[Public-List] propeller

[Don Campbell via Public-List]

Chip:
    Slippage occurs when the prop turns and the forward motion of the boat 
is less than matching what the design of the prop ought to get, much like 
slippage on tires when the load pulled is greater than the traction 
available so the tire turns 1 revolution but the forward motion is less than 
the circumference of the tire. With 50% slip that means that the prop turns 
1 revolution and the boat goes 1/2 the designed distance of the pitch of 
that prop. While some inefficiencies are unquestionable because the surface 
of the water is not contained, so any extra force can be disbursed by 
lifting water above the normal waterline, it is sad to think that 50% of the 
designed screw is a good number for powering a boat. Too much spin on a prop 
too close to the surface will allow for cavitation, or sucking air down into 
the vortex of the prop and since gases can be compressed, even more 
inefficiencies.
Don

-----Original Message----- 
From: Chip Dance via Public-List
Sent: Tuesday, February 23, 2016 10:18 PM
To: Michael Connolly ; Alberg 30 Public List -- open to all
Subject: Re: [Public-List] propeller

Don
My limited motoring experience has only been with outboards, and, as I said
limited. Could you explain what you mean by "slip"?

Thanks
Chip

On Tue, Feb 23, 2016 at 7:55 PM, Michael Connolly via Public-List <
public-list at lists.alberg30.org> wrote:

> Charles,
> I have original set-up with Gray Marine and 13 x 9 two blade prop.
> Michael #133
>
> ----- Original Message -----
>
> From: "charles pleisse via Public-List" <public-list at lists.alberg30.org>
> To: public-list at lists.alberg30.org
> Sent: Tuesday, February 23, 2016 8:49:16 AM
> Subject: [Public-List] propeller
>
> I have the engine (original A4) out this winter so I can replace shaft and
> associated hardware and I'm thinking of trying a two blade prop for better
> sailing performance.  The current prop is a three blade 12x5.  What was
> spec'ed originally on these boats and should any consideration be given to
> the age of the engine when determining propeller pitch?
>
> Charles Pleisse
> Sookie #221
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