A tumblehome is a design feature in ships wherein the sides show a convex curvature on the bottom portion and continue up in a slightly concave line on the upper portion of the ship. If the ship were to be cut in a cross section, its shape would resemble that of a pear, with its lower half larger than the upper half. In design terms, the tumblehome is the direct opposite of the flare, which features a more concave curvature that makes for a V-shaped water vessel.
The origin of the tumblehome is somewhat uncertain, but its usage can probably be traced as far back in the 1700s, when many European countries were at war in an attempt to conquer as many foreign lands as possible, along with the notoriety of many pirates. Many warships contained much artillery often located at the upper deck for easy accessibility, thus making the ship top-heavy. Creating a broader and heavier bottom slightly shifts the center of gravity in a lower position, thus making the ship more stable and well-balanced. In the event a ship is hit by cannonballs, the tumblehome design helps deflect the said cannonballs and prevents the vessel from tipping over by the force of the collision.
Another advantage of a tumblehome is that enemy warships are kept as far away as possible, due to the broad distance covered by the ship’s convex sides. Even if the ships stood side by side, there would still be a huge distance between two decks, making it difficult for enemy soldiers and pirates to climb aboard. The convex shape of the ship would also pose some difficulties for invaders to climb up from the waters.
In suitable proportions, the tumblehome proved to be an advantage for stability, but unfortunately, in the 1800s, designs were greatly exaggerated, making the curves too round and too big. This resulted in less stability for the ship, very much like a ball bobbing in and out of the water. Combating strategies and effectiveness were affected as crews were experiencing seasickness, the ship was going off course, and the cannons could not be aimed accurately at enemy ships
In more modern times, the tumblehome feature is applied to small boats and canoes, although it is often combined with other features, such as a V-shaped bottom, to make the canoes slice through the water more easily while still maintaining buoyancy. The design is also applied to US Navy destroyers, as the shape helps decrease radar return and makes the warcraft stealthier. The tumblehome design has even been incorporated in automobiles, as a rounded shape decreases air drag and helps increase speed.