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Big Motor Big Prop Mounting Height Jackplate

Discussion in 'Members Zone: Props and Power' started by JDB, Sep 7, 2018.

  1. JDB

    JDB Member

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    For the few that might be interested in this I wanted to share my limited experience and thoughts on motor mounting height.

    I will start by saying that I'm no expert and have owned tuned or tweaked a total of two pontoon boats with the first one being a 16ft no name twin tube 40HP 2 stroke and then later adding a 90HP 4 stroke and then a water glide.
    The second is the Benny in my sig which is an amazing boat and I am so glad to have found in good used condition with the shorter fencing And the ESP.
    I really dislike the new taller fencing. Not on a fishing boat. Like fishing from inside a cage.:(

    On to my current setup:
    Started out in the Lowest motor height but now I am in the lowest hole / highest motor height position which puts the anti ventilation plate at 1.25" above the bottom of the tube.
    Holeshot is still outstanding although rarely fully used.
    No ventilation in the turns or ever.
    Top Speed increase, I estimate to be around 1/2 MPH thus far.
    Less Motor depth in our Very Rocky lake is a big plus.
    Engine no longer hits the fuel tank at full tilt which was a pain for years.

    Obviously Bennington designed the transom - 25" Esp for a multitude of applications but I'm thinking the Bigger motors and props could use an even higher mount height options than it offers.

    What to do from here:
    Live with and Enjoy the already great but possibly not the Best Performance?
    Drill New mounting holes and continue to raise and experiment? (Don't even imagine a hand drilled, butchered up, wallowed out hole job here cuz that ain't happening)
    Install a Jackplate which brings added cost, added weight and some level of Added effective motor weight?

    No need to debate warranty issues here as that has been covered in other threads.

    I understand that props play a big role in this and I'm looking for great All Around Performance and assume most of us are.

    The 50mph Benningtons are far too rare IMO.

    Thoughts Guys and Gals?

    JDB
     
    Last edited: Sep 10, 2018
  2. JDB

    JDB Member

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    F250 Offshore Bennington Height.jpg
     
  3. lakeliving

    lakeliving Well-Known Member

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    Interesting. I raised mine one hole up with my SPS setup and noticed a reduction in tight turning ability as it will cavitate under a really sharp turn unlike before. It's not an issue for us since we're not doing water sports and I picked up a little straight line speed.
     
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  4. Jb75

    Jb75 Well-Known Member

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    I'm with lakeliving. I've raised mine one Hole and definetely cavitate more in aggressive turns. Picked up an mph or two but also affected the wake for skiing in an adverse way. Mine will go back down next time I'm out of the water. But I am curious JDB about your setup. I'm running an ESP 250 sho with 3 blade Yamaha swsII prop (15 1/2x16 pitch). What prop are you running as it seems your hooked up well and at a considerably higher mount.
     
  5. JDB

    JDB Member

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    Lakeliving, Is that one hole up from lowest?
    When you say tight turn do you mean crank the wheel to the stop at full speed?
    What Prop is on that F200? Is that the new 4 cylinder?
    So many variables. One mans tight turn is another mans "threw women and children over the fencing"
    No experience with an SPS but these high powered ESP's will really really pull some G's in the turns.

    JB75 - One hole up from lowest?
    Im curious how you trim it? Middle on gauge? Trim down for sharp turns?
    Is that the 25" SHO?
    I am currently running the same prop you are.
    Can you measure your prop centerline relative to bottom of tube?
    Not sure of the difference, if any between the offshore 25" and the SHO 25" but prop centerline height removes all variables including the motor mount design changes or the hole pattern placement relative to tube bottom.

    Next time I go out I will check the Aggressive Turns more thoroughly.
    FWIW I'm at 7" below tube on the Prop Shaft Centerline and again that is the highest motor mounting height on this ESP with an Offshore 250 Yamaha.
     
  6. Jb75

    Jb75 Well-Known Member

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    Yes I'm one hole up from the lowest. Also it is the 25" shaft. My guess is lakeliving and myself crank that wheel a touch more than you in the corners. Although I even experience more ventilation from a start. None of this is unexpected mind you and most can be handled with trim. But even trimmed all the way in I've lost grip in aggressive turns. I'll measure centerline sometime for you but I stay in the water year round and have no trailer. I'll try next time I get a nice day at the sandbar. Always crazy how different boat setup can be.
     
