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Old 14 June 2012, 13:26   #1
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new to boating have a propeller question

I have a 11 foot Avon 310 rib. I'm using an old 1975 Johnson 9.9 seahorse motor. I need a new propeller. Any ideas on how to figure out what type size I need? I want an aluminum 3 blade but that's all I know. I have no idea about my top speed or rpms now. Any input would be of much help.

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Old 15 June 2012, 12:56   #2
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Usually (not always) the diameter and picth is stamped somewhere on the prop. Either on the outside of the body between the blades, or inside it, on the support braces.

Hard to choose a prop without knowing how the motor spins. RPM is key; speed is sort of irrelevant (unless you've got the rpm right and are looking for a tad more fast.) If the current prop is usable, take a car tach/dwell tuneup meter, and go for a ride to get rpm with the throttle wide open. That'll give you enough to rough guess what kind of pitch you'll need (assuming you find out what you've got now.)

jky
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Old 15 June 2012, 13:03   #3
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Ok thx! It says 9 1/2 X 10. I found out from Johnson evinrude it came stock w a 9 1/4 x 8. Might explain why it feels so sluggish ( besides the current condition ) thx for the idea on the tach. Are they hard to replace? It doesn't look to be much of a chore?
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Old 15 June 2012, 16:31   #4
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Quote:
Originally Posted by bicyclejuju1 View Post
I need a new propeller. Any ideas on how to figure out what type size I need?

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I maybe missing something here but your prop looks OK why do you want to replace it?
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Old 15 June 2012, 16:55   #5
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Cos the one he has is to big by the sound of it.
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Old 15 June 2012, 16:59   #6
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Cos the one he has is to big by the sound of it.
Ahh thanks - Thought it was because it had lost a bit of paint.
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Old 15 June 2012, 19:00   #7
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My neighbor who has a superior knowledge to mine about boats said it was really beaten up and I should get a new one. Then when I started looking around for a new one I discovered this one was the wrong size as well. I just bought this boat and its the first boat I've ever owned. Short of mowing the grass I have no experience with 2 stroke engines. I just moved to Florida from mtn country in the southwest so I'm familiar with skis,mtn bikes, climbing, kayaks and rafting (a different outdoor sport environment ) This boat thing is a whole new world.
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Old 15 June 2012, 19:42   #8
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Having fiddled with prop replacement choices on 8, 9.8, 15 & 20hp motors I'd say 9.25 dia and 9" pitch would be suited to a 9.9 pushing a light boat that is able to exceed planing speed.

Your old prop does look worn with uneven blade tip shaps so a replacement may give better and smoother performance.

Note on a recent replacement I had trouble with the very popular Solas Amita not performing at all well. They have changed their blade shape to more of a high thrust displacement design and I ended up getting a refund on the Solas and buying an OE prop for my Mariner 15.
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Old 15 June 2012, 20:45   #9
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Thanks for the info on solas. I was going to order one ( being their half the price of an OEM ) but I think I'll spring for the real deal. I agree with the 9. It has a 10 and was specked w an 8 so I think you're right on with the 9 recommendation. Thank you.
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