I guess it comes down to what you want rocker to tell you. Rocker is typically used as a basis for estimating how easily a kayak turns. Imagine two boats with equal rocker by one of my definitions, one boat draws 3 inches, the other draws 4.5 and otherwise everything else is the same. Which one turns more easily?

It is very likely the boat with the least draft turns more easily because it is has a lower lateral plane area. The deeper boat has more area near the ends to slow down the turning. It is true that absolute curvature of the bottom is greater, but is that really what you are interested in? By including the depth in the rocker some people will be under the impression that the boat with more rocker will be more maneuverable when it isn't necessarily.

"Rocker" also plays a part in sea-keeping on waves and ability to surf, but these look at different aspects of the design than maneuverability, so you need to decide what you are interested in first.

This is one of the problems about talking about rocker. Once you are provided a number that everyone can agree on, what do you do with it? Before you decide on a definition, you need to decide what you want to learn from it.

: don't agree
: you would get equal figures as in the other example i chose. but the question
: is do you or mike wish the same figures here?

: but this may because i wish rocker to be the measurement of the curvature of
: the lower portion of the bottom.

: i want draft to give me depth, rocker to give me curvature. my prejudice.

: -mick