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 Catalina 25 Specific Forum
 replacement prop		  New Topic  Topic Locked
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clayC
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USA
207 Posts
Initially Posted - 12/16/2011 :  07:33:54  Show Profile
So I purchased a new XL shaftTohatsu 9.8. It came with a four blade prop that I need to replace. What is the difference between a three blade and a four blade.

Any thoughts?
Clay C
Kamalla 1980 C25 SK/TR
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dmpilc
Master Marine Consultant

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USA
4593 Posts
Response Posted - 12/16/2011 :  08:55:19  Show Profile
Extra thrust. Click on the link below and go to the bottom of the blue-shaded box:

http://www.acepropeller.com/clinic.asp

Why do you need to replace the prop?
Edited by - dmpilc on 12/16/2011 09:01:26
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Sloop Smitten
Master Marine Consultant

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USA
1181 Posts
Response Posted - 12/16/2011 :  09:05:47  Show Profile
Clay,
If you motor long distances the 3-blade is a better option and probably give you better mileage per gallon overall. If you use the motor to primarily move around short distances the added thrust from the 4-blade will give you better control. Think of the 3-blade prop as a high gear and the 4-blade prop as a low gear. If you decide to switch someone on the forum would probably be willing to switch with you dependent on their needs.
Edited by - Sloop Smitten on 12/16/2011 09:06:46
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Stinkpotter
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Djibouti
9087 Posts
Response Posted - 12/16/2011 :  10:11:04  Show Profile
Pitch is also part of the equation. If the three blade prop is the "standard" prop for pushing light-weight boats to planing speed, it will have a higher pitch (measured in the inches that are "carved through" in one rotation), and will give you less starting and stopping power than the lower-pitched, four blade prop. Either will take you to hull-speed (the fastest you can go), but the lower-pitch will do it a a somewhat higher RPM, although not necessarily that much more throttle.
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clayC
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USA
207 Posts
Response Posted - 12/16/2011 :  10:38:05  Show Profile
I took a group of University students down the green river. I was motoring a 18 foot river cat-a-raft as a support boat while they canoed. The University has since purchased the same motor but a short shaft. It came with a three blade prop that I planed to exchange. The four prop is not ruined but it took a couple of hard wackes.

Clay C
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bigelowp
Master Marine Consultant

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USA
1797 Posts
Response Posted - 12/17/2011 :  07:12:17  Show Profile
If you sail in an area that has a strong current (river or strong tidal) I would opt to keep the four blade prop as, has been mentioned all ready, you will have greater thrust (power) which may trump speed or fuel efficiency in those conditions. BTW I have a 9.8 Tohatsu and have NEVER used a full tank during one season so I doubt the difference in fuel consumption is an issue.
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Stinkpotter
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Djibouti
9087 Posts
Response Posted - 12/18/2011 :  09:31:10  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 bigelowp</i>
<br />...so I doubt the difference in fuel consumption is an issue.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">...except when you're trying to make 50 miles with the wind on your nose (or none at all).
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clayC
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USA
207 Posts
Response Posted - 12/20/2011 :  10:04:03  Show Profile
thanks for the advice I sail on a lake so maybe i will swap with the three. sounds like a four prop would be better on a river. I sail on utah lake, no curant.
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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.