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I am in the process of building an electric
outboard motor. Unfortunatly I am not knowlegable about
props. Does anyone out there have info on how to
calculate the touque required for a given pitch and
diameter of prop. I am an electrical engineer with over 30
yrs expierence in controlling DC motors. I will be
glad to offer any help in this area if someone has
specific question.

Donald,<br>I'm much in the same boat, an EE tryng
to do ME. I have found some help in Douglas Little's
"Electric Boats" book. It's even on Amazon.com if you want
it. It's a little jumbled when he does his
calculations, but if you put various chapters together you can
size the prop and pitch. Unfortunately, Mr. Little
leans to trolling motors as his ultimate driving
unit.<br><br>Also, <a href= target=new></a> has an online form to
size a prop as you need. I'm currently waiting for my
analysis to come back. Seems like helpful people
there.<br><br>There is one place I know of that does manufacture true
electric outboards (as contrasted to trolling motors) as
primary motive units. Ray Electric Outboards. He's at
<a href= target=new></a><br><br>Should you continue, I'd like to know what you do use.
I'm working on an electric inboard design for a small
sailing skiff auxiliary power. Electrically I'm OK, but I
don't even know the words to ask my mechanical
questions.<br><br>Enjoy

Thanks for the feedback. I am quite aware of Rays
Outboards. He's the primary reason why I want to build my
own. I feel that his product is more expensive than it
needs to be and since I want an outboard and he is the
only game in town when it comes to primary propulsion
and not trolling then I am making my own. I am using
a very high effency perminate magnet (servo motor)
with rare earth magnets and a PWM Chopper that I built
my self. I also have a some other ideas which should
increase the overall efficency. If I can get the efficency
over 85%, (Ray says that he is between 70 and 75% eff.
depending on where you read) I should be able to increase
the range (discrarge rate) for a given set of
batteries. A 10% increase in eff. at 3 HP would be about a
10 amp change in the discharge rate. At least it
looks good on paper. I want to thank you for the other
information on the prop web sight and the book. Keep in touch
and let me know how you make out.<br><br>Don

This is for ernie_M_2000<br><br> I have delevoped
two spreed sheet in Excel which provide some help in
motor sizing for selected propelers. Although they only
provide best case scenario they are helpful in playing
what if. They provide a place to start. If you or
anyone else out there would like to have them I will be
glad to share them. They are in excel. They use some
of Dave Gerr calculation form the propeller
handbook. The first on calulates the Bollard Thrust and
RPM's based on the hull configuration (Water line
length, width and hull depth) The second will show the
theoritcal performance of a given propeller (diameter and
Pitch) at various shaft RPM's. If you would like them
you can E Mail me at Donaldbaer@...