SIK (Sit In Kayak) vs SOT (Sit On Top)
A sit in, or sit inside kayak(SIK), is a traditional kayak configuration where the kayaker sits inside the kayak hull. The kayaker sits low in the kayak, which makes it more stable. This is the type of kayak used for white water kayaking. The main drawback with this type of kayak is that it can fill up with water if capsized making re-entry difficult and potentially dangerous. Sit on top(SOT) kayaks are, by far, the most popular kayak design for fishing. There are many different paddle and pedal SOT configurations and personal modifications. Sitting on top of a sealed hull, if the kayak should capsize, flip it over and climb back on.
Length and Width
Generally speaking, longer means faster and wider is more stable. Most fishing kayaks are a compromise between the two. The "bigger" the water, the longer the kayak. 10'(3.05m) kayaks are OK for small lakes and mellow conditions, but if you're headed out on the ocean or large body of water, especially if there is wind, you should be looking in the 12-14'(3.66-4.27m) range.
Fishing kayaks have have a weight capacity. This is the weight a kayak can carry and still float. The weight includes the kayaker and everything else on the kayak. If you are a bigger person, or carry a lot of gear, you may need a longer and/or wider kayak. If you are near, or at the kayak weight capacity, the kayak's handling is probably going to suffer.
Paddle or Pedal?
Until Hobie came out with their popular Mirage Drive pedal kayaks, this was not a question that needed to be asked. Now, there are several kayak manufacturers that have leg driven propulsion systems in addition to the traditional paddle driven kayaks.
The traditional setup where the kayak is moved through the water by a paddle with a blade on each end. Paddle kayaks are at the lower end of the fishing kayak price spectrum. Expect to spend $350-$1000USD for a sit on top(SOT) paddle fishing kayak. Most novice kayak fishermen will start with a lower priced SOT paddle kayak, experienced fishermen will likely end up at the higher end.
Paddle kayaks are the lightest fishing kayaks. A top line paddle fishing kayak will probably be about 60-70 lb(27.22-31.75 kg). If you have to carry your kayak to the launch or lift it up on the top of your vehicle, this is an important consideration.
Without a drive system, there is more below deck storage. This is important if you fish in wet weather or go through breaking surf. With scuppers in place, a paddle kayak can be completely dry.
The draft of a paddle kayak is only a few inches so it can navigate very shallow water and glide over seaweeds. An experienced kayaker can quickly maneuver the kayak in very close quarters in all directions.
Pedal driven kayaks have become very popular and the drive systems get better all the time. These kayaks are great for "hands free" fishing and long trolling sessions. You have to control the rudder with your hands, but your legs do most of the work. Pedal kayaks are fast, fit pedallers can cover lots of water.
Pedal kayaks are more expensive and generally heavier than paddle kayaks. Expect to shell out $1000-$4000 for a pedal driven kayak. The largest of the pedal kayaks can weigh well over 100 lbs(45.36 kg) and would be difficult for one person to lift on to the roof rack of a car, truck or SUV.
The pedal drive systems have moving parts. Some have cables and/or chains. Rudders, which are required to steer pedal kayaks, have moving parts and cables. These parts require adjustment, maintenance and replacement due to wear. The pedal drive can fail at inopportune times.
Pedal drives stick out below the kayak. The drives should be stowed for beach launches and landings to avoid damage. Care must be taken not to damage the drive in shallow water, or water with submerged obstacles. Seaweed and fishing line can get tangled in the drive.
The pedal drive passes through the hull and allows water in the kayak. Seats are higher to avoid sitting in water, this raises the center of gravity. The drive placement reduces dry storage below deck.
The largest of the current models of pedal driven fishing kayaks are more like boats than kayaks. 150 lbs(68 kg) and wide enough to easily stand and fish. Many of these kayak owners have trailers to transport the kayak and a cart to get it to the water. You can carry a lighter kayak and launch anywhere you can get to the water. A larger pedal kayak/boat will mostly be limited to boat launch ramps, beach or mellow launch area.
Some kayaks can be fitted with electric motors. These watercraft blur the lines between "kayak" and "boat". These boats are very heavy and most likely would have to be transported on a trailer. In many states, any watercraft with a motor would need to be registered. If you are unable to manage a paddle or pedal kayak, a motorized kayak would be an option.
Some kayaks have an option to use a sail. Sailing is fun, but a kayak is not a sailboat. Kayak sails are options on kayaks that have reinforced mounting for the sail's mast. A sailing kayak may also require the use of outriggers, also called "amas", to stabilize the kayak. The hull shape and lack of keel or centerboard will limit kayak sailing to moderate winds.
When you have an idea of what kayak you might want, do a little research on the internet to check all the details. If at all possible, visit a dealer to check out the kayak you're interested in and take one out for a demo. It's worth driving a little to get the kayak you want.