The Following was posted to the alt.rec.hovercraft group.
Barry Palmer of Sevtec had this to say about the design:
"The propeller design shown will bolt right into the Sevtec
designs, if properly
crafted. Just re-scale it to the diameters in the Sevtec designs. The stock
drive ratios can be used, although there is a possibility that the drive ratios
may have to go up by 5% or so to haul the less efficient wood propeller.
An important addition is that the bore and bolt holes in a wood prop must be
sealed with epoxy for reasonable life, and stainless steel leading edge tape is
a must if operation over bare earth or sand is anticipated.
While the airfoil shape is not real important, the blades must be as nearly
identical as practical. This is for purposes of maintaining aerodynamic
balance (as well as mass balance), which is required for smoothness of
Having said this, I still recommend composite propellers. The propeller and
fan are only a very small percentage of the cost of building a sev, and the
typical builder will eventually spend more on the wood rotors, building,
repairing and replacing, if any real amount of time is put on the skimmer.
I used to build wood rotors for my customers, but after watching one of
Nature's mis-creations eat one right under the yearly fresh coat of Varathane,
and having the 4 year old 84 inch diameter propeller finally unload (that's
engineer talk for blown to smithereens) on a boat dock at close to full power,
I gave up on wood. (No one was hurt, as the runup was done without anyone near
the plane of rotation, and the molded Birch ply rotor disintegrated into mostly
wood chips, throwing no lethal pieces.)
The composite rotors come with three blades, for much smoother operation than
two blades, and as the blades come from molds they are close to identical.
(However, they are not always balanced, so check it!)"
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