: I think I see your rational for bringing the depth into play. If I
: understand, you are saying that for any rocker value that we compute there
: are infinitely many keel profiles that fit the number, but if we include
: the depth of the keel below some agreed on waterline we get a much better
: idea of the shape of the keel.

that's basically it. in verrrry rough terms, if your example yak was proportionally half as long,and twice as wide for the same load, i think we would say that the keel rocker would be major changed(or would you?). but the figures would be the same.

bow now .75/4 = .188
stern now .5/4 = .125

bow before 1.5/8 = .188
stern before 1/8 = .125

OR
keel before 13.5/16 = .84

keel now 6.75/8 = .84

or the additional bow + stern
both now 1.25/8 = .156
both before 2.5/16 = .156

but if you include the depth, the original rocker is 2.5"/13.5'(or 13.5 x 12 = 162"). percent is 1.54%

the short guy is 2.5"/6.75' etc etc to get 3.08% rocker. which is sorta what the diff would look like from the side.

and any one of us can now draw those 2 exact curves. we know the proportions of the chord length to the depth, . that curve can be overlaid any boat of any length. if we know the depth or the length, we can get the other(whatever we decide it should be 50%(60,70,75)length or 50%(60,70)depth, whatever).
((you know i think it simplest if 50% of the w/l length)
-mick