William R. Watt ) writes:

I think it should be possible to design a light displacement camping boat
which would plane under both sail and power but I've not come across any in
my recreational reading.

having thought about this some more, from a non-naval architecht's
perspective, sailboats seem to plane more on their bellies while
powerboats plane on their behinds. It probably has something to do with
the location of the source of power, the sail being amidships and the
propellor being well aft. I've never tried working out the math for it.
Another consideration is adding the weight of a motor means the sail has
to plane not only the boat and sailor's weight, but the weigth of the
motor and fuel too. I'd watn it to be a tip up outboard motor so the
propellor could be out of the water and not creating drag for plaining
under sail. Similarly the rudder used in sailing might best be flipped up
our of the water for planing under power. My incomplete SOLO 15 design has
dual rudders so I guess an outboard motor could be hung off the transom
between them. Taking all that into consideration, and allowing for the
tradeoffs, I still imagine it's possible to design a boat which will plane
under both sail and power. Possibly the SOLO 15 boat would as its near
the practical limit of prismatic co-efficient for effecient sail. All the
design numbers for that boat are displayed on my website. If anybody's
interested the plans are not for sale, they're free. But they come with no
guarantees either.

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