What is an Outrigger?
Outriggers are basically training wheels for kayaks. They consist of a beam with a pontoon at one end and an attachment point to the kayak on the other. The beam also can be made longer and a pontoon attached to both ends. The center of the beam can then be attached to the kayak to provide additional stability.
The pontoon can be made of many different materials. Ideally, choose a material with a low weight-to-volume ratio. Thin-walled PVC pipe is a common solution. Building a small skin-on-frame pontoon is an option as well. The choice of building materials and methods depends on the time and effort you wish to spend on the project. The strength-to-weight ratio of the outrigger's beams should be as high as possible. The beams should be rigid enough not to bend while preventing roll, and light enough not to add appreciably to the overall weight of the kayak. Galvanized electrical conduit can be used for smaller outriggers. It is easily bent into gentle curves for proper placement and has enough rigidity to support moderate amounts of stress. For larger jobs, laminated wood frames are a better option.
Placement of the support beams for the outrigger is critical. Beams should be attached to the deck of the kayak far enough from the cockpit to not interfere with paddling. The beams also should be long enough to prevent the pontoon from becoming an obstruction to the paddle.
If you chose to build your outrigger with 6-inch diameter, thin-walled PVC drainpipe, you can calculate the buoyancy with the following formula: volume = 3.1415 x the radius squared x the length. For a 72-inch section of pipe, the calculation would look like this: 3.1415 x 9 x 72 = 2,035.692. This is the volume of the pipe in cubic inches. Convert this to cubic feet by dividing volume by 1,728. Thus 2,035.692/1,728 = 1.178. This is the amount of water the pontoon will potentially displace. Since the weight of fresh water is roughly 62 lbs. per cubic foot, this pontoon will have a buoyancy of 62 x 1.178 or slightly more than 73 lbs. Within reason, the further from the center line of the kayak this is placed, the more stability will be achieved. Using the calculation torque = force x distance, 73 lbs. of buoyancy placed 3 feet from the center line of the kayak will exert 219 lbs. of resistance to rollover in the cockpit.
Outriggers will add drag to your kayak. You will want to make them as hydrodynamic as possible. Consider this when designing and choosing your material. A slick finish and tapered ends will minimize the increased drag.