a Hull
Ballast
The main part of the boat that you walk on is called The deck. Usually known to have the best view on the boat.
The top part of a wave is called the crest, while the bottom part is called the trough.
the front railings of a yacht is called the bow
The bottom part of a cake is called the base.
A ballast
Denominator. The top part is called the numerator.
The sails or the engine, depending on the yacht.
it depends what you mean by the bottom part.... are you talking about the stem, roots, ect?
Hem.
a bottom (body part) is called 'un derrière' (masc.) in French
The bottom part of your hand is the Palmar sideand the top part is the Dorsal side.