Why concave in the tail when it already has flip?

I’m of the understanding that concave in the tail is to streighten out the rocker to give it drive. When looking at a board from the side, with the bottom side down ,the tail flips up. Why put concave in the tail if its higher than the mid section anyway? Won’t this cause more curvy rocker? Would’nt a single concave in the middle and none in the tail streighten out the rocker?

Think about how a board planes on the water. your basically standing on the rear half and the concave creates a straighter line through the center rocker while keeping the curve on the rails.

Mike: If the concave was the same depth in the tail as in the middle then your observation would be correct as to the concave rocker being lower but not straighter. On many boards the concave starts to become shallower or fade out as it moves towards the tail giving the board a bit of hook. Where it fades out completely seems to depend on the shapers view of a good blend. On other boards the concaves or channels are carried right off the tail. In this case I think the shaper has decided that breaking up the flow adhesion into areas will increase speed more than a straighter rocker. It seems some shapers are trying to gain better performance by looking closer at the rocker while others are looking closer at the bottem surface. The best board, of course, will be the best blend for the individual rider. I suspect this is one of those questions engineers would answer with technical terms and shapers with emotive or practical vocabulary. I suppose the best answer like the best board is all in the blend. Patrick