Re: [AtkinBoats] Gear reduction for Little Effort
- Thank you John for this and the previous posting. I'm still moving ahead on
a steam powered version of Rescue Minor and find that Bill's propeller
selection (based on prop tables and formulas - including Dave Gerr's) is
exactly right. My difference is the steam power part of the equation. Rob
White's use of a different propeller (not very different really) was based
on engine rpm (about 800 rpm faster) and the resultant hp at that rpm. But
working forward to that from Bill's propeller, it comes in about right. I've
had experience with "angled off center" props and I must say that, done
correctly, they do make for improved handling. A radical example of what
happens with an inline shaft and high horsepower and be observed when such a
boat "guns the engine" when underway.
Merry Christmas all.
----- Original Message -----
From: "John Kohnen" <jkohnen@...>
Sent: Friday, December 22, 2006 12:47 AM
Subject: Re: [AtkinBoats] Gear reduction for Little Effort
> For displacement hulls like those huge engines usually push a big, slow
> propeller is most efficient. But Little Effort is intended for planing
> speeds, so a smaller, faster propeller will work best. The propeller
> called for in the plans is 11" dia. by 12" pitch. If you can find, or
> make, a reduction gear that'll turn the shaft around 2,000 rpm that should
> be fine, but if you run a direct drive from the engine and prop it so the
> engine turns 2,000 rpm you won't get anywhere near the advertised 33 hp.
> If you can find a direct drive reverse gear you could use a cogged belt to
> the prop shaft. That'd make it easy to get just the amount of reduction
> you want.
> On Tue, 19 Dec 2006 19:27:20 -0800, Andrew wrote:
>> I'm a complete neophyte when it comes to
>> inboards. The designed engine ran at 2000 rpm with no reduction, but
>> I'm told by my marine diesel mechanic friend in Seattle that 2000
>> shaft rpm is not the norm these days, but he's used to engines larger
>> than my car
>> I'm sure prop technology has advanced some in 50
>> years. The kubota has an incredibly flat torque curve so it could be
>> happy at 1800 or 2800 rpm or whatever.
> John <jkohnen@...>
> Distrust any enterprise that requires new clothes. <Henry David
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> If you set out to build an Atkin boat, please do not modify the plans. If
> you stray from the plans you do so at your own risk and Atkin & Co. will
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