Boat hulls are currently usually made of fiber glass. Fiber glass is the cheapest, most effective material. Boat hulls can also be made of wood, carbon fiber, and steel.
A Trimaran is a boat with three hulls.
A trimaran has 3 hulls, a main hull and two smaller outrigger hulls.
Trimaran
This type of boat is called a Catamaran.
Usually they are made of fiber glass, but they can be made of other materials (wood, steel, carbon fiber, etc) as well.
Catamaran.
A trimaran is a sailing yacht with three parallel hulls.
4
Tri-hull
Trimaran
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There's no law against it, but it will slow your boat down.