[masraum]

Originally Posted by RobFrost

If you ignore the buoyancy of the ship and consider pure gravity, the ship will weigh less down there because some of the earth's gravity is in the water which is now above the ship, the gravity of the water thereby now acting upwards upon it.

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I don't think there's going to be enough water to cause much, if any impact to the weight. The diameter of the earth is ~7900 miles. The deepest part of the ocean is almost 36,000 feet, so roughly 7 miles. I don't think 7 miles of water is going to be enough to counteract 3950 miles of "earth".

Originally Posted by hbueno

The mass doesn't change, obviously, but the weight (force) would be less due to buoyancy.

I don't think there's going to be much effect due to bouyancy on an iron/steel ship at the bottom of the ocean (assuming all hollow spaces have filled with water).