How to Shape Surfboard Nose and Tail Rocker by Hand while Maintaining a Smooth Curve
Maintaining the curve when increasing rocker is quite simple. Whether using a trim plane or power planer, work the stringer first then shape the foam down to the stringer with the Rasputin tool.
We have developed what is called the "Stair Step Method" to shape rocker and have full control of what you're doing.
The key is to start cutting the stringer close the the nose (or tail) and gradually moving your cut start point back towards the middle of the board and cutting from that point all the way to the nose (or tail). Each cut pass will shave more off the tip of the blank and keep a gradual curve in the rocker.
Mark on the stringer with a pencil how much increase in rocker you want and (say 1/4") on the tip of the nose and start your tool about 3" from the nose and push the cut off the nose, then move back 6" from the tip of the nose and make another cut.... repeat with 3" increments as far back to the midpoint as you'd like rocker to change. Each pass will cut more off the tip of the nose until you achieve the 1/4" total adjustment you've set out for while maintaining a nice flowing curve.
You can stay in the same distance zone (12" from nose in this example) and repeat the steps until you reach the 1/4" nose mark.
If you want a quick flip in the nose then do shorter distance (say 1" increments instead of 3") so the curve is more abrupt.