Boat Propellor - surface modeling skills?

I have been trying to draw a scale model propellor for a large model
boat. It is a design known as a surface piercing cleaver design and
is found on fast racing outboards.
I can draw it using a swept profile along a helix but I really want
to get an airfoil section to the blade. I normally design machines
and automation equipment so this is a one off. any help would be much
appreciated.

 

MC,

I race an inboard hydroplane (2003 APBA US Nation High Point Champion
!!!) and would be very interested in how you make out with your model.
The surface piercing propellors I use have progressive pitch and I
don't know how they define the cross sections.

I do know there is a company in Washington (??) Herring Propellors
that finishes their props on a multi axis milling machine to make all
the blades identical so the model you are looking for does exist. My
props are cast and then hand finished by a true craftsman, it is
really a black art.

I would love to come up with an accurate model and then have someone
do a STL model for my guy to look at. Seems like there are some
investment casting places that could take the STL model and provide
the raw casting pretty cheaply.

If you get a chance drop me a note ()
and remove _FASTBOAT from the address.

Thanks.

Dan

 

I would have an existing prop digitized with a laser digitizer. Alot of prop
airplane companies use laser digitizers as a quality control check versus
the specs.

 

Thanks Cliff. In fact I'm still looking for a *real* application of
MathSurf, so if you guys have the EQUATIONS of your propeller surface, I'll
do it for you...

 

Sorry for the late reply. I believe what you are trying to do may be
slightly unnecessary. A surface piercing prop provides propulsion by
creating a positive pressure (p.. p.. p.. p.. p..!) on its aft face. This is
in contrast with an ordinary prop that creates a negative pressure on its
forward face (like an aircraft wing) sucking the boat along. The forward
face of a surface piercer spends virtually all of its operating life
ventilated. Therefore an airfoil shape for a surface piercing prop would be
useless for any hydrodynamic purpose. The sectional shape should largely be
driven by structural requirements for the really high loads encountered.

 

Just to mention that our FREE MathSurf and SketchFile macros might help you
a lot.
http://www.dynabits.com/sw/free/macros/sketchfile/index.htm

As I understand from
http://www.aerospaceweb.org/question/airfoils/q0041.shtml ,
modern propellers are obtained by "inverse airfoil design" which gives
NACA-1 or NACA-16 profiles.