along this line, i really think rocker would be best as a measurment of curvature of a major part of the bottom of a yak/canoe just like a measurement for the curvature of the rockers of a rocking chair, say. but unfortunately traditional thinking/talking is about an inch rise measurment regardless of length of the vessel.

the keel profile vs waterline breaks down with say shorter and shorter vessels having square keel profiles(traditionally all w/ 0 rocker but the #s could radically change)

but say some portion of the waterline length's rise or maybe better of the waterplane area is measured from the lowest part. say the rise at the 1/6 or 1/5 or 1/4 point of the w/l vs the depth or say 1/8 pt of the area vs the 1/2 pt.

(it would be nicer if with respect to the distance in order to get something like the curvature)