Hull type

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Hull Type

Ships are often categorized by their hull type. This can often include elements of hull form as well. Some methods of classification;

Contents

Number of Hulls

A typical vessel will have a single hull, and is known as a monohull. More exotic vessels can have multiple connected hulls - catamarans have two, trimarans have three, pentamarans have five - collectively, they are known as multihulls.

Distribution of Displacement

The hull may have a ship shape, where displacement increases towards the top of the vessel (flare above the waterline). Alternatively, the hull may be a whaleback or similarly have decreasing displacement above the waterline (tumblehome, often seen on concept designs such as those with wave piercing or reduced radar cross section hulls.) Displacement may be neutral, as in submarines, or primarily below the waterline as in SWATH, SLICE, and semisubmersible hulls.

Buoyant Support

There are three primary methods a hull derives the lift necessary to keep 'afloat'. These are:

  1. Hydrostatic - also known as displacement hulls, also traditional submarines.
  2. Hydrodynamic - A force is generated by water moving over lift surfaces. This includes planing vessels & hydrofoils.
  3. Aerostatic - The force of air, either captured (air cushioned vehicle) or layered (surface effect ship or wing-in-ground effect).

These classifications are not exclusive - there are, for example, semi-planing hulls where the developed lift is a fraction of the vessels displacement, and most vessels are not exclusively hydrodynamic or aerostatic. These modes of operation require continual power application, so most dynamically supported vessels have sufficient stability and displacement to operate in a hydrostatic mode.

Shape

While some of the aspects above will lead to particular hull shapes (i.e., a planing hull will have flat, lift-generating, sections aft), hulls can be broadly classified by notable shapes of the bow (X-bow, axe bow, spoon bow, white bow), stern (cruiser stern, transom stern, counter stern) or sectional development (chines, round bilge, cathedral hulls).

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