calculating foam bouyancy

[rebars1]

I picked up a small foam kit that says it creates about 2 cu ft of expanded foam for 100lb of bouynacy. Does that mean it could float 100 lb of weight?<br /><br />If I wanted to put in enough foam to keep a small runabout from sinking, do I add up the weight of the boat, motor, etc. and divide by 50 to get the cubic footage required?

 

[cc lancer]

Re: calculating foam bouyancy

Technically...yes<br />But there is the engine, is it an outboard or inboard?<br />Two pound foam will support up to 60 pounds per cubic foot, or keep a 180 pound man's head above the water.<br />Sinking that another story......going to the bottom like a rock, or part of the boat above water.<br />One of my best friends had a 20 some foot Boston Whaler with a cuddy cabin. The boat had a outboard on it. He was hit just under the water line on the side. When it stopped sinking there was 3 feet of bow sticking out of the water.

 

[ThomWV]

Re: calculating foam bouyancy

Technicall ... no<br /><br />It is not the weight of the boat that matters, it is the weight of water that the sunk boat displaces plus whatever wieight of boat that is held above the water that the foam has to overcome. This is a number that will typically be much less than the actual weight of the boat.<br /><br />Now the foam. How much does the kit weight? I ask because the foam that is produced from it can not weight any more than the kit does.<br /><br />Now, there are 7.5 gallons of water a cubic foot of water. Water weights 8.33 pounds per gallon so a cubic foot of water weighs 62.31 pounds. That means that your 2 cubic feet of foam will displace 124.31 pounds of water minus whatever the kit weighs).<br /><br />Thom

 

[JasonJ]

Re: calculating foam bouyancy

Just go with 8 cubic feet foam per 800 lbs of fully rigged boat weight, that will give you more than enough water displacement to keep the boat from sinking.

 

[rebars1]

Re: calculating foam bouyancy

Does anyone know of a good source for foam? At the rate my local store charges, it will sink my wallet before the boat even gets to the water!

 

[walleyehed]

Re: calculating foam bouyancy

Typical of marine flotation foam........

 

[jimmythekid]

Re: calculating foam bouyancy

www.uscomposites.com

 

[cc lancer]

Re: calculating foam bouyancy

I found this to be interesting calculating weight and buoyancy.<br /> http://www.aquaholic.com/gasses/archem.htm <br />----------------------------------------------<br />Fresh water weight.....62.426 pounds<br />Salt water weight.....64.00 pounds

 

[rebars1]

Re: calculating foam bouyancy

Good tip, jimmythekid, those prices are about 25% of what the local store charges. <br /><br />cc lancer: very good explanation of bouynacy at that web site.<br /><br />I have about 6 cu ft available the stern, and about 2 cu ft at the bow.