>An "ogiveal" shape is optimized for rapid
>transit thru a fluid medium.. That's why the nose of a large (subsonic)
>aircraft , or sub,..is shaped similarly to that of a bomb...or raindrop.
When my uncle built a series of windmill-powered yachts, he did quite a bit of research into efficient blades: it was fascinating. The best shape turned out to be a stretched out egg: big fat radius at the hub feathering out to a thin tip on this 12m diameter propellor. Then under the water things changed again, dropping down into this very different set of Reynold's numbers. You should have seen the kevlar-sail racing set when we drove up the harbour straight into the wind ;-)