[Public-List] propeller

[via Public-List]

if the prop does not 'slip' it can do no work to move the boat. 

Alternate to the screw idea , there are two other concepts useful to understand and model propellers

One is the idea that it is a pump accelerating water aft ward , exchanging momentum to drive the boat forward. 

The other is that it is a distributed wing. Cut through a prop blade spinning as the boat moves forward, and you see a wing section at a small angle of attack. It's lift is forward , providing thrust, and its drag is tangential , providing the torque the engine overcomes.


Mike

Michael J. Meinhold 
meinhold272 at gmail.com / 301 852 0619

> On Feb 24, 2016, at 8:29 AM, Gordon Laco via Public-List <public-list at lists.alberg30.org> wrote:
> 
> Or another way to understand 'slip' is to consider the propeller as a screw (which it is).   If the prop is said to have a 7" pitch, that means that if it were in a solid substance like wood, it would advance 7" every full rotation.  
> 
> Well it's not in wood, its in water, so every full rotation of the prop only moves it (and the boat it's attached to) forward about 3.5".... So the 'slip' is said to be about 50%.  
> 
> Interesting stuff
> 
> Gord 426 Surprise.  
> 
>> On 2016-02-23, at 10:18 PM, Chip Dance via Public-List <public-list at lists.alberg30.org> wrote:
>> 
>> 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
>>> _______________________________________________
>>> 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