Tumblehome
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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. It can be seen well in warships of the period of HMS Victory but a small amount is normal in order to allow any small projections at deck level to clear wharves (Pursey p. 218). One of the reasons it was originally used was to make boarding more difficult. It also reduces the beam of the main deck, so reducing its weight and increasing stability. It was abandoned for nearly a century in large warships, as the angle of the hull increased the likelihood of penetration by shells, compared with vertical sides. It has recently been reintroduced for the United States' DDG-1000 class destroyer.
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).
[edit] Modern warship design
Tumblehome has been used in proposals for several modern USN 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 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 United States Navy.
[edit] References
- Mather, Frederic G. The Evolution of Canoeing (1885) [1]
- Pursey, H.J., Merchant Ship Construction Especially Written for the Merchant Navy (1959)
- Vaillancourt, Henri. Traditional Birchbark Canoes Built in the Malecite, Penobscot and Passamaquoddy style
- Modern use For other references, see DD(X) (External links).
