Fly casting from a sitting position.

Fly casting from a kayak or a bellybaot

Fly casting from a kayak - line slap

Casting a fly from a sitting position is vastly different from casting standing upright, as the body movements are restricted. Furthermore, the elbow movements are restricted in a kayak (or a belly boat), impacting the ability to haul. The seat is lower, and the line will be closer to the water’s surface, making long carries problematic.

Let’s consider the rod – the line – and the casting technique.

THE ROD

Longer rods will get more height, but as they get longer, they become more difficult to use. A 9.5 ft. rod is easier to cast than a 10 ft. rod but has less height advantage, etc. I can’t one-hand a fly rod that’s longer than 11 ft. and it will become difficult to net a fish as the rod gets longer.

THE FLY LINE

You want a weight-forward line. The more weight up front, the better. Remember, the loss of height will limit the carry, and it could become advantageous to use a short head (or shooting taper/head) and/or overline to be able to load the rod with the limited carry.

CASTING TECHNIQUE

The casting is going to have to be “just” arm movements. No way around that one as I see it. So, practice that type of cast from a chair. Sitting on a chair in the grass is VERY helpful, but preferably use a kayak seat or a low beach-style chair. Even a regular chair gives you a false sense of space between your casts and the water and how cramped the elbows are going to be!

Hauling is much more difficult when in a kayak or belly boat. Practicing from a chair is good advice, but that doesn't hinder hauling as much as a kayak will. 

The problem of the water surface proximity will logically be solved by high back casts, paying attention to sending the line over the rod tip. Minimal false casting plus the high back casts will lessen the chances of a line slap behind you, and you must minimize your carry. Now, with these recommendations, you need to shoot the line, and any hauling will be a good addition if there is any room for it.