A while back, roughly 4,000 years or so, the Eskimos developed the first kayak. Kayaking 4,000 years ago was a far cry from what it is today. Made from stitched seal or other sea animal skins stretched over either a wood or whale bone frame, these craft were used to hunt and transfer goods on the inland lakes, rivers and coastal waterways of the Arctic Ocean, and the North Pacific.
Now Eskimo kayak builders weren't just run of the mill builders. They weren't much at swimming, but could flat build boats. Hence, as a side bar, they also invented the Eskimo roll. With the word "kayak" meaning "mans boat" or "hunters boat", each kayak had very specific measurements. The length was typically three times the owners outstretched arms. The width at the cockpit was the width of the owners hips plus two fists. The depth was the fist plus an outstretched thumb. So, with all that being said, the typical kayak 4,000 years ago was about 17 feet long, 20-22 inches wide at the cockpit, and about 7 inches deep. Not much boat to take out on the Arctic Ocean with no life jacket.
Fast forward 4,000 years or so to modern day kayaks. Its almost anything goes. You name it and its being built. Sport, touring, sit in, sit on, modular, paddled, peddled, or sailed. Short or long. All to be had. Very few are used for hunting. And even fewer are used in the Arctic Ocean. Today the kayak is a sport and recreation vehicle with sit in and sit on being the most popular.
An easy activity to get involved in, mistakes can be made when picking out the boat that's right for you. From personal experience sit on with the molded foot stops is the way to go. At about 6 foot tall and 225 pounds, 20-22 inches of cockpit width won't cut it. More of me would be sticking out than would be shoved down into the kayak. The Mrs. on the other hand, she's a sit in with an open cockpit kind of gal. Just something to consider. Weight carrying capacity is another concern. No need to get or rent one that will carry 200 pounds when 225 is what it needs to carry.
Four thousand years ago, the Eskimo got this kayak thing right. With a few modern day revisions not a bad way to spend a few hours row row rowing your boat.