How much boat? Since we're looking for a sea boat, we can ignore all the whitewater kayaks that look like stubby stealth bombers, and the recreational boats that are basically semi-covered canoes. We're after one of those long, skinny jobs, the longest boats in the store. Sea kayaks range from about fifteen feet to eighteen feet or more. Tandem kayaks - the "two holers" - are even longer, over twenty feet, and rarely a great choice for a first purchase. (Tandems are next to impossible to paddle without a partner and it's easier to share a scenic moment when you're not trying to converse with someone who's five feet behind you.) Still, even a single sea kayak is a lengthy proposition. All other things being equal, a longer boat will make better speed than a shorter one, but unless you're planning an expedition or need to carry a mountain of gear, eighteen feet is a lot of boat to handle - too much for most first-boat paddlers. Sixteen to seventeen feet or so is a good range.
To get our imaginary shopping trip started, we're going to take a random sample of sea kayaks down from their racks and set them on the floor. As you place each boat on the floor, you'll see differences right away. Some will tilt over on their sides while others sit up straight. These flatter-bottomed boats will also feel more stable in the water, especially to the new paddler. They have what designers call initial stability. The ones that are obviously tippy are made that way to make it easier for more experienced paddlers to carve turns and lean into waves coming at them from the side. Initial stability is always high on the list for first-time kayak buyers, but quickly becomes less of a concern as skills develop: A bicycle has no initial stability at all and most of us don't give it a thought.
Walk around your row of boats and look at them end-on. You'll see some are very skinny - no more than an inch or so wider than your hips - while others are a good deal wider. The difference in how these boats perform is pretty much what you'd guess by looking. A narrower kayak will be quicker and more nimble than a boat that's big and wide and, well, more boat-like. If you are interested in the "sport" of sea kayaking and want to carve turns and generally play in the water, the skinnier boat will serve you better, especially as your skills grow. On the other hand, if you simply want to enjoy being on the water, a wider boat may have some pluses for you. A wide boat (over 24") will feel more stable than a narrow one and obviously carry more gear. At Atlantic Kayak Tours, we often put nervous paddlers in our wider boats, but that's not to say that fat boats are for novices. There are a lot of long-time paddlers who simply aren't interested in sports car-like handling. They have other things in mind and like the feeling of having a lot of boat around them.
Now walk around and look at the boats from the side. Some will have long straight keels that stay in contact with the floor for most of their length. Others will have keels that bend up away from the floor, like the rockers under a rocking chair. Which is why this bend is called "rocker". A boat with more rocker will be easier to turn than one with a long straight keel because your turning strokes don't have to twist so much keel through the water. The trade-off is that a long straight keel will "track" better. It will help keep the boat going in a straight line precisely because it is a little harder to turn. Neither quality should be a decision-maker by itself, since going straight and turning are both things you will need to do. And as your skills improve you'll learn how to keep the high-rocker boat on track - or get the good-tracking boat to turn on a dime.
Still looking from the side, study the shape of the whole boat, not just the keel. Some kayak hulls stand up high and proud as a ship, while others have a low deck like a submarine. Boats with a higher profile will have more room to carry stuff, including you, but will be more affected by the wind. High winds are more of a problem for sea kayaks than big waves. And like the difference between a sedan and a minivan, you'll notice a boat's windage most when you're being buffeted by crosswinds.
Most British and "Greenland style" kayaks are designed for windy, exposed conditions so their decks are low to the water. The rear deck of VCP's Anas Acuta is barely two inches above the waterline. It can't carry a lot of gear, but the low profile makes it a joy to paddle on a windy day when others are struggling. Another striking feature of these boats is how the bow and stern rise up to peaks, even though most of the deck is low. The peaked bow and stern help keep the ends from "submarining" under steep waves and add buoyancy that makes the boat easier to Eskimo roll up in case of a capsize.
These boats were designed to handle rough conditions along exposed coastlines.
A different style of kayak evolved in the Pacific Northwest, where there are hundreds upon hundreds of miles of relatively protected waterways. They tend to have high straight decks with lots of room below and long straight keels. These boats are ideal for carrying lots of stuff on long Point A to Point B trips. The trade-off you knew was coming is that with so much boat above the water these kayaks can be hard to handle in windy conditions. Which is why so many of them have rudders.