Sweep the rectangular end, of the current cutting object, along a curved iso-line curve.

With the rectangle away from the curve, MoI seems to pick the center of the rectangle for the sweep...
So half the height of the rectangle would determine depth of cut...

or place the rectangle at the desired depth w.r.t the isoline curve...(?)

- B

The isolines start angling near the stern and bow, so taking some cross section trims with each plane located where a teak plank ends, might help in forming alternate "isolines" which are parallel. (In parallel planes)

 

(I'll leave it up to the experts now:-)