Forfoot effects on planing craft

Discussion in 'Boat Design' started by Radenpm9, Oct 9, 2018.

  1. Radenpm9
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    Radenpm9 Junior Member

  2. JSL
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    JSL Senior Member

    Interesting hull: Regular monohedron (constant deadrise) with a 'bow pod' attached. Operations in following seas could be 'fun' and yet you can go around crashing into things.
     
    Last edited: Oct 10, 2018
  3. Yellowjacket
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    Yellowjacket Senior Member

    Depends on how fast you want to go. Get that going too fast and you'll find out what "bow steering" means.... The hard way!!!
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Forefoot ? I am not sure what is on display there, does that forefoot module move relative to the rest of the hull, underway, or is it locked into different positions, selected according to sea conditions ?
     
  5. JSL
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    JSL Senior Member

    Yes indeed, quite a mystery. Somethings afoot!
     
  6. BlueBell
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    BlueBell Ahhhhh...

    I would love to drive that thing in moderate seas.
    Imagine how the bow might get pushed around in current, etc.
    I'd also prefer if that "bow-dagger" was adjustable/retractable on the fly.
    I found their drawings didn't match up.
    The last two were contradictory on bow pointiness...
    Interesting how they covered (trapped) the outboards.
    I wonder how that would be in a big following sea at low speed...
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    It's a public service working river boat made at Duisburg, a German town and harbor on the Rhine, close to the frontier with Netherlands. Nothing to do with a yacht. Not intended for high speeds, nor sea. The size of the outboards comes that the Rhine current can be pretty strong, and the needed ability to help a barge in trouble. The radar is needed when you see the traffic on the Rhine, a true cramped waterway with thousands of boats of all sizes, and the thick local fogs in winter. The biggest barges on the Rhine can be 135 m long with a load of 4000 metric tons moved by a 2000 HP diesel engine so it's better to be careful.
     
    Last edited: Oct 11, 2018
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  8. Radenpm9
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    Radenpm9 Junior Member

    I imagine at high speed the boat will break the wave rather than hiking the wave contours

    I assume the forefoot locked in one particular position. Probably they want to improve seakeeping without adding too much weight (due to material weight) at fore compared to comparable deep-V fore (?)
     
  9. Yellowjacket
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    Yellowjacket Senior Member

    You miss the point. At some speed this will become dynamically unstable and this would happen in smooth water. What would happen is that the bow "fin" would dig in and the boat would spin around probably within its own length. It has nothing to do with breaking the wave, it's all about a large surface that is ahead of the center of gravity. This surface area produces increasing amounts of lateral force as the steering angle increases. So any small perturbation from straight ahead produces an increasing amount of steering force. At lower speeds the steering can respond and can overcome this force, but above a certain speed the system is dynamically unstable and if you attempted even a small amount of steering the boat would spin.
     
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  10. Radenpm9
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    Radenpm9 Junior Member

    oohh... alright now I get your point. A great perspective. Probably it is the reason they put bow thruster to compensate large lateral force. What do you think?
     
  11. BlueBell
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    BlueBell Ahhhhh...

    Do you mean use the bow thruster at speed?
    I don't think that's going to work, nor is it what it was designed for ( see post #7 ).
    Yellowjacket?
     
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  12. JSL
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    JSL Senior Member

    you are describing 'broaching' or 'broaching to'. At slow speed the boat can 'spin out' and at high speed it can spin, roll, and eject the people on board.
    Bow thrusters don't work when underway.
     
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  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Without clarification of what the bow segment is able to do, I think it is pretty useless to speculate. If it is possible to lower this forefoot in head seas, the ride might improve considerably, but obviously if running "downhill", it could lead to some dodgy handling.
     
    Last edited: Oct 13, 2018
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  14. JSL
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    JSL Senior Member

    Other features:
    The 'forefoot' is deeper than the rest of the hull so beaching is compromised.
    Hull is assembled using weld, glue, and fasteners. HuH... make up your mind. Really, how come no tape was used?
     
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  15. Yellowjacket
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    Yellowjacket Senior Member

    No, the bow thruster has nothing to with it and it wouldn't help in this situation. By the time you turned it on the event would be over.

    JSL I generally think of broaching as happening when the bow digs in because of a following wave or the effect of riding down a wave causes the bow to dig in. That is, the bow digs in mostly because the stern is lifted up by whatever means.

    Physically it's the same thing, too much bow surface area in the water, but in this case this event would happen even in calm water and without the bow being needed to be lifted up. I have experience with small jet driven boats spinning and it can happen instantaneously, but that was because there wasn't any fin on the hull. You are right, if there is enough fin area down in the water it's more probable that the boat would roll and at the same time eject anyone or anything not tied down..
     
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