"MBS" wrote in message
om...
I am doing a project that involves using a small electric motor to
power a small boat. Basically, my question involves the propeller
design. I have read that more efficiency can be realized by utilyzing
a lower rpm and a larger propeller. However, a large propeller is out
of the question and the motor that I will be using has continous
torque rating at around 2500 rpm. Therefore, I would appreciate some
expert help with a few questions.
1) In order to stay within efficiency, what is the maximum rpm range
for a small propeller setup using a Kort nozzle? Is the rpm above too
high?
2) When we are talking about efficiency, are we talking about
propeller or overall energy efficiency (I have read that they aren't
the same)?
3) How does blade area relate to efficiency (it seems like the larger,
the less slip)?

1) I don't think so.
2) Propeller efficiency. Normally, you get a torque/hp at the engine,
then start applying losses from transmissions, bearings, U-joints,
etc. to determine how much energy gets to the prop.
3) Larger does mean less slip.

Two places for you to look in more detail: The Propeller Handbook
by Dave Gerr, or Principles of Yacht Design by Larsson and Elliasson.
Both cover the subject in enough detail.