Overview

Decks at different levels in a ship serve various functions; they may be either watertight decks, strength decks, or simply cargo and passenger accommodation decks. Watertight decks are fitted to maintain the integrity of the main watertight hull, and the most important is the freeboard deck which is the uppermost deck having permanent means of closing all openings in the exposed portions of that deck. Although all decks contribute to some extent to the strength of the ship, the most important is that which forms the upper flange of the main hull girder, called the 'strength deck'. Lighter decks which are not watertight may be fitted to provide platforms for passenger accommodation and permit more flexible cargo loading arrangements. In general cargo ships these lighter decks form tweens which provide spaces in which goods may be stowed without their being crushed by a large amount of other cargo stowed above them.

To permit loading and discharging of cargo, openings must be cut in the decks, and these may be closed by non-watertight or watertight hatches. Other openings are required for personal access through the decks; and in way of the machinery space casing openings are provided which allow the removal of machinery items when necessary, and also provide light and air to this space. These openings are protected by houses or superstructures, which are extended to provide accommodation and navigating space. Forward and aft on the uppermost continuous deck a forecastle and often a poop may be provided to...