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 front railings of a yacht is called the bow
A ballast
The bottom part of a cake is called the base.
The sails or the engine, depending on the yacht.
Denominator. The top part is called the numerator.
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
It's called a yacht.
They're called udders. :-)