Walker Bay 10 Breeze Tube Kit.
The bright yellow lighter pvc tube. Increases the boats carrying capacity (add 1 adult) and makes it very safe and stable. Works like a stabiliser on a childs bike so if the boat wobbles it rides on the bouyancy tube.
Also works as a splash guard when motoring or sailing and a neat fender when mooring.
Heavy duty version available in thicker pvc, called the RID 310 tube kit.