Is it true that with buoyancy, the weight of the displaced water equals the weight of the complete object, even if only a part of the object is submerged? If so, why, since the weight of a larger object would be greater than that of a smaller one?

Answer 1

It is true if the body is floating.

The force upward from the water is equal to the weight of the water displaced.

If the body is floating, that water weight must be equal to the weight of the body and the body rises in the water until that is true. That is how ships float.

If the total body volume is such that it displaces WHILE SUBMERGED a weight of water exactly equal to the weight of water displaced, the body is neutrally buoyant. If you operate a submarine you work very hard with ballast tanks to achieve this exact equilibrium, not sinking and not floating. If you want to float your submarine on the surface, you blow ballast tanks, or in other words throw weight away, until your weight of water displaced is equal to the now reduced ship weight with some of the ship sticking above water.

Answer 2

Sorry for the long explanation. I am a naval architect and this subject is close to me :)