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 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 ...
    Life is too short for an ugly boat!


    • #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.

      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]


      • #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.