Modern professional ferrocement boatbuilders?

[FAST FRED]

A very well made GRP boat can cheaply be done with a hull weight of 3 lbs /sq ft -35-50 ft or so.

Most ferro boats come in at close to 15lbs /sq ft.

No comparison , but OK for a barge.

 

[Petros]

Petros ... Golf ball dimples in a boat?

Does that actually work without the hull (improbably and unsafely) spinning?

it is not the spinning so much as raising the turbulence on the surface to reduce Cd. It will not work on something the size of a canoe, it only works in a very narrow range of Rn (when you are near transition from laminar to turbulent flow). Something the size of canoe is way past transition which happens in the first 3-6", it only adds drag.

This topic comes up in various forums where drag is a consideration, without understanding how it works you get very wrong results. These are collage students who are not always the most well informed, so either it was a mistake, or done just for fun (or to fool the competition). Most of the modern racing sculls, canoes, etc are professionally designed, and you never see it used there because it does not work when the hull is well past transition.