oldmansurfer wrote:I think tail rocker essentially shortens the board as far as the wave is concerned. So the push you get from the board is less than that of a board without tail rocker. I think this is only in a down the line aspect. But the wave is pushing on the bottom of the board steadily till it gets to the tail rocker then suddenly that surface drops away and the board has less push. This would be at planing speed so essentially the rocker part of the tail comes off the wave a bit and less force is applied to that area occupied by the rocker. Speed is created by the wave pushing on the board (except for turning up and down the wave ie speed turns)and once you are planing the more board surface pushing the faster you go. Now this is completely obliterated by the speed that can be generated by turning rapidly on a steep wave which is why longboard don't do as well on steep fast waves.. I think there are however situations where you get the board in the right place and rocker helps it to fit that place and makes it go faster but those situations aren't the majority of the wave at least for us kooks

(unless you are riding straight in)
I think my understanding of a wave's "push" is a little different from yours. It's always complicated with me

Sometimes when I'm out surfing an unbroken wave will approach me and I'll just sit on my board motionless. I've sat there plenty of times as the wave breaks about six inches behind me. I've never been pushed forward by an unbroken wave. I bob up and down. The only time I feel like I'm "pushed" is when the lip of the wave throws out. If I'm up at the lip and stay there, the wave's lip will throw me forward too. If I'm under the lip in the midsection of the wave, there's a good chance I'll just bob up and down as the wave breaks over me and I'll pop out the back. Water is sticky, however, so if the wave starts plunging, then I might stick to the water at the top of the wave and get sucked over the falls. My point is that I think it's important to get rid of the notion that a wave is pushing stuff forward. A wave, in my mind, is essentially a moving, watery ski slope. That slope is moving forward and the water it comes up against just sloshes up and down as the cylinder of energy passes through that area of water.
Besides the plunging lip I also feel a push from white water. It's important for me to remember, though, that white water is not being pushed by the wave. The white water is cascading down the slope of the wave. This is easier to see when you watch the huge waves at Nazare. Watch how the white water rolls down the slope of the wave. As far as I can tell, the whitewater isn't being pushed; it's falling down the face of the wave face.
Anyway, there is a "push" that is important with regard to a wave. That's the push a surfer makes when they weight their board by moving around on it. In other words, the way a surfer pushes down on their board with their body will generate speed, It works the same way on a ski slope, ramp, or any incline. How does this apply to surface area? I suspect that the more a surfer puts pressure on the deck of their board, the more speed they will generate. If their board isn't in contact with the water (more tail rocker), then that push on the board from the surfer will not convert to board speed. I think that's what's going on

Sometimes I have to write about this stuff to clarify it in my own mind, but I have no idea if I'm right or not. So take what I say with a grain of salt.