  7. Jb75

    Jb75 Well-Known Member

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    Sorry, meant to say most of this is expected. I realized I'd likely lose some grip but I just had to find out how it ran getting that cav plate closer to the surface. With my 17 pitch I could push it over 50 I just couldn't handle the non sds hub and subsequent low rpm vibration of the Solas prop. May get some work done to the Yamaha prop this winter and bring it up a bit in pitch and maybe cup
     
  8. mbhenry1955

    mbhenry1955 Well-Known Member

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    I have a 2250 ESP with a 250 Honda. My engine is mounted 1 hole up and I'm turning a 14 X 19 Mercury Enertia.
    This prop is outstanding. Great out of hole performance with a great top end (50@6100). I get VERY little cavition with this prop
    and with it trimmed down, it's had to get to cavitate on hard turns.
     
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  9. lakeliving

    lakeliving Well-Known Member

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    Mine is one up from the bottom and when I power turn, I power turn.

    I have the 4 banger with a 15” pitch reliance stainless prop.
     
  10. JDB

    JDB Member

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    A Big Thanks to those who have offered input on this and a Really Big Thanks to jb75 who might be jumping into the cold lake to measure propshaft height on a SHO equipped boat! I will be heading back to the lake in a week or so and will do some more testing.

    Thanks to yet another Mercury Enertia fan - (mbhenry1955), I will be testing the 17" version of it as well as the 16.5" version of the Monster 16" diameter Enertia Eco. I have posted a few pics of them in comparison shots. My initial thoughts are that the enertia will be too small in terms of diameter and Ear Size and the Eco will be too large but I hope to be wrong.

    The Yamaha Saltwater Series II props work really, really well and the shift dampening hub (SDS) is an added plus that really takes the Big Yamaha to the next level in Smooth, Quiet operation so the Enertia Props have a very tough act to follow but I continue hear praise from their owners so it is time for a test!
     
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  11. Jb75

    Jb75 Well-Known Member

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    Really anxious to see how you like the merc props. Been dying to get my hands on one but in the middle of a home renovation......
     
  12. JDB

    JDB Member

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    A quick update for any Performance Toon owners on the fence about purchasing or testing the highly respected Mercury Enertia Prop.

    The Enertia ECO offers no measurable increase in fuel economy on a mid to heavy weight tri-toon over the Yamaha SWS II and it gives up some top end mph. We were down 1/2 - 3/4 MPH which was not as bad as I expected for the big diameter, big eared monster.
    I suspect low speed handling around the doc or trailer would improve with the ECO but we did not have much time for that.
    The ECO is more prone to ventilation than the Enertia or The SWS II so we were able to burn it for a few seconds on a Hard Launch.
    We are not finished testing as we were pressed for time on this trip but my preliminary thought is that the Enertia Eco must have been designed to exploit Joystick Piloting on Super Sized Boats around the Dock or Slip.

    The Enertia was 1/2 to 3/4 mph faster than the SWS and stayed hooked up well under all conditions but it gave up a small amount of cruise fuel economy.
    It might be the best choice if that last Mile an Hour in top speed is really important.

    The SWS II Hooks up and launches perfectly, stays hooked up in the turns, delivers the best fuel economy at cruise - (3.3 - 3.4MPG @ 20 MPH and 3000 RPM in our case) and the SDS is a big bonus, reducing the gear engagement clunk substantially.
    It really looks to be The Best all around prop thus far, particularly on a Fish / Play boat where we might be bass fishing and casting breezy points with the big motor in and out of gear.

    More Testing to come and I am excited to test the new Dragy acceleration measuring gizmo !

    JD
     
  13. Vikingstaff

    Vikingstaff Well-Known Member

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    JDB...Your thoroughness in testing props, and then sharing our results is outstanding. We are as locked in as we are going to get with our current Merc. Enertia prop. It delivers very well for us. That said, I still like following your updates. If I ever have to replace it, it will be good to remain informed.

    Anyway, thanks for your willingness to share detailed information with all of us. It’s such a strength of these forums - the helpfulness and positive attitudes of most everyone in here.
     
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  14. RodEarl74

    RodEarl74 Well-Known Member

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    Ive tested a few different props for my 350 Verado. It came with the Mercury Enertia prop as a standard option. I always carry a spare prop incase the lake monster jumps up and bites it.

    Went with the Mercury Revolution 4 blade prop with the same diameter and pitch. Didnt really notice any difference in whole shot, low speed maneuvering around the dock or in the turns. Fuel economy was about the same also. I may have lost 1-2MPH at WOT but we dont go wide open all that often so top end isn't a primary concern.

    I think having such a big heavy boat its really hard to notice the minimal differences prop changes produce. I went back to the Enertia and kept the Revo as a spare...
     
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  15. joecfd1

    joecfd1 Active Member

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    Did you move the motor up a hole or two? I'm hearing the third hole up seems to be the sweet spot...
     
  16. RodEarl74

    RodEarl74 Well-Known Member

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    I didn’t. Would have to take it to the dealer for that since I don’t have the equipment.
     

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