Thread: Prop Question

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  1. #1
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    Prop Question

    I have a new G3 Sportsman 17 with a Four Stroke 90 Yamaha on it. It came with a 13 1/2 x 16 aluminum prop. It currently turns 6000 rpm with ease. I want to switch to a stainless prop but im not sure what size to run. 13 1/2 x 17 or 13x18 3 blade?

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  3. Member
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    #2
    Running into that myself. I have the exact boat. I just ordered a new 18 pitch prop aluminum. I stayed with Aluminum because I recently hit a rock with my old prop going about 5 miles an hour scanning a flat. It tore up all the gears in the case/foot and I had to buy a new case etc. cost is about $1700. I was talking with the techs about the case. They said that aluminum props are designed to break if you hit something. The reason mine did not break and just bent up / ripped some blades but didn't fully break, is because I was going only 5mph. He said if I would have been going faster it would have just broke a blade on the prop and saved the $1700 repair. The aluminum props run about $125 on average.

    He recommended I stay with aluminum and would with anything under 115hps. He advised that the gears in the foot are bigger and tougher in the 115 and could handle a little more of a beating. Over all a good boat. The 18 pitch aluminum prop should give me a few more MPH.. currently I run about 40mph (GPS) at 5900 rpms (Wide open) the over rev. on that motor (F90) is 6200rpms I think. It will also drop the rpms to an estimated 5500rpms and should extend the life of the motor. I don't think it will hurt the hole shot as you know its almost instant with a 16 pitch prop.
    2015 G3 Sportsman 17
    F90 Yamaha w/ 16P prop (Stock)
    Top Speed = 40mph @ 5900rpms
    Minn Kota Maxxum 70lb, 24v trolling Motor

  4. Member
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    #3
    Let me know the results on that prop change. I have the same boat except mine is a 2016 and I have the same results as you currently.

  5. Member
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    #4
    I spoke with the techs again yesterday. They said they do not make a 18 pitch prop for the f90 and would look into either a 17 or 19 pitch props. They said they would find some and we would go over them. I'll keep you guys posted.
    Last edited by BassbossG3; 12-15-2016 at 02:52 PM.
    2015 G3 Sportsman 17
    F90 Yamaha w/ 16P prop (Stock)
    Top Speed = 40mph @ 5900rpms
    Minn Kota Maxxum 70lb, 24v trolling Motor

  6. Member
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    Dec 2016
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    Zachary Louisiana
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    #5
    This is the prop I am looking at buying. http://www.ptpropeller.com/content-p...er_yamaha.html

  7. Member
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    Alabama
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    #6
    Nice.... I'm gonna try this one http://www.overtons.com/modperl/prod...id#reviewsInfo

    The Marina said to try it if I didn't like it they would exchange it. If this one does not work I will try a 19 pitch. I don't know if I wanna step up to the 21 pitch but who knows. The stock prop gave me 5900 rpms and 40 mph. It was a Yamaha 13.5 X 16 pitch.

    It would be nice if I could find a 13.5 X 18 pitch. I think that would be the sweet spot. The F90 specs say keep it between 5000 and 6000 rpms. I think a 13.5 by 18 would put it at 5500 rpms and about 41mps.

    The 19 would put it at about 5300 rpms and maybe 42 MPH.

    I estimate that a 13X21 prop would put you at 4900 rpms which is under the spec list of 5000 and 6000 and may lug your motor causing it to be under more strain than its supposed to be, but if it does not you would be somewhere around 42.926 so roughly 43 mph.

    I get this estimation based on my on rpm / speed on the 16 pitch prop that was stock on my boat (G3 Sportsman 17 with a F90) and a simple formula I found for calculation of prop speed online. The formula is : Pitch X RPM divided by Gear Ratio X 1056 = http://www.go-fast.com/Prop_Slip_Calculator.htm

    Also I've been told for degree pitch you increase your RPMs should drop by 200. If that holds true the calculations should be spot on. Another guy told me that the RPMs would decrees an estimated 150 to 200 rpms for degree or prop pitch. It it drops by 150 per degree the calculations I posted will be off and frankly better for you with a 21 pitch prop. If someone makes modifications to any prop though it could through those calculations off. It its 150 pre degree should put you at 5150 RPMs (with in specs for the F90) with an estimated speed of 45.116 mph.

    A 19 pitch would put you at 5450rpms and 43mph with the 150 per degree calculations.
    Last edited by BassbossG3; 12-16-2016 at 09:33 AM.
    2015 G3 Sportsman 17
    F90 Yamaha w/ 16P prop (Stock)
    Top Speed = 40mph @ 5900rpms
    Minn Kota Maxxum 70lb, 24v trolling Motor

  8. Member
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    Dec 2016
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    Zachary Louisiana
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    #7
    A lot depends on how much of a load you have in your boat too. A lighter load will allow you to run a higher pitch prop. I think I am going to run the 13x18 stainless on mine. I currently have the stock 13.5x16 aluminum and from what im told going down .5 in and up 2 in pitch should put me around 5800 rpm. I can't run an aluminum prop in south Louisiana because they just don't hold up. Most of our fishing is shallow water with tons of stumps and logs in the water plus I do some fishing near the coast and the oyster beds are hell on aluminum. I think a 21 pitch will be way too much prop.

  9. Member
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    Alabama
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    #8
    I agree with you Datkins. I have not been able to find an 18 pitch prop at all. I can find 17s, 19s, 21s etc. but I have not found an 18 at all. However, I did not look for a Stainless one.
    2015 G3 Sportsman 17
    F90 Yamaha w/ 16P prop (Stock)
    Top Speed = 40mph @ 5900rpms
    Minn Kota Maxxum 70lb, 24v trolling Motor