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Old 20 March 2016, 11:29   #1
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What prop?

Have got a yam f80 4 stroke on a 5.3m tornado. It's a new to me second hand engine that came off a larger fishing boat. It had its first outing today. The engine revs to just over 6000 rpm flat out with no trim. The current prop is 15.5 X 15-k.

I have been told that this engine should rev 5600 to 5800 rpm. And one unit increase on the pitch would bring the rpm down about 300.

Is this right?

Would a 15.5 X 16-k be the right one?
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Old 20 March 2016, 11:38   #2
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Will that be the high thrust engine since it's off a fishing boat
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Old 20 March 2016, 11:40   #3
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That I wouldn't know. How would I tell? It's a 2003 engine I think.
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Old 20 March 2016, 11:55   #4
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I might be wrong but I had a quicksilver 500 with the high thrust yam engine the pitch & diameter were pretty close same as yours.
As a comparison my rib had a 90 Suzuki with a 14 x 19 prop running at 6000 rpm an inch in pitch is equivalent to 200 rpm I put a s/s prop on 13.5 x 21 more or less same rpm.
The high thrust has the bigger gear ratio ideal for the Heaver boat worth checking out with a dealer you might be able to go up a few inch on pitch depending on what your using it for.

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Old 20 March 2016, 12:24   #5
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Just had a look the high thrust only goes up to 60 hp (T60) so it looks as though you could go to a 15.5 x 17 bringing it down to 5600 rpm.
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Old 20 March 2016, 13:18   #6
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Thanks for that. When I open it up from a standing start with the existing prop it is a bit too vicious really. If not dangerous. I think the 17 is going to be the one. An evening on the Internet it is!
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Old 20 March 2016, 13:50   #7
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When I bought my yam 60 the prop it came with was the same straight to the rev limiter from memory I went up two inch on pitch taking it to 5900 rpm but I did have a few props to try from the dealer on the Isle of Man.
Having had a look on the yam site and one other I think your 15.5 dia has certantly been propped to give thrust it looks like a 13.5 should be on it I would talk to a yam dealer before spending more cash

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Old 23 March 2016, 16:04   #8
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Gone for a 13.25 x 17k. It would appear the 15.5 diameter was wrong.
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Old 24 March 2016, 03:31   #9
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yep the motor was propped for the heaver boat anyway sorted now hope it gives you what you want Matt.

cheers
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