Hi Vance. Phil has nice thrusters, for sure. Looking at all the Kort nozzle
pictures and literature available, there's a lot of differences on the actual
"airfoil" shape of the nozzles. I'm sure there's a lot of highly technical
engineering that goes into designing one of those.
For a home builder, ( with limited computer skills ) I think a simple
airfoil shaped nozzle could be fabricated without too much trouble.
I was thinking that a large PVC coupling, or any type of tube slightly
larger than the prop used could be used as the base. I've been using regular
sheet rock mud over foam to make molds for the various fairings and dive planes,
and it's easy to work with, cheap, and shapes up easily. It sands down very
quickly, and is easy to shape. Then I apply a couple of coats of left over house
paint to "toughen up " the surface.
Spray on some mold release and apply the fiberglass. Lots of sanding and
more layers of fiberglass, a final color coat with UV protector, and it's done.
( sounds simple doesn't it ??? How come it takes so long ? )
Seems like a Kort nozzle could be made the same way.
I bet even just a big thick piece of foam could be carved out to
approximate the whole nozzle piece, and if the fiberglass was thick enough, you
wouldn't even need to remove the foam.
It is pretty simple to "melt" the foam out of the inside with a little
gasoline, but kinda messy.
I see what you mean about the plastic props being light and therefore easy
on the motors. That makes a lot of sense. Maybe an aluminum prop could be made.
I've been playing with the idea of trying the home forge method of aluminum
casting shown on the psub site. Not sure how closely I could get a metal prop to
balance though. Might be fun to try it.
The prop rings I made for the two rear main thrusters were primarily to
keep weeds from getting into the props. The clearance between prop and ring is
about 1/2 inch, and the props are the regular Minnkota "weed wedge" ones.
Probably not the most efficient for a shrouded prop, but I gotta believe
Minnkota spent a fair amount of time designing them for maximum efficiency with
their motors.
The plus is they are cheap ( $36) and easily replaceable, so carrying a
couple of spares won't break the bank.
Frank D.
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