We have used, developed, and refined this hatch concept over many years.
It consists of a wooden ring of selected quality ash. Steam bent to shape. Outside there is an edge, also bent and glued together with the ring.
Inside, you mount the inner-"lid". This consists of a tube with a roller closure. It is sewn into the hatch, between the kayak skin and the wooden ring. It assures that the kayak is 100% watertight, even if you lose the hatch cover.
The inner tube of waterproof rip-stop nylon with roller closure is included with every hatch.
Hatch covers in neoprene are sold separately.
Before you mount the hatch, you must drill little holes in the ring, and sand lightly. Then you stitch the tube to the inside of the ring with temporary stitches, cut the kayak fabric and sew the hatch to the kayak fabric.
Size of the different hatches are:
Round: inside diameter 20 cm, outside diameter 22 cm.
Small oval: inside diameter 23x14 cm, outside diameter 25x16 cm.
Medium oval: inside diameter 29x18 cm, outside diameter 31x20 cm.
Large oval: inside diameter 35x24 cm, outside diameter 37x26 cm.