: You don't want the slots any longer or a hard hit on a dock corner
: could crack the rail.

A wood canvas canoe is a good example of spacing, normally the slots and the rib sizes are roughly equal.

That light weight outwale with big gaps can indeed be quite fragile. I've even split softwood outrails on boats where they were epoxied in place to the side of the boat, have one in the back yard that needs this repaired actually.

Bill H.