Garry, they would warp
The reason the ends are pendicular to the horizontal boards is that when the boards get wet on one side, they can warp. I made my replacement teak hatchboards from 1/2 inch solid teak, to replace the teak plywood ones that came with my boat. (Those looked cheap from the day I picked-up my boat at the dealer. My new ones don't have boards on the ends, and I have seen them warp when they got wet and were covered. I have a naugahyde cover on them, and when I added the handle to the sliding hatch, it leaked water on the outer side of the boards, and they warped, until they dried out. I sealed the cover for the handle, so now my boards stay dry and no longer warp. But that's the answer to your question.Aldo