[Alberg30] Prop pitch

[Don Campbell]

For Bill Blevins;
    I have just done some research on prop pitch for both A22 and A30
models and it is surprising how far out we have things on most boats. I
used the resources of Michigan Wheel (and others) and they use a couple
of things most of us forget, the first of which is that there should be
15% of the diameter of the prop slot left open. Thus the max prop they
suggest for an A30 is 10" diameter. The pitch depends on the motor
characteristics but for the Atomic 4 gas it was a 10 - 5   3 blade
sailer.
    Janski has done considerable with MB as well,  for Viva II and he
has purchased a MP-2  13 - 6   2 blade from Michigan Bronze to replace
the original 13 - 7 Columbia prop. There is about twice the surface area
on the blades of the MP-2 as on the Columbia. Unfortunately, he was
unable to get Viva II into the water last year to try this prop but has
plans to get her going this year  if we ever get rid of winter up here
in Canada.
    I have managed to find an Excel (TM) prop calculator thanks to Jose
Campione in Ottawa at (http://www.yosc.ukgateway.net/propcalc.xls) which
you might enjoy because you can simulate various situations without
having to go onto the water,  and get results for  for 2, 3 and 4 blade
props. This programme has a 55.94% slip built in to every calculation,
but also shows the theoretical pitch calculated before slippage is
considered.. I used increased displacement to simulate increased waves
and headwind.
    The other rules of thumb that most use for props are that 1" of
pitch = 200 rpm on the motor and 1" of prop diameter = 2.5" of pitch.
Motor performance is key to getting the correct prop.
    Net result:  Props are a compromise just like the rest of the boat.
Don Campbell, White Opal # 526

 +---------------------------------------------------------------+
 |                This Old Boat by Don Casey                     |
 | http://www.amazon.com/exec/obidos/ASIN/0071579931/alberg30-20 |
 +---------------------------------------------------------------+

Public-list mailing list -- Public-list at alberg30.org
http://www.alberg30.org/mailman/listinfo/public-list
To unsubscribe: email to Public-list-request at alberg30.org
Include command "unsubscribe <password>" in subject or body.
Use command "help" for more options.

 1049817782.0