Sealed-hull (unsinkable), these craft swere developed for leisure use as derivatives of surfboards (e.g. paddle or wave skis), or for surf conditions. Variants include planing surf craft, touring kayaks, and sea marathon kayaks. Increasingly, manufacturers build leisure 'sit-on-top' variants of extreme sports craft, typically using polyethylene to ensure strength and affordability, often with a skeg for directional stability. Water that enters the cockpit drains out through scupper holes—tubes that run from the cockpit to the bottom of the hull.
Sit-on-top kayaks come in 1-4 paddler configurations. Sit-on-top kayaks are particularly popular for fishing and SCUBA diving, since participants need to easily enter and exit the water, change seating positions, and access hatches and storage wells. Ordinarily the seat of a sit-on-top is slightly above water level, so the center of gravity for the paddler is higher than in a traditional kayak. To compensate for the higher center of gravity, sit-on-tops are often wider and slower than a traditional kayak of the same length. Although designed to be unsinkable, the "sealed-hull" cannot be completely sealed because differences in temperature would cause the air inside to expand (potentially bursting the hull) or contract. Therefore the kayak may have handle ropes that penetrate the hull and allow some water to enter. Thus, the kayak comes with a drain plug. If the person is heavy enough to cause these "leaks" to be underwater or if the water is rough enough that such leaks are often under the water, the hull may fill with water.