[PUP] :PPM-propeller efficiency

[John Marshall]

Interesting change... but does that give us maximum efficiency (fuel  
per mile) at S/L 1.2 or lower?

I have seen data that shows the latest diesel gensets have nearly the  
same fuel efficiency at 50% power as they do at 100% (although  
efficiency falls off fast below 50%).

Not sure if that relates to propulsion efficiency... gensets have to  
run at constant RPM.

John
On Nov 23, 2008, at 9:26 AM, Patrick Gerety wrote:

> ----- Original Message ----
> From: John Marshall <johnamar1101 at gmail.com>
> To:
> Passagemaking Under Power List <passagemaking-under-power at lists.samurai.com 
> >
> Sent: Sunday, November 23, 2008 10:09:25 AM
> Subject: Re: [PUP] :PPM-propeller
> efficiency
>
>> Do trawler manufacturers select the prop for perfect match at
> full RPM?
>
> In the early days at Willard Marine ('60's, '70's, '80's)  We
> always over-propped the boats.  The theory was that if you could  
> reach hull
> speed at a lower RPM, you would save wear and tear on the engine.  But
> conventional wisdom changed over the years as marine engines were  
> made more
> efficient.  Today, most marine engine manufacturers recommend a  
> running gear
> (engine, reduction gear, and prop) that will allow maximum rated RPM  
> at WOT.
> Prior to cessation of production, Willard was propping their boats  
> to achieve
> max. RPM at WOT.
>
> Patrick
> Willard 40PH
> ALOHA
> La Paz, MX
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