A sunny summer day on a small lake or pond just cries out for a small boat. A recreational kayak can be just the thing. Intended to be small and easy to handle, not requiring much skill, comfortable and stable, recreational kayaks provide the ideal craft for poking around, watching wildlife, or just floating care-free on a mirror smooth pond.
Recreational kayaks tend to be short because a short waterline helps make the boat more maneuverable which is nice for poking into little coves and streams. Short boat are also easier to transport - they may even fit on the back of a pickup truck - and can be made lighter weight than longer kayaks. These boats tend to be relatively wide. This is in part due to the fact that since they are short, they need extra width to give them buoyancy. However, wider boat tend to be more stable, and the added width helps give more room for comfortable seating.
The trade-off with a short, wide boat is they are not generally as "sea-worthy" as longer narrower boats. If you get caught out in rough conditions you may find a recreational kayak hard to handle and get back to shore safely. They generally are not equipped with the safety features of other kayaks.
While sea kayaks were originally designed for use on the ocean, they are at home on any large body of water or in situations where you want move efficiently for a long distance. Sea kayaks are the nearest ancestor of the original kayaks created by the Inuit and Aleut peoples of the Arctic. These original kayaks were often quite narrow and fairly long. This help them move efficiently through the water even when the wind blows and the waves get large. This makes them well suited for any body of water where the conditions may get rough or if you just want to be able to go a long distance with a minimum of effort.
Sea kayaks are typically designed with a cockpit small enough to accept a spray skirt. This helps keep water out of the cockpit. They also often are equipped with bulkheads that provide additional safety and a dry place for storing lunch or camping gear.
Due to their length sea kayaks are typically heavier than recreational kayak. The length also makes them less maneuverable for investigating small coves and streams. They will not be as responsive as a whitewater boat when attempting to navigate fast moving water.
Traditionally kayaks were solo boats, but a tandem or double kayak is a great way for two paddlers to get out on the water together. Working together in one boat two people can typically go faster than each would go alone. This especially useful if one paddler is less experienced or not as strong a paddler. Instead of being left behind by the stronger paddler, they both end up going faster.
Multi person kayaks can either have one large cockpit or a separate cockpit for each paddler. A single large cockpit can be handy if you want to paddle the boat solo as it lets you position yourself in the middle to balance the boat. The separate cockpits allow the use of individual sprayskirts and generally just do a better job of keeping water out of the boat.
Tandems or kayaks designed for more than one paddler tend to be longer and wider than solo boats. This accommodates the need to carry more weight. The added width also provides more stability which is nice when two individuals are each doing their own thing.
The distance between the seats will effect how easy the boat is to paddle. With the seats close together, if one paddler stops paddling the other may end up whacking into their paddle. Increasing the distance will minimize this problem. This lets each paddler move at their own rate. However, it should be noted that the boat will move a lot easier if everyone paddles in sync with each other.
There are a lot of different kinds of racing kayaks, but almost all have the characteristic of being fast. There are several things that contribute to speed. You will often here about "hull speed" in relation to boat speed. This term is a misnomer in that it implies that there is a speed a hull will go. What it really indicates is the speed at which the hull starts to become rapidly more inefficient.
What hull speed suggests is that longer boats can go faster than shorter boats. This does not mean that they are automatically faster, just that a longer boat starts losing efficiency at a higher speed than a short boat.
The other big factor in speed is "wetted surface area" or how much surface area is in the water. This is important because as you move through the water the water must slide across the surface of the boat. The more surface there is to slide against, the more friction there will be and the slower the boat will go.
The easiest way to reduce the wetted surface area is to make the boat narrower. As a result, there are two primary options for making a racing boat fast: make it long and make it narrow. Therefore, most racing kayaks you see will be as long and narrow as they can get away with. There are typically constraints on these factors. For example, if you make a boat too narrow, it can be so unstable as to be impossible to keep upright. The other big constraint is racing rules.
Most race organizers will set maximum lengths and minimum widths in an effort keep to their events as fair as possible. Their goal is to make the race a test between individual paddlers, not a test of the fastest boat. However, it is the kayak designer's task to try to develop the fastest boat permitted within the rules.
This battle between race organizers and boat designers can create some funny looking boats, but the most common solution creates a boat with a plumb bow and stern. In this way, the boat can get as long a waterline as possible within the prescribed overall length. You will also often see a fair amount of "flare" in the cross sectional shape of the boat. This permits a narrow waterline beam with a wider overall beam that meets the rule specifications.
Neither of the these solution necessarily result in the best boat possible for the purpose if there were no design constraints imposed, but they can make the boat quite fast within those constraints.
The other consideration in a racing boat is stroke mechanics. Despite kayak designers best efforts to make a fast boat, in the end there are really only fast motors. In order to go fast, the person paddling a kayak needs to be strong and have good technique. The design of the boat will often include features that help the motor maintain a good and strong paddle stroke.
The boat should not get in the way of the stroke, and the cockpit should let the paddler move as needed to paddle with full power. This often means the boat is quite narrower in front of the cockpit for a clean start of the stroke. The cockpit may be long to permit the paddlers legs to move.