Dorado 30 High speed stability

Discussion in 'Powerboats' started by Austin, Apr 24, 2020.

  1. Austin
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    Austin Junior Member

    here's the boat running 22 SMPh in 2-3 rollers

     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    That boat seems to be trimming down at the stern, is yours like that ? Those motors do seem like overkill for a hull like that, especially if the boat gets skittish short of 30 mph.
     
  3. Austin
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    Austin Junior Member

    Yes, that is my exact boat.

    The idea is to modify the boat accommodate more power and speed
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    The video sort of suggests the centre of gravity is fairly well aft, hardly surprising, there is basically just fresh air in the forward half. You would not call that an offshore boat, the ride would be not up to scratch, and broaching a real risk. If it is easily done, I would raise the engines, if you encounter ventilation, trimming the engines down might give you a little margin. It's all work, though. Easier than hull modifications, though. I think I'd like to see a shorter pod as well. Not so easy, though.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    What was it converted from ? Transom hung outboards ?
     
  6. Austin
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    Austin Junior Member

    Center mounted Diesel jack shafted to an outdrive
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    And was the skittishness evident then, or it never got to that speed ? What hp ?
     
  8. Austin
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    Austin Junior Member

    I purchased the boat after being converted to outboards.

    I believe the largest Diesel that was put in was a 300hp diesel, Some boats came from the factory with single and twin mounted outboards.

    The fuel tank is installed where the diesel engine used to be to equal out the weight.
     
  9. Austin
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    Austin Junior Member

    here is a Dorado 30 with a single 300 running 1-2 chop. roughly 22 SMPH with trim tabs down.

     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    If that pod is as long as you say, then I think the centre of lateral resistance is too far aft, with two outboard legs involved. How different that would be, to the single sterndrive. With deep vees and pods, there is plenty of boat still in the water at that speed, your outboard legs are a substantial profile in the water, while the flattish bottom is skating along, riding high. That it only develops when pushed for more speed, seems to support that idea.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    The yellow boat seems better balanced, especially considering there are a couple of bozos right aft. Shorter pod ? Single engine a lot less weight perched out there.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    Get an axe and chop one of the motors off the back. Might be all it needs. :eek:
     
  13. Yellowjacket
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    Yellowjacket Senior Member

    There was thread on here recently with a number of problems that were associated with the long pod on the aft end. If the flow under the pod is separating all is fine, but if it's wet then there are going to be issues with it pulling down the transom. The first thing you need to do is determine if the flow is reattaching to the pod aft of the transom. So long as it's not reattaching you should be fine. If it is reattaching you're going to have problems. This is a long pod and there aren't any strakes or surfaces back there to keep the hull going straight. Still, you're overhanging a lot of weight way aft of transom and that's going to create a lot of problems, starting with getting the bow too high. Also, you said this boat is converted from an outdrive. You need to look at the keel and make sure it's straight. If there is any hook or rocker to the bottom that needs to be addressed first. Hook will make the bow dig in at higher speeds, resulting in bow steering and instability.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Re the pod, it isn't possible to say much looking at the pix, but I would say by the drain plug in it being positioned at the forward end of it, it has negative attack angle.
     

  15. Austin
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    Austin Junior Member

    Here are some pictures.

    I’m positive the water separates from the pod. And the hull appears to be very flat
     

    Attached Files:

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