Quote:
Originally Posted by Tem1514 Mentor
Okay, lets assume that hull has a big hole in it and is full of water with no trapped air pockets, except for the pool noodles. The "big hole" is a result of the top hatch coming off and the boat barrel rolling, filling up with water 
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You already said the boat weighs 8 pounds. Now you need to know how much water it displaces when submerged when sunk with no air pockets.
You can try to calculate this, but it won't be easy. Or you can easily measure it experimentally by submerging the boat in an appropriately sized tank and measuring the water displacement.
Once you know the volume of the water displaced, that is the volume of the boat. You can use that, along with the known weight of the boat (8 pounds) to calculate the required volume of pool noodle to keep the boat afloat. You will need to know the density of the the pool noodle material.
Does that help? Do you need help with that calculation?
Or you can use a fish scale to measure the "weight" of the submerged boat. This is the additional buoyant force required to keep it from sinking. Knowing this required buoyant force, and the density of the pool noodle material, you can calculate the required volume of pool noodle.