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Prop to reduce bow rise (porpoising) in 2003 X9

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  • Prop to reduce bow rise (porpoising) in 2003 X9

    I'm looking for a new prop to reduce bow rise and eliminate the porpoising affect in a 2003 X9 with the MCX. I've talked to a couple sources, Acme, Nettles, and I've read various forum posts here and elsewhere. There's no real consistent information and clear answer. And maybe that's the answer. But I'll ask here in a new thread all the same...

    I've tried to load up weight in the bow and remove all weight from the stern. Still does it.

    I don't have the "hook" in the transom. Would rather not spend $1K+ to have that installed.

    Acme recommends their 1581 model which is 13x11.5 with 0.060 cup.

    Nettles recommends the Acme 843 which is a 13x12 with 0.080 cup.

    Both are 3 blades.

    The current prop on there is an OJ 345 which is a 3 blade 13x11.5 with 0.090 cup.

    In addition to insight on solving my porpoising problem with a prop change, if anyone knows what specific specs on a prop can create stern lift, or bow drop, I'm all ears. I'm skeptical that such a small change from what I'm currently running will make enough difference to correct the problem. But I also know small changes can make huge results. So let me know what you think.


  • #2
    I'm surprised that you have any bow rise at all in a DD, because the vector of the prop thrust is always angled downward.

    In stern drives you can play around with it a little more: adjust trim, get props with more or less rake, different diameters, three or four or five blade props, etc.

    My opinion, FWIW, is that changing props isn't going to change any problems with bow rise in a DD boat.
    Last edited by Miss Rita; 07-11-2019, 08:22 AM.


    • #3
      Some sort of wake plate is probably your best bet. A prop really isn't going to change anything IMO.


      • #4
        In agreement with other comments so far; a prop will not solve the issue. I can say that from having had this issue myself on an older model I owned several years ago. Like you, I tried everything you mentioned...the only thing (last resort) that resolved the issue was a lip (hook) on the back of the hull. Doesn't take much to make the change but that took the porpoise out of the hull.

        Your mileage may vary.


        93 190
        (safe click)
        John 14:6
        (safe click)


        • #5
          Prop has nothing to do with this, been down that path. We didn’t have the hook on ours either. The only time I experienced it was with a full tank of fuel, no passengers, and going above 30 mph. Usually on long runs from the boat launch back to the cabin. I never experienced during towing. I did run about 100lbs stuffed in the bow. If I kept the boat I probably would have added a plate but MC engineering cautioned against it as you could end up in some dangerous situations.

          What situations are you seeing porpoising?


          • #6
            At what speed is this occurring on your x9?


            • #7
              From 30 to 35 mph is the porpoise zone. If I can manage to get through it quickly I’m smooth water it settles down as it approaches 40 mph, but it doesn’t go away. It’s never that buttery smooth ride at WOT I’m used to in my old 19’ S&S. If I let the porpoising get out of control, or hit rough water, forget it, I have to throttle down or else it gets uncomfortably bouncy and dangerous.

              I’ve yet to run the gas tank down much below half. I’ve tried to offset with water in the ski locker (front) ballast only as well as 200-300 lbs of humans in the bow. None of that solves the problem.

              I’m not mad, I boat this boat with eyes wide open regarding this issue. I’m just exploring all my options (if any) before pursuing the expensive hook install.

              Love the comments. Keep them coming!


              • #8
                Add a trim tab?

                Making boomers great again!! Boomin'


                • #9
                  Mine did it also. The one thing I hated in that boat. I tried more ballast in the nose and that helped but didn’t cure it by any means. I alway thought adding a Lenco trim tab would be the best fix. That said I just sold if after 18yrs of great time with it. Our new boat has one and what a difference it makes depending on the water you can really load up the nose and watch it smooth out in rough water.


                  • #10
                    Ryan, thinking more about this I basically go two speeds in our X9
                    21.4 to foil and ~40 to barefoot. Spend very little time at any other speed, might be why this has been less of an issue for me.
                    '02 X-9
                    Lake Blue Ridge