[Public-List] Best prop?

Kris Coward kris at melon.org
Wed Jun 19 19:05:39 PDT 2024 

15% of 14" is 2.1", so subtracting that from 14" leaves 11.9" as a maximum diameter for a prop in that aperture to avoid cavitation. I'd probably just stick a 12" prop in a 14" aperture, and if I were to notice any indications of cavitation, see if I could just grind out the extra 1/8" of aperture height that 15% rule calls for (but I'm guessing that there was rounding to get the 15% figure and it's in the right direction to allow rounding 11.9" to 12" without incident).

Cheers,
Kris


-- 
Kris Coward
https://unripe.melon.org/


On Wednesday, June 19th, 2024 at 17:00, John Johnston via Public-List <public-list at lists.alberg30.org> wrote:

> Thanks to all replies - I previously had a 12x10X3, which worked pretty well, but I had to limit the throw ( I have pedestal wheel steering) by clamping stops on to the cable as full hard over it would clip the rudder. My reason for exploring other options is that through researching propeller size determination I repeatedly came across the formula that the prop needs to be at least 15% smaller than the aperture to prevent cavitation and interrupted flow of water, which, the aperture having a vertical height of 14”, if my math is correct, would result in a 10” diameter prop- a radical reduction.
> However, I regularly read the public list and recognize all the responders as being seasoned and well informed, so perhaps 12x 10 is once again the way I go.
> If anyone has reasons for me to do otherwise please reply.
> And thanks to those that did. You are a great resource.
> 
> 
> And if my original post is not available I have a Westerbeke 20 2b with a 2.47:1 JS transmission.
> 
> John Johnston #69
> Sent from my iPad
> 
> > On Jun 19, 2024, at 10:37 AM, Mike Lehman via Public-List public-list at lists.alberg30.org wrote:
> > 
> > I have a 3 blade 12 diameter 10 pitch 7/8 shaft on our A30 with a
> > Universal 30 hp 4 cylinder. People comment that I could pull water skiers.
> > The reason for 12" is to reduce prop wash and noiseon the hull.
> > 
> > > On Wed, Jun 19, 2024, 9:57 AM Pier-Andre Bouchard St-Amant via Public-List <
> > > public-list at lists.alberg30.org> wrote:
> > > 
> > > I understand. I would not have undertaken such task if Jean-du-Sud already
> > > had an aperture.
> > > 
> > > You can however reduce the featherstream size to fit a standard apterture.
> > > Which size is best, then, is a question for someone else.
> > > 
> > > Fair winds!
> > > 
> > > Pier, #399.
> > > 
> > > --
> > > Pr Pier-André Bouchard St-Amant
> > > 
> > > Bur.: +1-514-849-3989 #3923
> > > Cell.: +1-514-424-6632
> > > pabsta.qc.ca http://pabsta.qc.ca/
> > > 
> > > > Le 19 juin 2024 à 09:38, John Johnston via Public-List <
> > > > public-list at lists.alberg30.org> a écrit :
> > > > 
> > > > Thanks, Pier for the prompt and very informative reply. Changing the
> > > > aperture size to accommodate a larger prop is an interesting approach, and
> > > > perhaps one I will pursue in the future while hauled out. What I am seeking
> > > > right now is an off the shelf prop that will work best within existing
> > > > limitations of the aperture. I don’t want to miss another Summer not
> > > > sailing, and I don’t have the time ( nor the heart) to do more than a quick
> > > > haulout and install.
> > > > 
> > > > All the best,John
> > > > Sent from my iPad
> > > > 
> > > > > On Jun 19, 2024, at 8:51 AM, Pier-André Bouchard St-Amant via
> > > > > Public-List public-list at lists.alberg30.org wrote:
> > > > > 
> > > > > Hi John,
> > > > > I used a 13" featherstream 3 props on Jean-du-Sud. Here for the model:
> > > > > 
> > > > > https://www.darglow.co.uk/featherstream/
> > > > > 
> > > > > Here for the original calculations:
> > > > > https://en.jeandusud.com/repowering-an-alberg-30-part-1/
> > > > > 
> > > > > The biggest downside of this model is the price. The upside is reduced
> > > > > drag.
> > > > > 
> > > > > Upon purchase, they will adjust the blades' angle to the most efficient
> > > > > angle at peak power. You can adjust the angle at a later time, or ask them
> > > > > for an angle specific to your calculations (peak power at low rpm, etc)
> > > > > 
> > > > > I would pay attention to the propeller size and the rudder max
> > > > > availlabe size while in a full turn (on both sides). That is also an
> > > > > implicit limit on the propeller size.
> > > > > 
> > > > > Best,
> > > > > 
> > > > > Pier, #399
> > > > > 
> > > > > Le 19 juin 2024 08 h 36 min 09 s HAE, John Johnston via Public-List <
> > > > > public-list at lists.alberg30.org> a écrit :
> > > > > 
> > > > > > Hello folks, especially those Alberg owners who have diesel engines -
> > > > > > Can you recommend a 3 blade prop that is suitable for the aperture
> > > > > > limitations? The 14” height calls for a smaller prop to be effective-
> > > > > > Thanks!
> > > > > > John Johnston
> > > > > > Alberg 69
> > > > > > Sent from my iPad
> > > > > > _______________________________________________
> > > > > > These businesses support your Association:
> > > > > > http://www.alberg30.org/store/A30supporters.html
> > > > > > Please support them.
> > > > > > _______________________________________________
> > > > > > Public-List mailing list
> > > > > > Public-List at lists.alberg30.org
> > > > > > http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
> > > > > > _______________________________________________
> > > > > > These businesses support your Association:
> > > > > > http://www.alberg30.org/store/A30supporters.html
> > > > > > Please support them.
> > > > > > _______________________________________________
> > > > > > Public-List mailing list
> > > > > > Public-List at lists.alberg30.org
> > > > > > http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
> > > > > > _______________________________________________
> > > > > > These businesses support your Association:
> > > > > > http://www.alberg30.org/store/A30supporters.html
> > > > > > Please support them.
> > > > > > _______________________________________________
> > > > > > Public-List mailing list
> > > > > > Public-List at lists.alberg30.org
> > > > > > http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
> > > 
> > > _______________________________________________
> > > These businesses support your Association:
> > > http://www.alberg30.org/store/A30supporters.html
> > > Please support them.
> > > _______________________________________________
> > > Public-List mailing list
> > > Public-List at lists.alberg30.org
> > > http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
> > 
> > _______________________________________________
> > These businesses support your Association:
> > http://www.alberg30.org/store/A30supporters.html
> > Please support them.
> > _______________________________________________
> > Public-List mailing list
> > Public-List at lists.alberg30.org
> > http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
> 
> _______________________________________________
> These businesses support your Association:
> http://www.alberg30.org/store/A30supporters.html
> Please support them.
> _______________________________________________
> Public-List mailing list
> Public-List at lists.alberg30.org
> http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org

More information about the Public-List mailing list