Quadmaran project stability

Discussion in 'Stability' started by ayozeK, Sep 26, 2016.

  1. ayozeK
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    ayozeK Junior Member

    Quadmaran and Hexamaran project stability

    Hi I have created this concept to develop.

    The main points of this project are making a light central structure to reduce materials, weight and cost, using a ketch configuration of 8 automated and foldable or removable wing sails located in the "legs" of the lateral hulls and foils in all or some hulls, also the "legs" have a wing shape so they elevate or accelerate the boat.

    I describe the reasons of this design:

    -With no central hulls in the center of the boat and elevated lateral hulls I guess this boat must behave better on pitching than a trihull, it can be a quadhull 1-2-1 or a hexahull 2-2-2.
    -A quadhull 2-2 configuration must have less drag than a trihull as it happens with surfboards, a hexahull 2-2-2 will have more stability and still less drag than a quadhull 1-2-1.
    -Two deeper central hulls instead one deeper central hull must reduce roll, so the beam of the boat can be reduced, Adastra lenght-beam is 42-16, this is 37-8
    -Two engines in the center of lateral hulls also improves the boat on pitching, also modifies inertia on rolling.
    -Several fuel deposits must be located in the upper central structure to distribute weight and disipate the effect of waves, this an Adastra idea.

    A smaller version could be made of cheaps materials (plywood, cheap foam) while a passenger bigger version could be made of aluminum.

    In a 60 knots passenger version foils must be made of carbon fiber with some sort of floats or structure to create a smother landing in case of collision, the boat must work with a drone going few miles in front of her with camera and sensors.

    Also a passenger version must use waterjets.





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    Last edited: Oct 1, 2016
  2. gonzo
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    gonzo Senior Member

    I'll address your five claims:
    1) The pitching will have a different period than a monohull, but the accelerations will be higher because the forces are concentrated further from the CG.
    2)Four short hulls will have higher resistance than one single longer of the same cross section. Study hull speed limits.
    3)Two deeper central hulls compared to a single deep hull have no bearing on the rolling. To calculate rolling you can integrate, which means dividing the hull into infinitesimal lengths. When added up they give the total. Dividing them make no difference to the total.
    4)Pitching is a longitudinal movement. Moving weights laterally won't affect it. It will slow the roll period though.
    5)I am not sure what you propose is the effect of fuel tanks installed higher up or how the dissipate the effect of the waves. Could you explain it further?
     
  3. ayozeK
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    ayozeK Junior Member

    I'll try to argue the points.

    1) I guess that with the forces you mean the engine, the engines and ketch are located at the sides of the CG in the lateral hulls that must deliver a more stable propulsion.

    2) It's a trihull vs quadhull, in surfboards the central fin creates drag but that could work in quads, now this is a hexahull, so maybe it's better keeping it quad or just make a trihull.

    3) I think this effect can only be tested with a full scale model, I just think a trimaran creates a worse pendulum, otherwise you're correct.

    4) I was wrong, I meant stability through propulsion.

    5) http://www.shuttleworthdesign.com/adastra-article-part1.html
    Effect of Inertia on Pitching
    The pitch moment of inertia is the sum of the moments of inertia of all the weights in the vessel x the square of the distance of each weight from the C of R.

    It is a common misconception that a vessel will pitch either around the centre of Gravity (C of G) or the centre of the waterplane area. A fairly simple calculation of the relationship of forward momentum and rotational momentum as a vessel accelerates shows that the centre of rotation moves aft from the centre of the waterplane area, and eventually ends up about a quarter of the waterline length forward of the stern.

    It is clear then from the diagram in Fig.7 that concentrating some weight in the vessel further forward will increase the lever arm of the pitch moment of inertia, and since that effect is proportional to the square of the distance between the C of R and each weight, the effect of pitch damping can be quite dramatic. This approach has been proven on the sea trials of Adastra at full size. It is possible sometimes to create a resonant pitching frequency in the vessel that can match the frequency of the wave fronts, and then the boat will pitch more. This can be controlled by moving weight if necessary. In the case of Adastra we have fuel tanks distributed along the bottom of the hull with a capacity of about twice the normal full fuel load. This means that weight (fuel) can be moved along the hull fore and aft to create optimum trim and/or pitching control.
     
