I've designed and built kayaks, canoes and paddles for more than half a century. Along the way I've paddled thousands of miles in a lot of different conditions. I've had an on-line presence in the paddling community for nearly 15 years and actively participate in a numerous marathon paddling events. As a result of this I answer a lot of questions about paddling small boats. New paddlers often ask about rudders. This is what I have to say about rudders.
Do you need a rudder on a kayak? The answer is no, maybe, and yes. Let's see if I can clear this up below.
Positive reasons for using a rudder
The number one function of a rudder on any boat I use is to keep the boat running straight. This way I can put all my energy into paddling forward rather than make correction strokes.
To help keep the kayak on track when quartering wind, waves and current. Same basic function as running straight.
To orient the boat at an angle to a certain point when I'm drifting, such as when working a shoreline for fish.
On some specific purpose boats, such as marathon race boats or ocean surf skis, a rudder is designed as an integral part of the design hydrostatics. These boats are difficult to paddle without a rudder. Almost like paddling without a portion of the boat. The primary purpose of the rudder is to keep the boat on track.
Before I list negatives of a rudder I want to point out the most common thought about rudders is that they are to turn the boat. I disagree with this. Sure, a rudder will turn a boat by adding drag on one side or the other which causes the boat to "turn" in that direction. Boats are rear steering, by the way. The rudder drag is the same principal as braking a left or right wheel on a tractor to turn. Braking slows the boat and requires more energy to keep the boat moving. Turn the rudder too far and it will stall and function as a storm sock (or anchor). The turn angle should be limited to 20 degrees. Ten degrees is probably enough.
Negatives of a rudder
Well--if you understand the positives of a rudder the only negatives are added weight, drag, complexity of equipment and the physical effort necessary. Four or five hours into a 100 mile marathon race often leaves one leg or the other totally wasted with the effort required unless the rudder system is set up perfectly.
There you have my basic thoughts on rudders. Unless you have a specific reason, such as drift orientation, a rudder should not be needed on boats under 14 feet. Sixteen feet and above can probably use a rudder effectively. I had an eighteen foot marathon boat that handled quite well without a rudder but was more effective with a rudder because I could put all energy into forward paddling. I have another boat, 20" X 20', that is difficult to paddle without a rudder because that's the way the boat is designed. It's a go very fast boat--and it does.
Gerald is an outdoor sportsman who travels by land or water through mountain forest, rocky foothills, and shifting sand dunes. In his spare time he designs and build kayaks, canoes and paddles. He still competes in select marathon races.