Talked to Dale S. (Flexman) (the mat maker guy) this am. He recently talked w/ GG who told him that the board in CV, as pretty much all the rest of his boards was but a moment in time. He seldom rode the same equipment for more than a few days w/out altering it in some minute way at least (once he got a real feel for what it did in the first place). The one in CV was an early edge board w/OUT runners. He told Dale, once he put runners on one, that was it and if he was still into hard boards he'd have runners on them all. They are only about 1/4 inch deep and about 18 inches long approx straddling the wp and parallel to stringer (one on each rail). They help channel the water back in to concaves and around fin but also act as mini forward fins for holding the high line where the speed is, preventing washing down the face sideways or only being able to take a tight arc at the top of the wave. Instead allowing very high, prolonged trim line. Also, he did vary size of boards and that one may have been too small for him but he said for sure it lacked runners and that was big part of handling prob.what was he riding? In CV I think the problem was the board coupled with the small waves.
GG's surf equipment designs were/are a long arc of change building step by step on previous discoveries, designs, failures, etc. Hard to get a real feel of what he was up to from short vid clip or a few stills. Sure wish I knew!
I'll send it out for you to test at Makaha.