Cobia Bay 21 w/ F150 Suggestions

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  • Cobia Bay 21 w/ F150 Suggestions

    Looking for inputs and feedback on my current setup...

    Cobia 21 Bay with Yamaha F150 (no jackplate), T-top and I usually run with 2-4 adults and 2 children on the boat. I am looking to be able to get on plane faster and maximize fuel efficiency.

    I bought the boat used and it currently has a 3-blade 14"x17P painted stainless prop. I am getting a max of 5300 RPM at 43.3mph (tested running alone) so I feel like I may be slightly over-propped since I read I should be closer to 6k rpm. It is also a little slower to get on plane when I'm fully loaded with adults then I would like.

    This has me thinking I may consider a 4-blade prop to get better hole shot. I also feel like the bow of the boat is lifting more than I would like when I am running through chop so if 4-blades help with stern lift, that should be a plus.

    Does anyone have any feedback for switching over to a 4-blade from a 3-blade? In my online research, I keep seeing that the OFX4R17P is popular but I believe each post I have seen also includes the jackplate which I don't have. I also have found a good deal locally for a PTZ4R17 but I am not familiar with the PTZ props and how they compare to the OFX. They both look to have the same 14.25 diameter. Are there any other props I should consider?

  • #2
    With my old big Parker, Ken from www.propgods.com hooked me up with a PowerTech OF (or OS OffShore?) 4-blade prop for my Suzuki DF250 and the results were de bomb! More than just the hole shot, it carried a load significantly better and I'd only drop ~200 RPMs when I had a full load on the boat. Plus the prop stayed hooked up better too.

    And yes, you are seriously over-popped, as I pitch them to be no more than 200RPMs off the max when running alone with all gear typically carried and 1/3rd fuel. Remember - Boats only get heavier as the season progresses and the bottom fouls and the OB motor performance suffers as the air gets thinner in the high heat ...

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    • #3
      The weird part of the numbers.
      F150 has a 2.0 gear ratio.
      17 pitch, 5300 RPM, at 43 MPH gives negative 1% slip. which is abnormal.

      Are you positive its 17 pitch ? cause its acting like a 19 pitch.
      Here is the performance report on that boat, obviously light load, no ttop, etc,, but you can see they have a 19 pitch, and at 5300 RPM, they are probably doing about 43 MPH. https://cobiaboats.com/wp-content/up...ay-F150TXR.pdf

      If your prop says 17 on it, maybe it has been repitched at some point in the past.

      but with no jackplate, The PTZ4 17 pitch would not be a bad one if you can get a good deal on it.
      The SCE4 would also be a good one. Both are on backorder for 3 weeks because of Covid, but that PTZ4 17 might be a good option for you.

      Ken Reeves
      [email protected]
      941-735-5808

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      • #4
        Ah, my mistake. Current prop is a 13.75x19P painted stainless.

        I wish it had negative slip though! 😉

        Thanks for the feedback. It's great to have a resource to help so I really appreciate it.

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