Peter,

It doesn't seem to matter what the material is, but how smooth it is. If you go back to the bible that Bram Dally used in designing the Swift Solo, (High Performance Sailing, by Frank Bethwaite) the author references a number of sources and standard texts to quantify skin friction. However, he qualifies the results by highlighting that these standard texts are invariably based on straight line fluid flows considering fluid mass, speed and viscosity, and surface roughness, essentially under idealised conditions.

Paraphrasing, by far the best result was on a highly polished chromium plated surface. This was seen as approximating the most highly polished finish practically possible.

His advice is that "at practical yacht or dinghy speeds,... (according to standard texts on fluid dynamics)..., only the bow area of the hull can hope to run with a laminar boundary layer.Under this area, the surface should certainly be highly polished. But beyond this zone the flow will become turbulent and under turbulent flow a highly polished surface will not be any faster than some rougher surface, provided that the roughness is less than some small fraction of the boundary layer thickness."

His real world experiments, based on a variety of experiments and practical observations indicate a different outcome. One of these experiments was that of towing two identical sailing dinghies behind a power boat, one each end of a centrally pivoted beam across the power boat, and measuring towing resistance.

He says "My experience...leads me to believe that as fluid flows curve and accelerate and decelerate around small hulls they can remain laminar for much further than the straight-line measurements suggest. I question whether any surface is 'smooth enough' for a racing dinghy or skiff".

In an allied experiment, (I'm paraphrasing again) he found that the skin friction on a rough rudderblade was about three times that on a wetsanded (to 1200 grit) and buffed equivalent. Significantly, for a high speed skiff like the Swift Solo, he also found that the steering force available from a smooth and buffed rudder blade was about three times that of a rough one - especially within the effective narrow range of angles of attack used at high sailing speeds.

His book makes for some heavy reading, but if you are serious about sailing high speed skiffs like the Solo Swift, then I can't recommend it highly enough. For kayakers, it also contains much of value in observing and predicting wind and wave conditions relative to ambient and water temperatures, wind speed and direction, wind oscillation, distance from shore, nature of shore, cloud formations and a host of other variables.

By the way, if you are building one, I would love to see some construction photos. I'm tossing up whether the next project will be a Cape Ann Storm or a Swift Solo.