Need A Little Advice On Floation Foam

ok i'm gettin ready to restore my 1961 lonestar aluminum skiff, its 16ft LOA with a 65in BEAM. i am wanting to fill the hull with foam under the floor to help bouyancy for the weight im adding with the 70hp motor, 20gal tank, center console and 7ft casting deck im adding to the front. my question is will this help keep my boat from drafting deeper and also how should i distribute the weight throughout the boat?

Re: Need A Little Advice On Floation Foam

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.

In addition you might read this
http://www.glen-l.com/weblettr/webletters-7/wl55-flotation.html

Re: Need A Little Advice On Floation Foam

Adding foam under the deck will not add boyancy to the boat under normal operating conditions and will not make the boat ride any higher in the water. It will only help keep the boat afloat if the boat is full of water.

Re: Need A Little Advice On Floation Foam

Robert4Winns said:

Adding foam under the deck will not add boyancy to the boat under normal operating conditions and will not make the boat ride any higher in the water. It will only help keep the boat afloat if the boat is full of water.

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Exactly. The fatal flaw with OP's plan. There is nothing you can add to the boat to increase buoyancy under normal operating conditions, when water is outside the boat. Anything that is heavier than air will DECREASE buoyancy under normal conditions

Re: Need A Little Advice On Floation Foam

Correct, the boat only sees the foam as weight, it doesn't know foam floats and as additional weight it will make the boat have more draft, although 15-20 lbs of foam can't make that much difference in draft.

I get this question all the time in the pontoon buisness, people want to put air in there tubes to make them float better but of coarse the only way to increase bouyancy is to reduce weight or increase hull size.

Always good to have flotation foam btu not for the reason you want it.

Re: Need A Little Advice On Floation Foam

i read some where that people build small boxes on each side of the transom, and fill with foam and it helps draft and getting on a plane.

Re: Need A Little Advice On Floation Foam

thanks everyone for your imput on my questions, i got the info i've been wondering about. so there isn;t any reason for me to spend all the extra cash loading my boat down with foam. only other question ive got is how evenly distributed should the weight be in my boat so i get the best ride possible?