: Interesting page from Epic:

: http://www.epickayaks.com/news/news/want-rocker-think-again

: Seems to make sense. Comments?

The problem with "rocker' is there is no universally accepted definition of "rocker". Rocker isn't something you can measure. While some people will say a boat has, say "2 inches of rocker" I have no idea how such a measurement is arrived at. If you measure from the entry point at the bow to the deepest part of the boat you are just measuring draft.

What people mean by rocker has something to do with how much of the ends of the keel line rise up. What they are really talking about is "Lateral Plane Coefficient".

The lateral plane is what you see below the waterline when looking at the boat from the side. This coefficient is the area of the lateral plane divided by the LWL times the Draft. In other words it is the ratio of the area of the actual profile shape below the waterline divided by the area an imaginary boat with the same length and draft but a perfectly straight keel line (i.e. one with no rocker at all). A Lateral Plane Coefficient of 1 is no rocker, lower numbers indicate more rocker and 0.5 is a huge amount of rocker.

One reason "full length waterlines" are a good thing in racing is because many races have boat specifications that limit the overall length of the boat. For speed, long waterlines are desired. If you can only have a boat that is 20' long then you want a waterline that is as close to 20' as possible, thus you end up with plumb ends. However, if you look at race designs many of them have relatively low Lateral Plane Coefficents, i.e. even if they have plumb ends, they still have a lot of rocker.