| On Surface piercing propellers. I think this seems like a naive design for a boat like Planet Solars full displacement circumnavigator. I am sure that the math has been worked out on surface piercing props and is all true. The only boats I see them on are high speed planing boats for example unlimited hydroplanes. It is worth noting that inherently the bottom of the transom is always flush with the water surface on boats like this, and so the immersion of the prop is pretty consistent. It seems to me that the designers for Planet Solar are discounting the effect of waves. Any recreational sailor who has sailed with an outboard on a displacement sailboat knows too well the dilemma of the prop popping out of the water altogether then dunking and cavitating wildly. In any normal seaway the props on the Planet Solar boat will be experiencing a similar effect. This effect will be exacerbated by the fact that the boat is a catamaran and hence pitched and rolled by two hulls spanning the various waves. I am confident that the props would turn in excellent efficiency coefficients in a controlled flat sea or water tank. I am skeptical of how often they will experience these calm conditions on their proposed circumnavigation. Will the dead flat calm days out number the rough ones enough to make it worthwhile. That really is the question. Since they will have excellent weather routing and will be travelling a more or less equatorial route maybe it will pan out. Interesting question, but I kind of doubt it. Hans --- On Tue, 2/15/11, qc_ca_666 <qc_ca_666@yahoo.com> wrote:
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