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1. An inward curvature of a ship's or boat's topsides.
2. A similar curvature of the upper part of the sides of a car or other motor vehicle.

[From tumble, to slope inward (obsolete).]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Nautical Terms) the inward curvature of the upper parts of the sides of a vessel at or near the stern
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
References in periodicals archive ?
New to this category is the Zhaochang patrol ship, purpose-built for long-distance fisheries enforcement with a new tumblehome hull design and a 30 mm gun.
Always a fan of the flared bow and radical tumblehome found on the custom boats of North Carolina he knew exactly what he wanted it to look like.
Pendred Noyce (editor) and Katie Coppens (editor); SEVEN STORIES ABOUT THE MOON; Tumblehome Learning (Fiction: General) 11.95 ISBN: 9781943431335
A vessel with very low displacement, such as the Indeavour, would have its maximum beam well above the waterline and close to deck level, whereas larger vessels with substantial superstructure would keep their maximum beam low at midship and thus would have a more pronounced tumblehome.
Critics say the "tumblehome" hull's sloping shape makes it less stable than conventional hulls, but it contributes to the ship's stealth and the Navy is confident in the design.
Zumwalt-class destroyers have a wave-piercing Tumblehome ship design that provides a wide array of advancements including enhanced stealth and survivability.
[7] Tumblehome: The inward curve of the topsides toward the gunwales, almost always near the stern.
A 'second wave' (completed only after the war had ended) were indeed rather more shapely, with highly exaggerated 'tumblehome', but even these were still essentially floating bricks with bevelled edges!
The leading force in the move from open ocean to littoral thinking is (unsurprisingly) the US Navy, which in 2001 abandoned its projected Zumwalt-class DD-21 destroyer concept in favour of the DD(X), designed to provide advanced land attack capability to assist the ground campaign (see the title picture which shows it firing its 155 mm United Defense Advanced Gun Systems: also note the 'tumblehome' hull form designed to reduced radar response).
Bob Lutz, GM's vice chairman, insisted the roof be lowered one inch, the wind-shield and backlight be given more rake, and the tumblehome increased.
The Kirov-class battlecruisers--with a 22[degrees] "tumblehome" angle imposed on normally vertical bulkheads, screens, and skirts to shield high-RCS components from radar, along with extensive use of radar-absorbent material (RAM)--were remarkably stealthy despite their size.