Tumblehome

In naval architecture, the tumblehome is the narrowing of a ship's hull with greater distance above the water-line. Expressed more technically, it is present when the beam at the uppermost deck is less than the maximum beam of the vessel.

A small amount of tumblehome is normal in many designs in order to allow any small projections at deck level to clear wharves.

Tumblehome was common on wooden warships for centuries. In the era of oared combat ships it was quite common, placing the oar ports as far abeam as possible. This also made it more difficult to board by force, as the ships would come to contact at their widest points, with the decks some distance apart. The narrowing of the hull above this point made the boat more stable by lowering the weight above the waterline, which is one of the reasons it remained common during the age of cannon-armed ships. In addition, the sloping sides of a ship with an extreme tumblehome (45 degrees or more) increased the effective thickness of the hull versus flat horizontal trajectory gunfire (a straight line through faced more material to penetrate) and increased the likelihood of a shell striking the hull being deflected—much the same reasons that later tank armor was sloped.

It can be seen as well in steel constructed warships of the early 1880s when the United States and most European navies began building steel warships. France was predominantly strong in promoting the tumblehome design in their warships, advocating tumblehome to reduce the weight of the upper deck, as well as making the vessel more seaworthy and creating greater freeboard. France sold their newly constructed pre-dreadnought battleship Tsesarevich to the Russian Imperial Navy in time for it to fight as Admiral Wilgelm Vitgeft's flagship at the Battle of the Yellow Sea on 10 August 1904. The Russo-Japanese War proved that the tumblehome battleship design was excellent for long distance navigation, especially when encountering narrow canals, and other waterways; but that it could be dangerously unstable when watertight integrity was breached. Four tumblehome Borodino-class battleships, which had been built in Russian yards to Tsesarevich's basic design, fought on 27 May 1905 at Tsushima. The fact that three of the four were lost in this battle resulted in the discontinuing of the tumblehome design in future warships for nearly all navies.

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