Questions about the sport of kayaking. Questions about kayaking in general are better suited for The Great Outdoors SE.
Today there are plenty of different variations of the theme:
- Sit-on-top kayaks are mostly for leisurely recreational use. They have a flat body, usually made of plastic. Holes, so called scuppers, drain incoming water. Kayak rental seem to develop a growing liking of these boats. They are cheap to get be and easy to handle. More sophisticated versions have a chair and straps and recesses to hold equipment and are often seen used by anglers. All other kayaks are sit-ins.
- White water kayaks are short for maneuverability. Their shape supports easy rolling. They are made of very robust plastic materials to withstand strong (ab)use in whitewater and rapids. Inside, they have room only for plastic bags filled with air for improved buoyancy. Primary design goals are safety, agility, speed
- Racing kayaks are lightweight, long, and thin. The small cross sectional shape helps reduce drag while the length improves the aquadynamics. The material is mostly glass fiber or carbon fiber
- Sea Kayaks are long and their shape is cut to provide few working surface for wind and waves. Weight is less a concern than safety, buoyancy (even in cases of damage to parts of the kayak), and ability to carry equipment for multi-day trips. They are the oldest type of kayak and have been in use in their historic forms by several native peoples. In their modern version, they are made out of carbon or glass fibre or durable plastics. They have one to three hatches which are sealed shut agains incoming water for storing up to ~100kg of goods. With proper clothing and sprayskirts only few drops of water enter a sea-kayak.
- Playboats are similar in length to whitewater kayaks, but have a shape that supports even greater agility around all three axes. They are used in free-style competitions to successfully demonstrate predefined figures, the "moves", and combinations thereof.
- "Recreational" kayaks cover the remainder which are in length and shape somewhere between the whitewater kayak and the sea-kayak. While today almost all kayaks are used for recreation the term "recreational kayak" often refers to kayaks not falling in any of the other categories.