Manually hydrofoil on monohull powerboat

Discussion in 'Hydrodynamics and Aerodynamics' started by Sassriverrat, Oct 4, 2017.

  1. Sassriverrat
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    Sassriverrat Junior Member

    image.jpg Hmm. Makes sense. I or someone far smarter than me would have to sit down to work the numbers but I should think the best way to solve that would be decently simple. Just like winglets on the wings on a commercial airplane, the foil would need to think its span is great than it really is. Part of this is through design of the foil itself (which is beyond me right now) but a lot of that is also through the structural engineering of the struts. If the struts were able to deliver a fairly sizeable amount of force laterally as well as vertically, this should trick the hull into thinking it was sorted by a much great base than it really is. The premise to all of this is very careful calculation in ensuring the CG of the boat is both kept low and as centered as possible, so little things like drawing off one fuel tank on one side versus equally could be very disastrous. Part of the equation for solving such issues could be through various unique designs such as making the shallow-depth keel a fresh water tank.

    Further- your design modified:
     
  2. gonzo
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    gonzo Senior Member

    Those winglets are likely to increase the moment that leads to capsizing. You need a upward and inward moment on the foil facing the inside of the turn, and an downward and inward moment on the foil facing the outside of the turn.
     
  3. BlueBell
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    BlueBell Ahhhhh...

    I don't see the point of limiting this to a monohull.
    A three legged mono-pod or a trimaran or a modified cat would even work.
    What is your objective?

    You could hang some stabilizers out the side like fish boats.
    They'd easily retract for docking.
     
  4. Sassriverrat
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    Sassriverrat Junior Member

    Gonzo- what you're saying makes sense but I'm confused on application towards my drawing. I should think that when in a turn, the inside winglet is going to now be more towards the horizontal, increasing the righting moment. The outside is going to be near the vertical which only causes a vector going horizontal into the turn. So it wouldn't pull down but it shouldn't be lifting either. Hmmm.


    Bluebell- the reason this is on a monohull is because the hull exists- it's a 90 year old New York commuter built by consolidated....she's currently finishing a 10 year air dry cycle before she's set to be refastened and glassed for preservation and strength purposes.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Again, watching boats "takeoff" on video will help explain the dynamics quite a bit. Once you reach takeoff speed, lateral stability is pretty solid, no longer being determined by hull shell/water plane interface, particularly laterally. You've developed enough lift at this point, to transfer the stability to mostly on the foils and the ride smooths out dramatically, because of it.

    The same dynamics are utilized when aircraft with dihedral, aileron bank in turns. The aspect ratio of the more horizontal wing increases lift and the same happens on a foil borne boat. This is a self leveling feature and the reason it's employed on both aircraft and foil borne watercraft. On the other hand, with high performance aircraft and foil borne boats, you may want to reconsider this feature, to gain instability, so you can ask more from the performance envelop.
     
  6. Sassriverrat
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    Sassriverrat Junior Member

    Gotcha. That makes perfect sense. That brings me to two different questions:

    1. For the takeoff- couldn't this be solved through one of two means:
    A. The lift coefficient for the sections of foil nearest the hull are very large numbers, indicating that as immersion increases, the lifting coefficient does as well and
    B. Thinking about WW2 airplanes- would independent, manually-controlled ailerons or excessive engine horsepower (or the combination thereof) both increase the lifting moments and time/distance for takeoff? I'm thinking about flaps on, for example, a 172 and the gross engine sizes (in relation to speed) of the old CAT series of WW2 planes.

    The dihedral part makes perfect sense because, as you said, it's prevalent in the aircraft. I guess that question then becomes, how do we know where the dihedral is too much because I should think with the above foil design, as we increase speed we decrease some of the foil area and thus wouldn't experience the issue?
     
    Last edited: Oct 8, 2017
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I can't see how it can work, stability wise, unless a substantial amount of foil is above the waterline at all times, such that any change in trim is countered by foil immersion that increases lift on one side/end, and lowers it on the opposite side/end of the boat. The transition phase where all the foils are still all submerged, but the boat hull no longer is, gives no initial righting moment that I can see.
     
  8. Sassriverrat
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    Sassriverrat Junior Member

    I'm a little confused what you're looking at it. My second drawing (similar to yours) allows for two "v" foils with a center foil. The center foil is designed to provide the majority of the surface area and could have an elevator flap for increased takeoff lift. The outer "v" foils provide turning stability. If need be, there could be a pair of ailerons on the wings to help with turning (and be linked via control cables to the steering which is already wire). Further, if the wing shape is not uniform along the tips, but rather the tips provide more lift than closer to the vertex of the v, it would provide additional lift at slower speeds as well as leaning into turns. Finally and still planned all along, the twin rudders, rather than being lengthened, would have angled (outwards) extensions such that the rudders acted similar to a v-tail airplane when the boat is flying (which would put the current, short rudders out of the water).
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    Assuming the foil lift is more or less equal at any depth, barring cavitation and ventilation ( correct me of that is a bad assumption), and all the lifting foils are south of the hull proper, the nett lift when the boat hull leaves the water is through the centreline, with no righting moment till some of the foils clear the water.
     
  10. Sassriverrat
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    Sassriverrat Junior Member

    Well that's what I'm trying to decide. The CG would be in between the V foils and if the transverse foil were to be generating less lift per square foot than the V foils, I feel as though the v foils are fighting and countering each other inward- creating a small right moment but one nonetheless.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

  12. gonzo
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    gonzo Senior Member

    During a turn there is an outwards force on the hull and an inwards force on the foils. It is just like a car that leans outwards of a curve. Unless you design a foil geometry that heels the boat into the turn, it will capsize.
     
  13. Sassriverrat
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    Sassriverrat Junior Member

    Gonzo- yes my method for correct that was two-fold.

    1. The current rudders on the boat are not deep and if the boat flew right now, they would not be immersed and therefore useless. So I would keep them and weld extensions that came off of them diagonally, forming an upside "v-tail" from an airplane. As the vessel turned, the inboard rudder extension would come into a vertical plane as the outboard came towards the horizontal, thus creating an inward bank. As the vessel finished the turn, centerline the rudders causes both extensions to return to equilibrium.

    2. If the rudders were not enough(I should think they would be), then ailerons could be fitted that were cable controlled with the steering wheel.
     
  14. BlueBell
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    BlueBell Ahhhhh...

    Another option would be telescoping foils that extend out the sides, beyond the hull, once away from the dock.
    These could be fully extended ( remotely ) for lift-off and gradually retract as speed increases and less foil is needed to remain "airborne".
    Ailerons could automatically control roll via an inexpensive gyro from the R/C world.
    This would allow for higher speeds due to reduced drag from unnecessary foil area.
     

  15. Sassriverrat
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    Sassriverrat Junior Member

    I've been thinking about the telescoping foil concept. My only concern with these has been two-fold:

    1. Electronical failure resulting in either inability to use something or more importantly- at speed and how the boat is controlled.

    2. With telescoping foils- these could even implement foils similar to the AC boats with a curvature designed to match the contour of the bottom such that when they are retracted, they nearly match the hull side. However, similar to a sailboat with a daggerboard- how is wear and tear minimized? Thinking about play between the board and trunk.
     
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