Buoyancy, the idea behind how hundred-thousand ton freighters can float, is a force based on displacement. If you displace a gallon of water, you get that much buoyancy. The buoyancy force is equal to the (weight)x(amount) of whatever you are displacing. The math in my example is simple. A gallon of water displaces a gallon of water. So the gallon of water weighs 0 pounds in the water because it displaces the exact amount and weight of itself. So pick any gallon of water in the ocean, it weighs 0 pounds. If every gallon of water in the ocean weighs 0 pounds, than the whole of the oceans weigh 0 pounds. All our oceans are weightless, why don't they float away?