Sunday, 29 March 2015

Basic Ship Terminologies- Part 1

You don’t really need to think about ships to come up with terms related to them, anything discipline in Science and Engineering, Economics, Finance, Fine Arts, etc. has its own myriad lexicon. Well, just imagine what would it be like if a designer of a car was completely alien with even the simplest of its terms and parts?

So, let us get to some of the basic terminologies associated with any ship:


Hull is basically the main structural component of a ship. It is a watertight component and supports the deck, and the superstructures. It is nothing but a structural beam providing the ultimate mechanical strength to the ship. The part where it meets the water surface is called the waterline. It is comprised of transverse and watertight members called bulkheads, intermediate members called girders, stringers and webs. Also, it has minor structural arrangements called stiffeners, which are used to increase the strength of the hull steel plating. 

The shape of the hull is chosen to strike a balance between cost, function and requirement and other hydrostatic and hydrodynamic considerations. Hulls can be of fine form and fuller form, monohull and multihull, displacement type, semi-displacement type and planning type, etc.


It is the basic structural foundation at the bottom most part of the hull that runs along the ship’s length. It acts like a backbone of the ship. When dry docked, the ship rests on wooden blocks in the dock. It is the keel, which takes up most of the loads in that case. It not only contributes to the global longitudinal strength of the ship, but also takes up local loads. A ship with a weak keel is a design failure.

They are primarily of two types- “flat keel” and “bar keel”, the former being the most common type and the more stable ones , the latter being the ones meant for smaller vessels like trawlers and tugs.


It is the forward-most part of a ship. Well, if you have seen a ship you must have unmistakably noticed the protruding front section of the ship. Bulbous bow (read our advanced article on bulbous bow) is the bulb-shaped or pear-shaped bulging part of ships. It primarily helps in reducing the power required by the engines to propel the ship.


It is the posterior end of a ship. It is located at maximum length of the aft. The design of a stern also affects the efficiency of a ship’s propeller (which you will learn in an advanced level).There can be various cross-sectional shapes of stern. There are two main types of stern designs used in the shipbuilding industry as of now:
  1. Transom Stern
  2. Cruiser Stern

Port and Starboard Sides

Viewing the ship from the aft, the left side of the ship is called the Port side, and the right, is called the Starboard side.

Superstructures and Deckhouses

It is that above-lying structure above the hull which essentially runs from one extreme side to another. It is placed above the two extreme bulkheads horizontally. A deckhouse is similar to a superstructure, except for the fact that, it does not run across the extreme ends of the ship. A deckhouse terminates somewhere within the extreme sides of the deck.

Length Between Perpendiculars (LBP)

Length between perpendiculars or LBP is the measure of the distance between the forward perpendicular which coincides with the intersection of the stem and waterline and the aft perpendicular which passes through the rudder stock.

Length of Waterline (LWL)

The distance between the extreme forward and aft points of the ship, where it intersects the waterline, is called Length of Waterline or LWL.

Length Overall (LOA)

The length between the extreme ends of the ship is called Length Overall or LOA.


A propeller is the component fitted at the aft of the ship, and it helps in propelling the ship forward. It is driven by a shaft, which in in turn driven by the ship's engine. A ship may have one or more than one propellers depending on the type of the ship, and its functionality. Designers and ship operators should always be careful in ensuring that the entire propeller is always immersed below the water surface, in order to be able to operate at its maximum efficiency.


A rudder is the equipment which helps to steer the ship. It is always placed behind the propeller. If you cut a rudder plate along it's length (from forward to aft), you will notice that it is an aerofoil section (like the wings of a plane). The reason behind using an aerofoil section, is that it generates a lift force when any fluid (water or air) is incident on it at a certain angle. This lift force is used to turn the ship.

What comes up in Part 2?

In the next part (read Part 2 here) we shall get acquainted with newer terms that are more fundamental to a designer, and are of utmost important in deciding on the principal parameters of the ship.LSD

Article By:- Subhodeep Ghosh

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