RMS Titanic - Construction - Water Ballast

Source: ANATOMY OF THE TITANIC - Tom McCluskie

The bottom hull of Titanic was constructed as a large honeycomb-like structure forming the main water tanks. These water tanks made up the whole of the double bottom and were mainly used for carrying water ballast. Water ballast is of vital importance in ensuring the stability of a vessel at sea. When lightly loaded - for example, with a minimum of fuel, no crew, no passengers and no cargo - a vessel floats extremely high in the water and is inherently unstable.

To counteract this, the bottom of a vessel may be filled up with water to weigh the ship down and increase stability. This is known as water ballast and the amount taken on board will vary according to the voyage requirements - a lightly loaded expecting to encounter stormy weather will take on board additional ballast water to achieve the maximum draught. The deeper a vessel can float, the less susceptible it will be to the effects of wind and sea and the more stability it will have.

In normal conditons, as a vessel is loaded with cargo, stores and/or passengers, the water ballast is gradually pumped until eventually very little, if any, is left in the ballast tanks. With all cargo and other items onboard and ballast removed, the vessel is regarded as being in the loaded condition with the draaught remaining constant to that when only ballast is carried.

The normal service draught for Titanic was 34ft taken at the bow marks and 36ft at the stern. When Titanic left Southamptom to start its voyage across the Atlantic she would have been fully loaded with coal, passengers, crew and their assorted baggage, etc and, therefore, would have had very little water ballast in the double-bottom tanks. As she crossed the Atlantic, the coal fuel would have been quickly consumed by the boilers, and other stores such as food and fresh water would also have been used up. Titanic would, therefore, have become lighter and would consequently have risen in the water reducing her draught.

To compensate for this, and to maintain the optimum draught, water ballast would have been pumped on board to keep the weight of Titanic constant and to maintain stability. It is important to point out that the water ballast in her double bottom at the time of the disaster would have played no part in the sinking, as the iceberg damage occured to the hull above the level of the water ballast tanks.

In parenthesis, it is interesting to note that neither the White Star Line nor Harland & Wolff at any time stated that Titanic was unsinkable. The White Star publicity material issued at the time stated Titanic was practically unsinkable - but the word practically was lost between the release of the publicity material and the subsequent press reports.