[Destroyer]

Originally Posted by tartuffe

I believe you need to check your math. Try hooking 5 noodles to your motor and tossing it in the water and tell me what will happen. That 200 pounds is based on the difference of the weight of water and the weight of a person for the same volume of water. In reality, you are probably only looking at 15 pounds of buoncy (sp?) per noodle.

Hmmmm...how to answer this?.... Ok, lets try this.. You have a 12 lb rock, and you lower it into water on a string and find it weighs 8 lbs. (roughly a 33% reduction in weight) Now you take a 4 lb block of lead and lower in into the same water and you find that it weighs 3.64 lbs (roughly a 9% reduction of weight) Why the difference? Lets look at the math.
4 lbs of lead X .4536kg/lb = 1.814kg x 1000g/kg=1814.4g. This is weight of the lead. So the density of lead is 11.3437g/cc
What is the volume of the 4lbs of lead? 1814.4g /11.3437 = 159.94 cc (That's the volume of water that the lead displaces.)
How much does this water weigh? It varies..the density of ocean water is 1.027 g/cc (fresh water is 1.0 g/cc) so 159.94cc ocean water X 1.027 g = 164.26g (That's the amount of positive buoyancy applied to the lead when it is submerged.)
Now, converting back to lbs, 164.26g = .16426kg /.4536 (kg/lb) = .3621 lbs
So the weight of the submerged lead is (4 - .3621) = 3.64lbs
The reason for the difference is the density of the two objects. Lead is much denser and so it displaces less water and is less buoyant than the rock. So too, the noodle will support an average 200 lb person in much the same way that a life jacket filled with foam will, because the human body is much less dense (and so has more positive buoyancy) than an outboard engine or a fiberglass boat. As to boats, a cubic foot of polyurethane (closed cell foam)will float about 60 pounds of "dead weight". The wood parts of a boat will probably float, as well as the gas tank(s), so you don't need flotation foam to offset that weight. The fiberglass parts of a 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 the 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 about one cubic foot. Conversly, 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). As far as our V20's and V21's go, I really don't know exactly how much foam it will need in terms of cubic feet. But I figure that Wellcraft's engineers did know when they started adding foam into the boats. By law they had to put enough foam in place to support the boat, gear and engine. So I intend to mimic the amount they used as closely as possible in the compartments, and then add additional foam in the gunnels and other places to make up for any loss due to voids between the noodles. But as far as the original statement goes, 2 boxes (40 pcs) of noodles should support 8000 lbs of human density weight, since each noodle is rated for 200 lbs of floatation. (200 lbs x 40pcs = 8000lbs). I'm fully aware of the differences of density vs volume. Maybe I should have made it a little clearer but hopefully you understand what I meant in my original statement a little better now.