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km0e
1st Mate

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USA
30 Posts
Initially Posted - 03/11/2004 :  20:24:23  Show Profile
I acquired a 1982 C-25 this winter, moving up from a C-22. (I have a 22 for sale now). I read back through all the C-25 specific forums which are just super for information. Thanks to all of you for having this place to come to. I have a 9.9 Evinrude Sailmaster with a 91/4 x 8 prop. If I have absorbed the info I found here, That prop is 91/4 inches in diameter with a pitch of 8. What exactly does that 8 tell me? And If I gathered the info correctly, I would like to obtain (From My Local Dealer When Possible) a 91/2 to 10 by 5 to 51/2 prop. This would allow the 9.9 to still maintain hull speed but do a better job when it's rough or going into a strong headwind? Thank You, Jim Sherrow
Jim Sherrow
"Bubbles"
1982 C-25 2876 SK/SR
Lake Pomme De Terre, Missouri
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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts
Response Posted - 03/11/2004 :  21:48:56  Show Profile
The pitch (8) means that in one revolution, the blades will theoretically pull the prop through 8" of water (if there is no resistance). If the blades are flatter, they don't pull as far per revolution. The primary gain with the lower pitch is when starting and stopping around a dock. The higher pitch tends to act more like a paddle wheel, providing less directional thrust, and even tends to turn the water to froth. It is designed to push a lighter weight boat up to planing speed, which obviously it can't do with our boats. At cruising speed, both props will work--the low pitch will run at somewhat higher RPMs, which may actually be closer to the HP sweet-spot for a 2-stroke, but makes a little more noise. Against weather, it may have a slight advantage, but not as much as for starting and braking.
Edited by - Dave Bristle on 03/11/2004 21:50:59
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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts
Response Posted - 03/11/2004 :  21:49:47  Show Profile
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by km0e</i>
<br />...I have a 9.9 Evinrude Sailmaster with a 9 1/4 x 8 prop. If I have absorbed the info I found here, that prop is 9 1/4 inches in diameter with a pitch of 8. What exactly does that 8 tell me?...<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

The "8" in the prop measurement refers to the theoretical forward movement of the propeller in one revolution.
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km0e
1st Mate

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USA
30 Posts
Response Posted - 03/12/2004 :  06:33:56  Show Profile
Thank you, Now it's off to the dealer. Happy Sailing! Jim
Edited by - km0e on 03/12/2004 06:34:27
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thacket3
Navigator

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USA
101 Posts
Response Posted - 03/12/2004 :  11:58:49  Show Profile
http://www.nissanmarine.com/tech_talk/prop_chart.html

The above link is to Nissans Marines tech page regarding prop sizes and defanitions. very informative.
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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts
Response Posted - 03/12/2004 :  15:04:06  Show Profile
Here's another good link for props...

[url="http://www.mercurymarine.com/chapter_4_-_propeller_technology"]Propeller Info[/url]
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.