Too Much Hull Lift w/Rapid Deceleration

Discussion in 'Boat Design' started by rpr, Jul 2, 2023.

  1. rpr
    Joined: Jul 2023
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    rpr Junior Member

    No idea if you guys can help with this issue but it appears to be an uncommon phenomenon and I just came across this site. I have a high speed multi-species boat, a Triton 216 Fishunter, with a 300HP V8 Verado. This boat has a long lineage (used to be the Triton 215X) of porpoising issues, but the 216FH is an updated design that moved the console forward so the bow was not as light. This minimized the porpoising tendency but I have another problem with this newer model.

    If I rapidly decelerate, which is unfortunately sometimes necessary on my busy lake, the bow rises and the entire hull lifts and it feels like it’s sailing before it settles down. This is usually if I’m running at 45mph+ (WOT is 60mph+).

    I’ve lowered the motor and I’m currently running it as low as it goes, which has helped some, but the problem persists. I can almost touch the rev limiter so I’m not over propped (4-blade).

    I can’t find any other folks on the multi-species boating forums that have described this, although admittedly rapid deceleration is not something that most folks running a multi-species boat generally need to do as they’re mostly running on large open waters.

    The only thing I can think of is that the hook in my particular hull might not be enough, but that’s not something I want to try to mess with myself and overall the boat otherwise handles pretty well.

    I am running a stern lifting prop which is what this boat needs so it would stand to reason that as soon as I come off the throttle the stern might drop which could make the bow rise, but it’s pretty extreme.

    Has anyone experienced this and have any ideas what might cause it?
     
  2. jehardiman
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    jehardiman Senior Member

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  3. rpr
    Joined: Jul 2023
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    rpr Junior Member

    That’s the first rational explanation I’ve heard. The only thing that gives me pause is it’s an instantaneous thing. I can feel the bow/hull lift and the boat gets light as soon as I decelerate. Wouldn’t a stern wave take a moment to overtake me?
     
  4. jehardiman
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    jehardiman Senior Member

    Not with a hull that squats, that's why you have had to drop the prop (and the previous porpoise issue). Can you trim the unit bow down? It is all about where the CG is sitting on the hollow in the water that you make while going that fast. The stern wave is actually moving with you.
     
  5. rpr
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    rpr Junior Member

    If I understand the question that’s a bit of a subjective issue. Yes, I can get the bow down by fully trimming the motor in but I do feel like the degree to which I can control my bow with the trim is inadequate.
     
  6. jehardiman
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    jehardiman Senior Member

    Then you definitely have a squat issue. What do you think your running angle is? Can you move weight?
     
  7. rpr
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    rpr Junior Member

    I would be completely guessing on running angle. Just feels like I should be able to get the bow down more when trimmed in. As far as weight, I already try to keep my heavier gear up front. Unfortunately, replacing my 3 AGMs with LifePO4’s, which sit just in front of the console, definitely hasn’t helped me with weight distribution. But the issue existed prior to that change as well.
     
  8. fallguy
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    fallguy Senior Member

    This is not how weight changes are done on boats and the comment you make is confusing.

    If you have a 3 agm gr27s in front of the console; they create a moment in front of the lcg which is somewhere behind the console or at say 2/3rds of the waterline. Let's say 3@63 pounds @ 6 feet forward of lcg is 189•6 or a moment of 1134 foot pounds. Then you change the batteries to something lighter say 20 pound each and you reduced the weight on the bow and that moment to say 60 at 6 or 360 foot pounds which is basically like 750 foot pounds aft forgetting immersion, etc.

    While I'm an advocate for reducing the weight, in general, as you did; you eliminated a bow weight and thus effectively increased moments aft!!! The right way to do things would have been to move the lighter batteries much further forward.

    Based on this comment; it makes me wonder what other weights are aft as well.

    For running angle, put a 4' level in the boat and add washers of the same size until level bubble.
     
  9. rpr
    Joined: Jul 2023
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    rpr Junior Member

    I think we’re saying the same thing? I said replacing my AGMs with LifePO4’s, which sit in front of the console, likely made matters worse with respect to my weight distribution not helping to keep my bow down enough. Less weight up front -> more bow rise.

    Moving the LifePO4’s further forward is an option but the logistics of doing this would be difficult at best.

    As far as other weights aft, the 15EFI kicker hanging off the transom certainly isn’t helping either.

    However, this rig is supposed to be designed for that, just like most if not all other high speed walleye multi-species rigs. The Tritons unfortunately have long standing issues with porpoising and bow control. The prior 215X model was even worse. This 216 Fishunter model had the console moved forward specifically to try to address this issue.
     
  10. fallguy
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    fallguy Senior Member

    Another way to deal with porpoising is wedges. If the engine is mounted at a higher angle; it will also reduce bow lift. If it is a known problem; I would be surprised if noone has tried a set of 2-5 degree wedges.

    Anyhow, wedges would be a cheap way to stop porpoising. But keeping the bow down will still change when you drop back in the hole.
     
  11. gonzo
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    gonzo Senior Member

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  12. rpr
    Joined: Jul 2023
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    rpr Junior Member

    Yes, good thought, wedges would likely help.

    Some folks are adamant about putting trim tabs on these rigs as well. I installed Lenco trim tabs on my last rig and that definitely helped with bow control but it’s another thing to manage, it was not cheap, and as a DIY it’s not for the faint of heart.

    A new smaller pitch stern lifting prop is supposed to show up tomorrow. That will essentially exhaust prop options. I’ll see how that goes and then figure out best next steps.

    Thanks for all the tips, very helpful, and I will humbly admit I was not nearly as sensitive to the inherent stern wake issue associated with rapid deceleration as I should have been.
     
    Last edited: Jul 7, 2023

  13. BMcF
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    BMcF Senior Member

    I've always considered trim tabs to be an essential part of nearly all my boats.....several of which are pretty dependent on the tabs for achieving their best points of operation. And relatively cheap too, given the overall cost of hull, engine and electronics..
     
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