Length, Width & Speed
Length and width affect speed and maneuverability. When it comes to speed, it's all about surface area. A long, thin line allows paddlers to slice through the water quickly which is a real advantage if you plan on touring, but a drawback on twisty rivers. A 17 foot-long kayak will go much faster than a 9 foot-long kayak, but a 9 foot-long kayak will turn easier than a 17 foot-long kayak. A narrow kayak is faster than a wide one, but wide kayaks tend to be more stable (depending on hull shape).