, supporting about 480 pounds. The 4 pound, two gallon kit will make about 4 cubic feet and support 230 pounds. The 8 pound stuff (also a 2 gallon kit) makes around 2 cubic feet, supporting about 110 pounds.

Placement is also important, the boat should support your weight while swamped or laying on her side, without sinking. This usually means placing the floatation in the sides of the boat, up near the deck or gunnels level. Quite a few manufactured small sailboats have floatation chambers built in under the side deck or sitting areas, for this very reason. Weight your boat, include your crew weight (this includes coolers of beer) and add a 10 to 15% margin for safety.

[Greg Luckett]

If you want' date=' I could dig up and provide you the Coast Guard required formulas for determining how much floatation foam is required fo builders of commercially sold recreational power and row boats under 20 feet.[/quote']

Ray,

This would be useful to have. Is there an online link to it?

Thanks.

[timnphx]

Ok, well i may have answered my own question a bit by re-visiting the website and seller of the 2-part foam I purchased (John Greer & Associates). I have pulled in a bit of his website question and answer so this is what he wrote;

Q. How do I know how much foam I need to float my boat?

A. Great question! Get your calculator ready, you will need it. A cubic foot of foam 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 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.