A sponson is a feature on any watercraft that extends from the hull or other part of the vessel to aid in stability while floating, or to act as a securing point for other equipment. Ships and some aircraft commonly feature one or more sponson to help stabilize the craft; vessels with odd body shapes or oddly distributed weight are likely to feature sponsons to help prevent capsizing or other instabilities. On many vessels, these projections from the main body of the vessel can be attached and removed quickly and fairly easily.
On airplanes designed to take off or land in water, a sponson can help extend the hull higher in the water to aid in lift when the plane is taking off. This prevents the plane from sinking too deeply into the water, creating more drag. Helicopters may also feature one or more sponson, and though most helicopters are not designed to land in or take off from water, these safety features are important should the aircraft crash land in water Sponsons on a helicopter can also store fuel or landing gear. When mounted on aircraft, they must be adjusted properly for aerodynamics when the aircraft is in flight; if they are not adjusted properly, the aircraft may become unstable or damage to the aircraft can become possible.
Canoes and kayaks sometimes feature sponson attachments as well for stability in rough waters. These are different from outriggers, which extend a significant distance away from the body of the craft. A sponson will hug in close to the craft, thereby allowing the user to maneuver through tight spaces. Outriggers are usually only used on open waters, and on crafts that are likely to reach higher speeds. If a craft is fitted with sails, it may also feature outriggers on one or both sides to provide stability against the force of the wind. Sponsons are more likely to be used on smaller, slower moving crafts that still require maneuverability through narrow passages.
On land vessels, such as tanks or other military vehicles, a sponson may project from the side of the structure. It is not used for buoyancy in this application; instead, it may be used for armaments such as machine guns, or for purposes of visibility. It can be used for storage as well as a transport platform for people entering or leaving the vehicle.