Coming back from the boat today, I experienced one of those instant visons you get once in a while, in this case a vivid picture of a channel across the cabin where the mast would be. A single very live snapshot. That's all I saw. Exciting, huh?
Anyway it was a very heavy epoxy/glass green fairly shallow curved affair with shadows at the ends that makes me think now that they curved down and had some kind of attachment with the interior. My tangible feeling was that it is a drop in. Not done in place. It seemed to be just sitting waiting to be worked in.
Surmise (assuming the image was, shall we say, sent on some legitimate spirit channel) that something was definitely missing. IE the guts in this fiberglass channel. The obvious rest of it. By an extension of the first image it's obvious that the channel is meant to have a wide top put over it that has the same heavy section, probably an even heavier top and a number of 1/4" ribs inside. The whole thing bonded together.