This is a great article about buying a kayak and their speed.

Generally, the longer and narrower a kayak the faster it is. There is a trade off with our next characteristic. If a kayak is long its not going to turn as easily as a shorter kayak. If the majority of your fishing is close to shore or in small, protected areas, then sacrificing maneuverability for speed isn’t the way to go. However if you’re fishing a big reservoir, bay, sound or offshore the ability to cover distance may be very important. The faster kayaks, used for fishing, are generally known as touring style kayaks.
Speed is only important if you need it however it’s misunderstood. Beginners often say that they don’t need to be the fastest kayak out there and will gladly sacrifice speed for stability. What they don’t consider are the limiting factors involved in kayaking. A kayak is a non-motorized craft. You are the engine so you can’t think of it as a car or similar vehicle. A kayak has limitations as to how fast it can go. Part of it is its design and the rest is dependent upon its power source with that source being you. Some kayaks have a top speed of only a few miles per hour while there are others that are much faster. There are also a couple of types of speed - top speed and cruising speed. Top speed is how fast the kayak can travel when maximum effort is applied. It’s similar to the top speed of your vehicle. It doesn’t serve much of a purpose, as you can’t drive that fast most of the time. Your body is the kayaks engine and you can’t paddle that hard for very long. Cruising speed is the important speed. It’s the speed at which you can comfortably propel the kayak. Cruising speed will vary as it depends upon your conditioning and your kayak. Your cruising speed will most likely increase as your conditioning improves with regular paddling, and as you become a better paddler. Then it’ll become a relative constant that’s affected by other factors like wind and current.

Here’s how it works. Let’s say that the place you plan on fishing is 1 mile from where you’ve launched your kayak. Kayak ‘A’ is shorter and wider and kayak ‘B’ is longer and narrower. ‘A’ cruises at 2.5 mph and ‘B’ at 4 mph. So ‘A’ is going to take 24 minutes to cover the mile while ‘B’ is going to take 15 minutes. That’s a difference of 9 minutes! Should the distance turn out to be 2 miles then its 18 minutes. This is a simple example and doesn’t add other variables that will most likely exist like current, wind and waves/chop. All of these will affect the movement of the kayak over the water and its cruising speed. The less efficient hull of ‘A’ will be more greatly affected by these additional factors than the hull of ‘B’. This means that the actual difference it takes each kayak to cover the mile could be considerably greater then the 9 minutes and would probably end up being closer to twice as long. The longer narrower kayak ‘B’ is going to handle these variables much better as its hull was designed to handle more varied conditions.

Here’s a real life example that adds in the variable of wind and waves. Three people on a trip we took in June 2004 to Cape Cod decided to fish Barnstable Harbor one day. While on the water the wind increased out of the south to over 25 mph. This happened to be the direction that they had to paddle to return to the launch point. Two of the guys had kayaks that were capable of a top speed of over 5 mph however they weren’t efficient touring style hulls. Under good conditions they could cruise easily at 3.5 mph. They had wide flat bottoms and a hull configuration that lacked another feature called rocker. The design was best for calm water. The third kayak was a pedal drive system that had a similar top speed. Even though the pedal craft wasn’t faster it was a completely different design. Its design made it function similarly to a more efficient touring style hull. The 2 conventional kayaks could barely make any headway against the strong wind and seas because their design couldn’t perform properly in the choppy water. Rather then slicing through the chop in an efficient manner they went over the tops. They caught more wind and while paddling forward the kayak was also being pushed backwards. So a lot of the energy they expended wasn’t being translated into forward progress. Because of this they were only able to sustain about 1 mph while the pedal kayak could travel much closer to its normal cruising speed. The pedal yak ended up towing the other 2 kayaks back to the launch. In fact the less efficient a hull the more the variables of wind, current and waves will rob the craft of forward progress.

Speed is more than how fast a kayak can travel. It’s a function of efficiency over the water. The propulsion is limited by how much you can paddle and is dependent upon your physical ability and the amount of energy you have. Both of these are finite. We’ve found that many people who end up purchasing a less efficient, slower kayak end up getting a more efficient one if they are in a locale where these variables exist. That turns out to be a lot of places.

http://www.kayakfishingstuff.com/dru...nt/kayak-speed