With that out of the way, let's consider why fishing kayaks come in such a wide variety of shapes and sizes. It isn't just about ease (or difficulty) of storage, or to match big anglers with large boats, and trimmer casters with slinkier 'yaks. It's chiefly about performance on the intended target water, whether it's the big blue, a vast salt flat, a twisty river or a placid farm pond.
The Bare Basics Of Fishing Kayak Hull Design:
Long slender boats are built to go fast and far. They bridge ocean swells and shrug off waves. The lengthy keel (the center line from bow to stern - think of it as the backbone) holds the boat on a straight course, a characteristic also known as tracking.
Longer kayaks typically have pointed noses that slice efficiently through the water. We're not here to talk hydrodynamics, so take it on faith that a stretched-out waterline translates to a faster top speed. Great for covering distance, 14- to 16-foot fishing kayak such as the ocean-capable Ocean Kayak Trident Ultra 4.7, Malibu X-Factor, or Jackson Kayak Cuda 14 are almost out of place on small water.
Shorter, wider kayaks such as the Wilderness Systems Ride 115 or Malibu Stealth-9 turn on a dime. They have blunter noses that swing left or right at a whim, making them ideal for curvy river channels and backwater mazes. Many have bulbous bows that are designed to pitch easily over small rapids, but labor in sustained up and down chop. These things are slowpokes when it comes to covering distance, but that doesn't matter on a small alpine lake or pond.
Width and Stability
Wider kayaks can carry a heavier load: more gear and more angler. In general, they are more stable. They also take extra effort to move through the water, explaining why Hobie's huge Pro Angler 14 is only practical with a pricey pedal drive. But there's more to stability than meets the inexperienced eye. That's determined by the shape of the hull where the side of the boat meets the bottom, in particular, at what angle the hull is widest. In fancy terms, the chine.
The chine can be a graceful curve (a soft chine) or sharply edged (a hard chine). The chine affects the nature of a kayak's stability, whether it emphasizes primary or secondary stability. Stay with me. Many wider fishing kayaks built with standing in mind or for maximizing carrying capacity have relatively flat bottoms (or tunnel hulls, but that's a topic for another occasion) with hard chines. They feel rock solid on flat water - the hull "locks' in parallel with the water's surface.
Now imagine an angry ocean, with heaving swells and chop. If a kayak featuring tons of primary stability is "locked" in, it's going to feel like a bucking bronco. This is the place for a kayak with a rounded chine which delivers a surplus of secondary stability. It will sit upright in seething water. Paradoxically, although a boat with a rounded side doesn't "feel" as stable on flat water, it's the better choice when the water is rough. The Wilderness Systems Tarpon 160 and Jackson Kayak Cuda 14 is a good example of a fishing kayak with a relatively soft chine.
There's much more to hull design and how it affects on the water performance, but this is plenty for now. If it seems confusing, just remember this: choose longer kayaks for the ocean or large lakes, and shorter boats for creeks and pocket water.