Tumblehome

In ship design 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 (Pursey p. 218).

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 deck 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.

It can be seen well in steel constructed warships of the early 1880's when the United States and most European navies began building steel warships. France was predominately strong in promoting the tumblehome design in their warships, and 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. However, the five follow-on Tumblehome designed sclass|Borodino|battleship|3s, which had been built in Russian yards to "Tsesarevich's" basic design, fought the only decisive steel battleship fleet action in naval history on 27 May 1905 at Tsushima. The fact that three of the four (the fifth battleship, the "Slava" was not completed in time) 'tumblehome' "Borodino" class battleships were lost in this battle, resulted in the discontinuing of the tumblehome design in future warships for nearly all navies.

A degree of tumblehome also facilitates paddling in a canoe or kayak (Mather, 1885), while a greater degree of flare (its opposite) accommodates more cargo (Vaillancourt).

Modern warship design

Tumblehome has been used in proposals for several modern United States Navy ship projects. The hullform also has an exaggerated ram bow; a wave-piercing bow shape, in which the stem rakes aft. This results in a more stable weapons platform, as the vessel does not rise over waves but passes through them. The rake of the stem is continued to the stern in the form of tumblehome. This combination of features results in a lower radar reflection and a very wet deck. This aspect gives the vessel something of the faceted appearance of a stealth aircraft. The ship is a compromise between a surface vessel and a modern-type submarine, which is designed to pass through the surface of the sea rather than over it.

The hull design was to be used on the DD21, but will likely be used on the DDG-1000 ship of the US Navy.

In automobile design

The inward slope of the Greenhouse (automotive term) above the beltline is also called the tumblehome. Less commonly, the inward curve of the body near the bottom may also called a tumblehome. In 21st century autombile designs this "turnunder" is less pronounced or not present in order to reduce aerodynamic drag and also to help keep the lower portions of the vehicle cleaner under wet conditions.

References

*Mather, Frederic G. "The Evolution of Canoeing" (1885) [http://freepages.genealogy.rootsweb.com/~fassitt/canoe_mirror/mather/evo.html]
*Pursey, H.J., "Merchant Ship Construction Especially Written for the Merchant Navy" (1959)
*Vaillancourt, Henri. [http://www.birchbarkcanoe.net/malacitecanoes.htm Traditional Birchbark Canoes Built in the Malecite, Penobscot and Passamaquoddy style]
* [http://www.globalsecurity.org/military/systems/ship/dd-x.htm Modern use] For other references, see DD(X) (External links).
*Borodino class battleship