1.1 Ship description and General Arrangement
A merchant ship or vessel transports goods or cargo, vehicles and or passengers by sea.
The layout of a ship is described as the general arrangement plan, showing the division of a vessel into compartments.
These compartments are formed by longitudinal and transverse vertical separations - bulkheads and horizontal separations, the decks.
On board, we can therefore divide each element into a separation or space.
The outside of the vessel is the hull, the main body that allows the ship to float.
The fore part of the vessel is the bow (pronounced “baô”).
To increase efficiency, many ships have a bulbous bow, featuring a spherical shape to the submerged part. The bow structure above the waterline is the prow.
The space inside the fore part of the hull is the forepeak.
The foremost part of the upper deck is called the forecastle (pronounced “foksel”).
The anchor winches are situated on this deck.
Forwards, the anchor chain is stored in the chain locker, situated over the forepeak tank.
Extensions of the plating above the deck are called bulwarks.
The middle section of a vessel is known as the middle body.
The top, flat section of the vessel is the main deck.
This is exposed to sea and weather which is why the main deck is also called the “weather deck”. It must be weathertight in order to protect the cargo.
The tween deck is an intermediate deck between upper and lower decks.
Dry cargo is carried in holds, liquid cargo is contained in tanks. These holds, or tanks, are separated by transverse bulkheads.
The main deck is fitted with openings called hatches to access the cargo holds. These hatches are closed with watertight hatch covers which may be sliding or retracting.
The hatches must be sufficiently wide for grabs or cranes to load and unload cargo.When a ship is sailing partially loaded or without cargo, some weight must be loaded for the ship to be seaworthy.
This extra weight is called ballast. For that purpose, seawater can be pumped into ballast tanks and the double bottom of the hull.
The double bottom provides strength and storage space for fuel, lubricating oil, fresh water, salt (ballast) water. This type of construction also reduces the chance of flooding in case of damage to the outer hull plates.
To prevent liquids from leaking from one tank into the other, longitudinal and transverse separations are used to divide the tanks.
These separations, creating empty spaces, are called cofferdams.
Above the main deck we find the superstructure with the accommodation for the crew and passengers, the mess room, the galley and the pantry.
On the top floor of the superstucture is the bridge where officers oversee the operations of the vessel as well as steering the ship and navigation.
Bridge wings allow better visibility for maneouvring, loading and unloading.
The navigation and communications equipment is usually situated on the monkey island, a small deck or platform above the bridge.
The space below the accommodation is commonly dedicated to the engine room.
The engine room is a watertight machinery space that contains the vessel’s propulsion plant.
The steering room must also be a watertight compartment and is very often situated over the after peak tank.
The power of the main engine is transferred to one or more propellers or screws which push the ship through the water, turned by the propeller shaft.
A ship with one propeller is called a single-screw ship. Ships with two propellers are called twin-screw ships.
For the ship to be steered, it is fitted with a rudder.
Exhaust gases from the engines are expelled through the funnels.
The centreline along the bottom of the hull is reinforced by the keel.
The aft section of the hull is known as the stern.
Many hulls have a flat section, known as a transom. Ships also often have a deck above the stern, aft, the quarterdeck. On many merchant ships, the lifeboat is situated aft above the stern.