Boats and Boatbuilding

I

Introduction

Boats and Boatbuilding, types and construction of any small, waterborne vessel that displaces and excludes the water surrounding it. Traditionally, boats were distinguished from ships by size—any vessel small enough to be carried aboard a ship was considered a boat. Today, the boundary between boats and ships is no longer defined with precision. Some larger vessels are called boats, although they are longer than some ships. This article focuses primarily on the design and construction of craft less than 20 m (65 ft) long. For a discussion of the history of all waterborne vessels, see Ship.

Boats are classified primarily by method of propulsion—for example, sailboat, motorboat, and rowboat. They are also classified according to function, method of construction and type of materials used, rigging (in sailboats), and other factors.

II

Basics of Boat Design

Only a few basic components are common to most boats of traditional style. The keel is a timber or other element running the length of the bottom of a boat along the center from the bow, or front, to the stern, or rear. The keel serves as the foundation for the frame, which is covered with a waterproof material to form the hull—the body of the boat. The terms keel, frame, and hull are also used in describing modern boats that are not built but are molded in one piece.

A

Buoyancy and Weight

For an object to float on the water’s surface, it must sink enough to displace a volume of water equal to its own weight. For example, if a boat is to carry three people, their fishing gear, an outboard motor, and a supply of fuel—a total weight of about 500 kg (1,100 lb)—then the boat must be made long and large enough to displace 500 kg (1,100 lb) of water without sinking below the water level. Boat designers also have to take into account the weight of the boat itself. The heavier the material used to build the boat, the larger the boat has to be.

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B

Trim and Stability

In addition to considering the total weight of the boat and its contents, boat designers must also consider the distribution of weight. The weight of an outboard motor at the stern of a small boat tends to make the boat sink deeply in the water at that end (to “trim the stern”). If that tendency cannot be offset by placing a similar weight in the bow of the boat, then the offsetting must be obtained by broadening the hull at its aft, or back, end so that a greater part of the displacement occurs near the excess weight.

A balance of weights from side to side must also be arranged. Further, to lessen the danger of capsizing, the combined center of gravity of all weights must be sufficiently low in the boat. If other factors make it necessary that the center of gravity be high, then the chance of capsizing must be offset by increasing the width of the hull.