Re: [PSUBS-MAILIST] bionic propeller

[Marc de Piolenc <piolenc@archivale.com>]

On 11/20/2010 1:29 PM, JimToddPsub@aol.com wrote:

> As you mentioned, a larger diameter prop is somewhat more efficient than
> a smaller one. The problem is that it bumps into things and otherwise
> gets in the way.

Which brings up another motive for using a shrouded propeller (Kort 
nozzle), namely that the effective diameter of the propeller can be 
larger than its physical diameter, thanks to the stream tube distortion 
caused by the shroud. In machinery operating in air, it can allow higher 
propeller rpm without worrying about compressibility effects at the tip. 
In submersibles it's just...convenient.

> You may have seen boats used in the orient that are propelled by a long,
> hinged oar that is wagged back and forth at the rear of the boat much
> like a fish tail. Sorry I don't know what it's called. The oarsman is
> standing and the boat rocks back and forth with each stroke. I've only
> seen them in National Geographic type films. Maybe someone has eyes-on
> experience.

I think that special oar (or scull, rather) is called a yuloh.

Marc de Piolenc

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