[Public-list] prop and elec questions

[Mike Lehman]

Dan,

I believe you have an Atomic 4, is that right? The A4 is a direct drive. At 
wide open it runs about 1400 RPM which produces about 5.5 knts, more-or-less 
depending on condition of your bottom, your prop pitch [originally 13x7], 
wind and waves. Based on that you can interpolate to get the approximate RPM 
for 3 knts. It won't be precise but the numbers are so low that the error 
margin won't mean much...you could estimate it to be 750-850 RPM. for 
example.



Mike Lehman
~~~_/)_/)~~_/)~~~




----Original Message Follows----
From: Jonathan Whittingham <whittle at shaw.ca>
Reply-To: Alberg 30 Public List -- open to all <public-list at alberg30.org>
To: Alberg 30 Public List -- open to all <public-list at alberg30.org>
Subject: Re: [Public-list] prop and elec questions
Date: Wed, 29 Jun 2005 10:33:22 -0700

dan walker wrote:

>i have asked the electric propulsion guru to let me know how long to sail 
>at three knots to recharge the batteries in the setup i am considering.
>he threw back some questions that i do not have answers to at my 
>fingertips.
>at what engine rpm will our boats with the two blade prop move at three 
>knots,and what is the largest diameter prop we can put on an alberg.
>appreciate responses. thanks
>dan
>rascal 145
>
>
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Dear Dan,
             13" diameter is the largest prop size for the Alberg 30. Speed 
performance relative to Engine RPM depends on a number of factors, not least 
of which is Prop pitch. Having said that my new Sole 26HP diesel with a 
13x9.5 prop is running 3 knots at about 1000 rpm. I was getting 6.5 knots at 
2500 the other day.Propcalc which is availible from the Alberg30 site 
confirmed what the experts told me about sizing my prop to the engine. They 
appear to have been correct!. Regards Jonathan Whittingham.

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