Fascinating Mick, thanks for posting those - Trial and error testing and design is still used today, though much less so with the advent of computers to check designs etc.
Apart from paddlers, another area that fascinates me is hovercraft - I've built four models so far. Sir Christopher Cockerill is often wrongly given the title "The inventor of the hovercraft", in fact he never ever said that he invented it, what he did come up with was the peripheral jet which led to the SRN1, the first succesful commercial hovercraft. And he came up with the idea purely from trial and error testing.
Regards
Eddy