Re: How much foam?
Originally posted by PaulKim:<br /> Hi All, plan on adding some foam to my boat. I found an old brochure from 1960 that had the weight. <br /><br />Hull 650 Pounds<br />O/B 375<br />20 Gallons of Fuel 6 X 20 = 120<br />Myself = 165<br />Wife = 130<br />Kids total = 200<br />Miscellaneous Gear =200?<br /><br />Total = 1840 pounds max<br /><br />From other posts, it appears that I need to put in enough foam of about 2/3 the max load. Which would be 1214 pounds.<br /><br />If I use 2 pound foam that would be 20 cubic feet.<br /><br />Please advise if this should do it. Will need to figure out if my little boat has enough room for 20 Cubic feet.
PaulKim,<br /><br />I am no expert, but as I understand it, the idea with foam flotation is to keep the boat at or above the surface if it is swamped or flooded. Also, you do not need to have enough foam to float the full weight of everything, just enough to give enough buoyancy to keep it all afloat. Example...if you had a block of wood that weighed five pounds, you would not need any flotation to keep it afloat because of its natural buoyancy. Conversely, if you had a brick that weighed five pounds then you would probably need 3 or 4 pounds of buoyancy added to make it float. (no arguments on the various specific gravities of some species of wood, nor the S.G. of bricks...this is just an example).<br /><br />Now, in your list above, the fuel is actually lighter than water and gives a slight amount of flotation, the people actually will float on there own as well. Some of the gear (cushions and such) will also float. The hull which is made of fiberglass as said to be only a little denser than wood...such that it will sink, but it doesn't take much additional buoyancy to keep it afloat. The motor of course is very dense and requires a good deal of additional floatation...nevertheless, the motor will displace a certain amount of water and all you have to do is displace enough additional water to exceed its weight and it will float.<br /><br />All of that is a long winded way of saying that you need enough additional buoyancy such that the foam displaces enough additional water(besides what the boat and contents displaced) so that it will all stay afloat. Unfortunately, determining that amount without scuttling the boat would be pretty difficult.<br /><br />That being said, look around at some modern boats of about the same size and shape and look to see how much foam they have. My boat only had foam under the gunwales and about 3 cubic feet under the splash well...plus a few foam 2 X 4's under the deck. Supposedly Glastron would purposely scuttle one boat from each model to make sure that it would stay afloat even if filled with water. My boat and motor weigh well over 1000 pounds but there was probably less than 600 pounds worth of foam flotation (less than 10 cubic feet)...as explained earlier, the boat and the things in it displace a certain amount of water and add or subtract a certain amount of flotation.<br /><br />Hope this helps. I guess the rule would be that a little too much is better than not enough. I would put in as much as I could, as evenly as I could, and as high as I could.<br /><br />Just my $0.02 worth,<br />Joe
