Rev 4 Experience with Twin 225 3.4L Merc

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  • Rev 4 Experience with Twin 225 3.4L Merc

    Re-powered my 25' SafeBoat this week with brand new twin Merc 225s. Engines are mounted quite high. Engines only have 7 hours on them, not sure if economy will improve with break in. Was pretty let down with performance. I feel like I need to be achieving at minimum a 2.3mpg cruise with twin 225s on a 25' Boat.

    I had the engines fully trimmed down through the duration of the test up to initial WOT at 5500rpm. Then trimming out got me to 6000 rpm and another 5+mph.


    Question for the PropGod: If I am turning a Rev 4 17p to 6,000rpm with some trim, can I move to an Enertia 19p and stay in the same RPM range and maybe pick up 5 more MPH?

    Thank you


  • #2
    For a better test, I'd suggest trimming optimally at all speeds.


    Some guys want to run them trimmed all the way down with the theory that it makes it an "even" test, but in reality, whichever prop has more sternlift, and shoves the bow down harder, and looses the economy comparison, when they may win on economy if both were trimmed correctly.

    Heck, your getting 9% better economy, and 13% faster speed at wide open, compared to your 5500 RPM numbers because you trimmed them.

    Which prop you want for "best economy" will depend on the speed you really find yourself cruising most of the time.
    The Enertia might win at faster cruise speeds.
    My bet would be on the Enertia ECO, for overall cruise economy, its hard to beat that prop on economy.
    Top speed might be 1 or 2 MPH slower then the Rev 4, but the economy is good.

    But before you dive into props, see how much of a difference trim makes.

    Ken Reeves
    [email protected]
    941-735-5808

    Comment


    • #3
      Originally posted by ken2 View Post
      For a better test, I'd suggest trimming optimally at all speeds.


      Some guys want to run them trimmed all the way down with the theory that it makes it an "even" test, but in reality, whichever prop has more sternlift, and shoves the bow down harder, and looses the economy comparison, when they may win on economy if both were trimmed correctly.

      Heck, your getting 9% better economy, and 13% faster speed at wide open, compared to your 5500 RPM numbers because you trimmed them.

      Which prop you want for "best economy" will depend on the speed you really find yourself cruising most of the time.
      The Enertia might win at faster cruise speeds.
      My bet would be on the Enertia ECO, for overall cruise economy, its hard to beat that prop on economy.
      Top speed might be 1 or 2 MPH slower then the Rev 4, but the economy is good.

      But before you dive into props, see how much of a difference trim makes.
      Hi Ken,

      Thanks very much for your reply.

      What you're talking about re: trim makes total sense for objective performance evaluation. Where I'm based in southern California, we have a near constant swell of 3-5 feet with an 8 to 12 second period. In this ocean condition, it seems like it's only 20% of the days where I would trim the motors up. Otherwise the ride is just too unstable to take advantage of trimming. This is applicable across all my boats... I own 5, all outboard powered from 24 to 36 feet and since we encounter tightly spaced swell a lot, there often seems no reason to trim up and hurt ourselves or passengers.

      I can conduct prop tests behind a breakwall and do the trimming to get best numbers and that might be a good method to objectively compare. But in the real world we are tucked all the way down on trim and and have some tab on for most days.

      I will say that I do own a set of Eco XP 16.5p and had these props on this boat previously with the twin Honda 225. I did like them a lot better and the economy was better than the Rev 4. I recall making 51mph with those as well WOT. I have them spinning on another one of my boats currently but I think I will do a test on the SafeBoat 25 again as I preferred them in all categories to the Rev 4.

      I was curious about the Enertia 19p(or 21p) as a lot of the performance reports with the Mercury 225 3.4l are published featuring this prop making very good numbers. See attached...






      Attached Files

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      • #4
        I should also add that behind the breakwall yesterday I did trim up in the midrange 3000-4000 rpm with these Rev 4s but got blow out very fast at only 20% trim.

        I like running the engines high for having them tilt high out of the water at the dock, the idea of less drag when running, and I think they just look better. My slip numbers I think are good, so that's not showing motor is too high? But they can't trim out much at all before catching air.

        Comment


        • #5
          Ahh yes, the rules are a bit different for you guys in the Pacific. and Yes, most of the guys I talk to over there have no clue about the Wide open RPM and GPS speed cause your conditions just don't really allow for it.
          But given those circumstances, you can't really compare your economy, vs the Performance reports, with absolutely nothing in the boat, on a cool day, trimmed perfectly, in perfect conditions. You'll never get close to those numbers.

          Yes, absolutely run your ECO XP's on there, I bet they do great on economy.

          The standard Enertia's are great props too, and do great on a lot of setups, but your ECO's would probably be a better choice in your particular conditions. (heavy boat, rough/lumpy conditions, slower cruise speeds)

          Ken Reeves
          [email protected]
          941-735-5808

          Comment


          • #6
            Originally posted by ken2 View Post
            Ahh yes, the rules are a bit different for you guys in the Pacific. and Yes, most of the guys I talk to over there have no clue about the Wide open RPM and GPS speed cause your conditions just don't really allow for it.
            But given those circumstances, you can't really compare your economy, vs the Performance reports, with absolutely nothing in the boat, on a cool day, trimmed perfectly, in perfect conditions. You'll never get close to those numbers.

            Yes, absolutely run your ECO XP's on there, I bet they do great on economy.

            The standard Enertia's are great props too, and do great on a lot of setups, but your ECO's would probably be a better choice in your particular conditions. (heavy boat, rough/lumpy conditions, slower cruise speeds)
            Hey Ken, you're right about those things yeah....and some of the performance report numbers will be unattainable for me.

            Looking forward to logging some numbers with the Eco and sharing back here. I would say if the Eco can't get me to 2.4mpg somewhere between 3000 and 4000 I might try the Enertia 19p.

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