[Public-list] Propeller needed

[Bill Ydel]

Does anyone with an Atomic 4 have any experience with the Indigo Electronics
3 blade
 10" x 7.4"   Don Moyer seems to be high on the design.

Bill
SallyB #441

-----Original Message-----
From: public-list-bounces at alberg30.org
[mailto:public-list-bounces at alberg30.org] On Behalf Of Don Campbell
Sent: Monday, March 28, 2005 10:36 AM
To: Alberg 30 Public List -- open to all
Subject: Re: [Public-list] Propeller needed

Joe;
  If you have Excel, and would like a spreadsheet to calculate prop size
contact me
off- list. I have a share-ware version that is fairly accurate. The main
thing to remember is that hull speed is about 10.5 feet per second for an
Alberg 30, and after that props or motor size make very little difference to
speed. If you have a heavy motor that increases wetted surface  area, or
sets the back end into the water, that may slow things a bit. It is a
question of matching the prop to the motor so that the torque, horse power,
RPMs,  and fuel efficiency are maximized for the motor - not the boat. You
need to have the torque, horsepower curves and fuel
efficiency (if available)   for the motor you have in your boat in front of
you to
properly calculate the prop that is the best compromise for your motor. With
a diesel, you really need to be on the torque curve where it starts to
flatten out to avoid lugging  the engine.
    As C.B. has said, motor sailing helps a lot and upwind, will often
increase speed by half a knot and decrease fuel consumption by a
considerable amount.
     Michigan Wheel also have a design they call MP2 which gives a much
greater surface area than the standard prop. We have one on a Canadian boat
and the skipper says it affords much greater boathandling capabilities,
particularly in reverse, than he had with a regular prop.
    There should be a discussion on props in the archives about 13- 16
months ago.
    Rules of thumb,  although some sources may vary a bit:
1" of diameter = 2.5 inches of pitch.
2" of extra pitch will cut RPMs by 450.
Don.
#528

FITZONELOVE at aol.com wrote:

> One question regarding the 13' prop; my aperture is 13.5," which leads  me
to
> believe I can only use a 12" prop to allow the necessary clearance.   Do
> other A 30's have more room?  I'm currently swinging a 12x12, but 
> would  like to go larger, as I have a Yanmar 3GM30, and feel I am
underpropped.
> Thanks,
> Joe  #286 One Love
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