Sounds like a question to ask on the WoodenBoat website: http://www.woodenboat.com/
They''ll proabably have six different types of clam plans available, depending on which Ocean you want to sail in, and the kind of clams that grow there.
Eric, am I right in thinking you mean a traditional skylight? They require a pretty high level of joinery-skill to build properly, and even then most seem to leak. But they certainly look nice.
I came across an article in an old WoodenBoat a while back that gave details of a fake skylight that was really a Dorade-type ventilator. You might perhaps like to consider that instead. I''ve posted a self-explanatory sketch at --