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Ship hull structure (part 1)
Words and Terms to be Remembered
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hull |
bulkhead |
Read the text and find the answers to the following questions.
1. What are three main parts of the hull?
2. What members divide the hull into compartments?
3. What cargo spaces are there inside the hull?
4. What kind of tanks are provided on board a ship?
A ship is a floating engineering structure to perform different duties to ensure navigation and shipping. The main body of a ship is called a hull. The hull is divided into three main parts - the foremost part is called the bow, the rearmost part is called the stern, the part in between is called midship. The hull is the main part of a ship. It starts with the stem, ends with the stern frame, and is restricted by the main deck, the bottom and the sides. The hull is symmetrical in relation to the centre (-line) plane. Facing the bow aboard the ship, the left-hand side is the portside and the right-hand one is the starboard side. The upper deck runs continuously along the whole length. Turning of the bottom into the side is known as a bilge. It can be smooth or with a break.
The hull is made up of frames covered with shell plating. Frame is one of the transverse girders forming the ribs of the hull. The part of the hull below water is the ship's underwater body. A part of the ship's side above the waterline is the vessel's freeboard. The hull is divided up into a number of watertight compartments by decks and bulkheads. Bulkheads are vertical steel walls going across the ship and along. They give the ship contour, shape, rigidity and strength. All transverse bulkheads extend athwartships while all longitudinal ones extend lengthwise or fore-and-aft. Bulkheads are reinforced by strength members called stiffeners.
The hull contains the engine room, cargo spaces and a number of tanks. In dry cargo ships the cargo space is divided into holds and tweendecks. Openings giving access to holds are known as hatches or hatchways. Vertical plates edging the hatch along the perimeter above the deck are called hatch coaming. The hatch is closed with a hatch cover. In liquid cargo vessels the cargo space is divided into tanks.
At the fore end of the hull are the forepeak tanks and at the aft end are afterpeak tanks. They are used for fresh water and fuel. If a ship has double sides the space between the sides contains wing tanks. There is also a double bottom, which is the space between the inner, and outer skins along the bottom of the ship forming double bottom tanks often with cofferdam, the latter is the narrow watertight compartment isolating the space filled with petroleum from the others.
The transverse bulkhead nearest to the stem is called the forepeak bulkhead or collision bulkhead and the one immediately forward of the sternpost is called the afterpeak bulkhead. In addition to upright bulkheads the hull is stiffened horizontally by a number of decks and platforms. The decks run from side to side and all fore-and-aft except some openings. Platforms are partial decks extending only over some part of the length or the breadth. The space between any continuous decks is called a tweendeck.