Catarafts need to have some sort of A wake is produced off of each tube and they converge in the center of the boat. These wakes cause a hump of water to form between the tubes. As the boat accelerates to speed, the hump moves backward, gets bigger, and it could drown the motor. A 6-ft long plywood or diamond plate aluminum deck, attached to the bottom of the back of the frame, is sufficient planing surface. Also the bottom of the frame should be above mid line on the tubes to be effective. Otherwise this planing surface will act as a water scoop. The transom should have adjustability up and down for different loads. However this planing floor compensates for a wide variation in load if planing speeds can be achieved.
Jag & Leopard Cat Tubes · Lion Series Cat Tubes
This is a solid works drawing of the motorized cataraft we designed for the Alaska Dept of Wildlife. Note that there is a spay skirt, on the front and a spray flap around the down bars on the tube. The tubes are 30 inches in diameter.
NRS Cat Tubes - DRL River Gypsies
This is a picture of the Virus Inflatable Rowing Skull for 2 people. The hardware comes off easily and stores in the trunk along with the deflated tubes. They have been using these types of boats like sea kayaks to island hop in both Maine and in Florida. This boat is 16 feet long, with 13 inch diameter tubes. The difference between these boats and a sea kayak is the amount of gear they can haul, and the stability. This RowCat also comes as single, with 14' tubes, and the same rigging system.
Cat tree - Tubes - Drapaki Rufi