Re: [Amel Yacht Owners] Fixed prop


Germain Jean-Pierre <jgermain@...>
 

Hi Pat,

I am a pilot too.. though you probably have no reason to respect my opinion. :-)  

From a fluid dynamics POV, a feathered prop is better than a turning propeller.  And a turning prop has less drag than a stopped prop.

For this reason, I would not install a shaft generator on Eleuthera because of the “relative” fragility of the SM dual 90 degree gearbox and the propeller drag if left to windmill.

Cheers,

Jean-Pierre Germain
SY Eleuthera, SM 007.


On 3 Jun 2015, at 17:21, Patrick Mcaneny sailw32@... [amelyachtowners] <amelyachtowners@...> wrote:

 

Just as I sent  my question about fixed vs. unfixed props to the group , my wife sent me the results of her google search . Yachting monthly said that this subject had been debated for decades so they conducted tests that determined that a spinning prop produced less than half the drag of a fixed prop. That at seven knots you would lose approx. one knot while fixed. That seems to jive with what I experienced.  Pat
 
 
-----Original Message-----
From: sailw32@... [amelyachtowners] <amelyachtowners@...>
To: amelyachtowners <amelyachtowners@...>
Sent: Wed, Jun 3, 2015 9:26 am
Subject: [Amel Yacht Owners] Fixed prop

 
 We have a fixed prop due to the original owner opting for the prop driven alternator  , which I have dismantled since my solar panels and wind generator supplies all the electric I need. I have been told, that it is more efficient from the standpoint of drag for a prop to be fixed opposed to be freewheeling, from a pilot who's opinion I respect. While sailing I do not like to switch in and out of gear due to the loud clunk that sounds as though it could damage the transmission, so its hard to experiment to draw conclusions. However we just sailed back from the BVIs via Bermuda and we were in gear fixed and then I put it in neutral and it seemed that we picked up a knot. I never put it back in gear as we were sailing too fast and for the next three days we averaged 173 nms. with true wind avg. 12 - 16 . Could someone that is knowledgeable about props and drag tell me which is more efficient  ? I am also concerned about wear on the transmis sion while freewheeling .
Thanks, Pat SM  Shenanigans


Jean-Pierre Germain,
Chief Pilot, Cozuro Limited,
+44 7551 211 511
jp.germain@...
jp.germain@...

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