prop size?? 99 yamaha 90

highrisk

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Jun 3, 2011
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I have a 99 yami 90 on a 1750 (17 1/2 ft) vector hydra sports and it currently has a 19 pitch alum. prop that came with the motor when i bought it but i do not know the diameter for sure but i think its 13 1/4. Its to much i know because at full throttle trimed up high its only at 4000-4200 and it takes waaaay to long to get on a plane and seems to lose power after on a plane for a min or so. So what size would be better? is there a rpm gain rule of thumb per pitch number? like you get 500 rpm per number? So if i dropped to a 17 pitch would that put me at 5000-5200? I am a newbie so any and all info would be great! THANKS
 

highrisk

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Jun 3, 2011
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Re: prop size?? 99 yamaha 90

Anybody?? Someone surely can point me in the right direction.
 

hidef

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Re: prop size?? 99 yamaha 90

You want to decrease your pitch to get the RPMs up. Before you do that you want to make sure the Cavitation plate is even with the bottom of the hull if it sitting lower you need to raise the outboard. Once you have the height adjusted you can get the proper prop size. Rule of thumb is every 2" of pitch will change the RPM +or- 300 RPM. So dropping to a 15 should give 600 RPM you might actually want a 13" prop.
 

highrisk

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Jun 3, 2011
Messages
10
Re: prop size?? 99 yamaha 90

Yea the motor is at correct height. A friend of mine had the same set up years ago and ran a 17 pitch prop and said it was fine. But if I go in the direction of what your saying I would need a 14 or 15 pitch to get my rpms to 5000-5200 at wot. I'm a newbie but a 14 or 15 just seems like the boat would jump out of the hole and get on a plain quick but that would be about the extent of my speed is just above a plain. Let me know if maybe I'm missunderstanding. Thanks again for you help!
 
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