I borrowed H.C. Petersen's "qaanniornermut ilitsersuut" from the public library, which has instructions in SOF kayak building.
In the side views of the kayak, the keel has an area of concavity starting just aft of the cockpit, and ending near the stern. The keel as a whole is quite rockered, except for this area of "un-rocker".
Any ideas what the function of this is?
Owing to the custom nature of kayak building, Petersen purposely is a bit vague on some dimensions, but this concavity looks to be about an inch deep and 5 or 6 feet long. The chine stringer more or less follows the keel line in this area. Petersen states that the drawings and instructions are the result of data collected from many boats and builders, so I do not think that this feature is the result of survey results from any one boat that may have warped.
It the function to alter the stability characteristics? It looks to me like the bottom is quite vee shaped, from the bow almost to the paddlers toes. Perhaps the concavity aft keeps the bottom flatter out to the stern.
Or maybe it increases efficiency somehow? The secret speed banana.