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Old 26 August 2012, 13:05   #1
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Yamaha 75 on SR5

After several months hunting for an appropriate engine to replace the Merc 80 we have bought a Yamaha 75 2 stroke.

The engine isnt in the first flush of youth but runs beautifully after sorting a few teething problems.

I had it out for the first time today and I was pleased with the way it run, it never missed a beat, I do have an issue though and hoping someone can point me in the right direction.

As Ive said its a Yam 75 on a Searider 5.4, the prop is a 13 1/4 x 17 K series, its all been setup as per the recommendations on here with the anti vent plate level with the deepest part of the hull, the problem is that no matter how I trim it I cant get more than 4800 revs out of it, this equates to 31knts. I was hoping to get up near the 5200-5500 range.

I admit the prop isnt brand new and has a couple of minor dings in it but nothing major.

Would 19" be the way to go? My understanding is that that would bring the revs DOWN though? A new 17? Or am I looking in the wrong direction?

These RIBs dont half like a drink though eh!?
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Old 26 August 2012, 13:47   #2
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How dinged is it and is there any slime on the boat?
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Old 26 August 2012, 13:59   #3
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How dinged is it and is there any slime on the boat?
The boat has been out of the water for 12 years and is very clean, a few scratches but all in all its in good nick.

As for the prop, its just dings, no chunks missing. One of the blades might have a bend in it but almost unoticeable without using a straight edge to check.
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Old 26 August 2012, 15:28   #4
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Your prop needs to be in good condition to start with .
Have a look through the posts on here there will most likley be someone with the same setup and see what size prop they are using .
You need to know its not an engine issue and that your engine will reach full rpm if so to increase the revs you will need to come down on the pitch ,i think every inch is about 400 - 500 rpm
When you are sure its the prop you need to change speak to a specialist for advice i can recommend Steel Developments and try and borrow another prop to try Home page
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Old 26 August 2012, 15:56   #5
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Originally Posted by Jonny H View Post
Your prop needs to be in good condition to start with .
Have a look through the posts on here there will most likley be someone with the same setup and see what size prop they are using .
You need to know its not an engine issue and that your engine will reach full rpm if so to increase the revs you will need to come down on the pitch ,i think every inch is about 400 - 500 rpm
When you are sure its the prop you need to change speak to a specialist for advice i can recommend Steel Developments and try and borrow another prop to try Home page
I had a look through related posts earlier today and it seems to be the 17" and 19" are the props of choice.

Im liking the look of the Steel Developments prop service, for 40 I could have a good as new prop, its a no brainer really.

Il hunt for another K series 17" to see if the performance is the same as my one.
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Old 26 August 2012, 16:17   #6
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Give them a call for their advice they have been in the business for years and really know their stuff and also have used props in stock as well
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