Why does a canoe float?

Why does a concrete canoe float?

• Answer:

  Any boat made of a heavier than water material can float if it meets a few basic requirements. The first requirement is that the total volume of the boat must be greater than the weight of water that volume would displace. The second requirement is that the boat must not permit water inside. There are additional details but these two are the biggies. Here is an example: A 20 foot canoe has an overall displacement (volume) of 40 cubic feet. That is equal to approximately 320 gallons, or a weight of 2,560 pounds. Concrete weights vary somewhat but using a number of 150 pounds per cubic foot, as long as the total amount of concrete used is less than 2,560 / 150 or about 17 cubic feet, the boat could float. If the sides and bottom of the canoe are 2 inches thick and the bottom area is 50 square feet and the sides also total 50 square feet, 100 square feet total times 2/12 foot thickness gives about 16.6 cubic feet of concrete. This would just barely float.