Oceania

A hull is the body of a ship or boat. It is a central concept in floating vessels as it provides the buoyancy that keeps the vessel from sinking.

Nearly all watercraft, from small boats to the largest ships, adhere to a general form that serves the needs of stability and efficient propulsion, featuring:

• horizontal cross-sections that have narrow, usually pointed, fronts (at the bow),
• smooth widening from the bow until roughly the middle of the length (midships), and often narrowing smoothly but usually significantly to the extreme end (the stern), whose width may range from a large to an insignificant fraction of the beam.

Hull Shape

Hulls come in many varieties but are grouped primarily as follows:

• Moulded, round bilged or soft-chined

defined as smooth curves

• Chined or Hard-chined

have at least one pronounced knuckle throughout all or most of their length

After this they can be categorized as:

• Displacement

the hull is supported exclusively or predominantly by the pressure of water displaced by the hull

• Semi-displacement, or semi-planing

the hull form is capable of developing a moderate amount of dynamic lift, however, most of the vessel’s weight is still supported through displacement

• Planing

the Planing Hull form is configured to develop positive dynamic pressure so that its draft decreases with increasing speed. (see: Planing (sailing)).

The inverted bell shape of the hull, with smaller payload the waterline cross-section is less, hence the resisitance is less and the speed is higher. With higher payload the outward bend provides smoother performance in waves.

Many hulls have composite shape, e.g., a fine entry forward and inverted bell shape aft.

Appendages

• A protrusion below the waterline forward is called a bulbous bow and is fitted on some hulls to reduce the wave making resistance drag and thus increase fuel efficiency. Bulbs fitted at the stern are less common but accomplish a similar task. (see also : Naval architecture)

• A keel may be fitted on a hull to increase the transverse stability, directional stability or to create lift.

• Control devices such as a rudder, trim tabs or stabilizing fins may be fitted.

Terms

Bow is the frontmost part of the hull

Stern is the rear-most part of the hull

Portside is the left side of the boat when facing the Bow

Starboard is the right side of the boat when facing the Bow

Waterline is an imaginary line circumscribing the hull that matches the surface of the water when the hull is not moving.

Midships is the midpoint of the LWL (see below). It is half-way from the forwardmost point on the waterline to the rear-most point on the waterline.

Baseline an imaginary reference line used to measure vertical distances from. It is usually located at the bottom of the hull.

source : en.wikipedia.org