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Hi i have a 1980 striper 17 with a 2009 yamaha 90 2-stroke.
It currently has the stock prop on it wich is a 19'' pitch.
My RPM at WOT is 5200-5400 and i have a topspeed of 41-42MPH
Would it help me go faster if i put on a 19'' 4blade?
like the Mercury Trophy? or a 19'' 3blade Mercury Laser II?
And i need a hub kit for these right?
Is my current prop fine or would you recommend something else?

Thanks

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Try calling these guys. I have heard good things about them.

http://www.propgods.com/content/index.aspx

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Willem -

There are 4 factors in attaining top speed:

Mounting height of motor
Wide Open Throttle (WOT) RPM's of the motor
Diameter and Pitch of the propeller
Weight of passengers and gear

Before discussing propellers, please tell us (or post a photo) at what position the engine is on the transom. This can be described as: "all the way down" or sitting on the transom; or, "x holes up" meaning the top bolts are in X hole, counting down from the top.

For most whaler's you want the anti-cavitation plate 1 to 1 1/2 inches above the bottom of the boat when the motor is set straight vertical. Typically this means it is in the 2nd or 3rd hole from the top. This also is described as 1 or 2 holes up.

For each hole you raise it will result in the WOT RPM's to increase by ~150-200. Going up 1 hole from your current position would get you to the max WOT RPMs stated by Yamaha for that motor as seen on this page from Yamaha website assuming the same load of passengers and gear.

Hope this helps.

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Willem,

I agree with what Phil has said.

You don't tell us what propeller you have now. There is no such thing as a "stock prop", only the propeller the dealer chose to use when the motor was rigged.

In my experience, if you are getting 41-42 MPH out of a Yamaha 90 at 5200-5400 RPM on a Striper 17, you are doing pretty well.

Would another propeller gain you some speed? Perhaps, but this depends on what propeller you have now. I also suspect that any potential gain is going to be small.

If the motor is mounted all the way down on the transom, raising it one hole (3/4") may gain you a little speed by itself.

Raising the motor and a new propeller may together produce even better results, including better acceleration, fuel economy and easier handling.

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Thnx for the advice...i'll be putting a picture of the engine and prop on soon.
the prop is a 19'' pitch...black (dealers says stainless steel)
i dont think the engine mounting height is wrong but i'll check to make sure.

thanks