Avo-

I once built a copy of a commercial kayak - one which my wife owned, so it was nearby for 'consultations'.
:-)

I tried a few methods involving sticks, but it was difficult to replicate the more subtle aspects of the shape - especially as the kayak had a fairly pronounced 'keel' at the stern.

I laminated strips of bending plywood (it's an amazing product which I just discovered in the past 10 yrs or so..) together to make exact copies of the shape at 1 foot intervals. The bending ply is so flexible that masking tape will hold it in place till the wood glue sets.

I made a 'giant caliper' to measure the breadth at each station point, to make sure that the jig shapes were accurately transferred to paper.

I made similar 'jigs' using bending plywood to pick up the bow and stern stem profiles.
Measuring the rocker is critical - that's a job for a stretched string or laser beam and a ruler - at each station.

From the jigs, I produced paper plans on posterboard and cut molds from those.

BTW, I was surprised at how much asymmetry there was in that boat shape - from a 'famous maker' (not Mariner) . It proved to me that boats can have great performance without 'millimeter accuracy' . :-)