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Many have called this a complete myth
-- choosing instead for clean and smooth.
If someone has definitive proof one is better than the other
we would all like to read the study and analysis.
I'm guessing it's all on the magnitude of 1% plus/minus
since it's low speed human powered watercraft.
Diligently avoid getting nicks, dings, and scratches
in the hull whenever possible to help the kayak/canoe glide
smoothly through the water as you paddle.
Myth ""probably"" originated from :
A micro-grooved adhesive backed plastic film from 3M
was tried out by Greg Barton in the semifinals of the
1986 World Championships in Montreal. Apparently the
grooves need to be very carefully aligned so they are
parallel with the flow of water over the surface.
The size of the grooves was matched to the density
of water and the speed of travel so that the grooves
dampen the turbulence of the water as the flow
detaches from the hull.
This leads up to a popular internet myth :
The crazy idea of hand sanding a "texture" into a hull.
You'll never get the robotic accuracy needed for
perfectly straight and parallel lines down the
entire length of your hull.
Frictional drag comes from the "water on water" inter-action
in the boundary layer, the water that is close to the kayak hull.
The trick is attempting to get smooth laminar
flow with a low "shear stress" of the water molecules
sliding against one another.