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95 Bayliner 1700LS with '86 Johnson 90, only getting 5,000 RPM...prop looks terrible.

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  • 95 Bayliner 1700LS with '86 Johnson 90, only getting 5,000 RPM...prop looks terrible.

    Hello everyone & thanks in advance for your thoughts!

    I'm new to Speed Boats but have done some digging around the iBoats forum and looks like my J90 should be getting more like 5,800 at WOT. (I'm only 5,000)

    I thought I'd address this while I investigate a potential prop replacement. I hit some shallow rocks a few weekends ago which put a few pretty nasty looking new dents in the prop. It wasn't the most beautiful prop to begin with so I would LOVE your thoughts on where to start. Shall I try to file-down/repair the edges before seeking out a new propeller or just go for new?

    Thanks so much!

  • #2
    To come up with any reasonable guess for a replacement, you're going to need known performance from a prop in good condition.

    To say my terrible looking prop is only getting 5000 rpm provides NO base to build on.

    A good plan may be to figure out what size that terrible looking prop is and replace it with one just like it (undamaged of course!).

    USUALLY, if that prop doesn't prove to be ideal, it'll be close. One size up or down will be your go to prop.

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    • #3
      Originally posted by ahicks View Post
      To come up with any reasonable guess for a replacement, you're going to need known performance from a prop in good condition.

      To say my terrible looking prop is only getting 5000 rpm provides NO base to build on.

      A good plan may be to figure out what size that terrible looking prop is and replace it with one just like it (undamaged of course!).

      USUALLY, if that prop doesn't prove to be ideal, it'll be close. One size up or down will be your go to prop.
      Thank you for your response, that does make a lot of sense. To have an accurate base-line you need something to work with. I should have taken a Before-and-After, but here's the "after" image of my prop...I filed-off the bad areas and smoothed it so it's much better.

      FYI, I did a Prop search based on this style boat and it suggested a 13.25 x (17-19). My prop is a 13.25 x 15 which goes against what I have understood as a "lesser pitch increases RPM", right? "Technically", if I had 2" more pitch I'd reduce my RPM by 400 RPM (approx 200 RPM per 1" pitch).

      So, I'm thinking I need to re-evaluate this prop after I've cleaned it up. It still has a few chunks out of it so maybe this one's too far gone? I've also learned that I should be running 89 octane, not 93, so I need to re-evaluate everyting.

      Thank you again and I'd love your thoughts on this prop's condition.

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      • #4
        Need to check engine as it should turn the crap out of that `15P....
        When in doubt,Trim it out!!!
        Business Owner & Certifed Technician
        Boats I own & use
        20ft Javlin w/250 Junkrude
        17ft Bullet w/200 Merc (SOLD!!)
        13ft Allison w/150 I-6
        17ft Hydra-Sport 175GT
        15ft Allison w/75 Stinger(project)
        14 x 48 Drifter with 1100SS Merc

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        • #5
          I agree. That prop doesn't LOOK that bad in the pics. Seems like a motor in good shape would red line that prop on a light weight "speed/ski" boat. With no clue what boat you have it on, we can't even help there!

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          • #6
            I wouldn't call a 1600# 17' boat lightweight. It's rated for a 120, so under powered a bit. Prop looks ok. Engine mount height? Is av plate even or above hull bottom? Engine need an overhaul or tuneup? Iboats list the rpm for that engine at 5000 rpm, so it doesn't seem off.

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            • #7
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              Originally posted by WesNewell View Post
              I wouldn't call a 1600# 17' boat lightweight. It's rated for a 120, so under powered a bit. Prop looks ok. Engine mount height? Is av plate even or above hull bottom? Engine need an overhaul or tuneup? Iboats list the rpm for that engine at 5000 rpm, so it doesn't seem off.
              Thanks for the responses, everyone.

              Wes, thank you for that input. I looked and you are right, the original configuration was rated for 30 more horses than I've got. Engine seems to run VERY well once started but has had some cold start issues that I think I've resolved with a new fuel primer. New plugs and wires, next, as well as proper gas...I've been using 93 but 87 is what it's spec'd at, apparently. Maybe we'll push a few more RPM once that's all figured out.

              I will look at the engine height and get back to you. That's a big unknown, to me, at this point.

              Thank you for that insight, based on everything you've stated I might be close to dialed-in for the configuration. Maybe I'll keep my eyes out for a 120

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