[masraum]

Originally Posted by javadog

You guys are getting sidetracked. Weight is a measure related to two things, mass and strength of the gravitational field where the mass is. The mass of the ship doesn’t change, but the gravity constant does.

Buoyancy, density, salinity of the water, all that is just irrelevant nonsense.

Right, mass wouldn't change. Gravitational constant changes with altitude. Since we are talking about weight, if you could balance the ship on a scale at the bottom of the Mariana Trench, due to the relative densities of sea water and the materials that the ship is made of would see a change due to bouyancy. If the ocean was Mercury, the ship would never sink.

One point of view, no mass change, so weight would only change due to change in altitude.

Second point of view, assuming no bouyancy due to air pockets, then the material of the ship itself would have some bouyancy (even if it didn't float) and hence the weight would be decreased due to that bouyancy, despite the weight increasing due to change in altitude.

That's how the specific gravity of solids with a specific gravity (relative density) >1.0 is measured. A sample is submerged in fresh water and weighed. The weight is decreased by a certain amount, and that amount gives you them relative density.