  4. gonzo
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    gonzo Senior Member

    1) No, the forces are the torques created by the wave action on the hulls. That is what causes pitching.
    2)You need to study and understand the limitation waterline imposes on hull speed. The shorter the hull the lower the hull speed.
    3)This is math; calculus to be exact. There is no need to test a full scale model. The math has been tested for over four centuries and it works. Give thanks to Newton and Liebnitz.
    5) That link is to a design with wild claims that have not much relation to reality. For example they claim they can run a 1150HP engine at 100 liters/hr. That is about half of what it will burn. You are not explaining how fuel tanks can "disipate the effect of the waves". You are not defining which effect there is you claim or how it can be dissipated.
    The moment of inertia is a quality of a body and dependent on its geometry. There is no such thing as pitch moment of inertia.
    Are you claiming you carry twice the fuel as ballast? That is quite strange.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    No-one mentions that reserve buoyancy in this prospective vessel in compromised by the very low freeboard, I could see it submarining quite easily, the unfortunates on board turning as green as the superstructure !
     
  6. gonzo
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    gonzo Senior Member

    Considering the volume of the proposed four hulls, they will be completely submerged. The extra fuel they are supposed to carry as movable ballast will make it even worse.
     
  7. ayozeK
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    ayozeK Junior Member

    The upper structure must have low weight since doesn't need a thick layer of resin, only in the bow and stern, I think 2 meters of freeboard is enough but this height hasn't been calculated.

    A real tavern is still better than a virtual tavern, enjoy your beer though.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    You would really need to know your subject matter inside out to come up with something that was a working practical vessel, rather than a gimmick. This thing looks more suited to a theme park.
     
  9. ayozeK
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    ayozeK Junior Member

    1) So when the wave is situated in the middle, it mustn't create the same torque than over a full lenght trimaran.

    2) In slim hulls at low speed, this difference can be marginal against stability gains, if using foils it's even more insignificant.

    3) There aren't quite a lot quad of hexahulls out there and in marine engineering sometimes there's a difference between reality and theory and software. You also must give thanks to the Egyptians, Phoenicians, Greeks, Romans, Spaniards and Italian renaissance scientists for boat building and science developments.

    5) To be honest I think this Adastra paper has a kind of Kellogs's carton comparative graphics, and it has some snake oil claims however it has some valid points and there aren't a lot of papers out there about this kind of boat. You may be right about the pitch on inertia, I think it's about twice fuel capacity in diferent fuel deposits so you can move the same fuel and fill bigger compartments in the desired zones, I think in this kind of boat the fuel deposit must be located in a kind of spheric keel under the upper structure to lower the center of mass.
     
  10. ayozeK
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    ayozeK Junior Member

    I haven't calculated the upper structure and overall weight, but I suppose it can be quite low, those hulls are an aproximation and could be wider and taller, a think that mustn't matter too much in slim wave piercing hulls.
     
  11. ayozeK
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    ayozeK Junior Member

    To be honest I'm not a private or public corporation and I'm afraid this kind of boat hasn't been studied, must I put a rectangle as an upper structure so you can argue about the whole concept?
     
  12. gonzo
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    gonzo Senior Member

    No, some preliminary engineering would be adequate. For example, how can you have a light structure that carries twice the amount of fuel necessary, plus passengers, water, etc. A coat or resin is not enough to build a central hull. The bow and stern would be were medium to light laminates can be used. The attachment point for the amas, legs or whatever you call them is where the maximum stress is and the heavier laminate is necessary. These are basic engineering concepts.
    Slim hulls have less stability than beamy ones.
    Making hulls wider and taller matter a huge lot on wave piercing hulls. The geometry is extremely critical. Enough so that the inventor was awarded a patent.
     
  13. ayozeK
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    ayozeK Junior Member

    It doesn't carry twice of fuel but twice of fuel deposit capacity so it can deliver greater amounts of fuel to desired zones.

    I prefer a desalination system onboard rather than a big water tank.

    I also don't want common furniture but epoxy shaped rooms with built-in wardrobes, etc.

    I meant a slim layer of resin over by several layers of thin fiber, the structure is made by CNC cuted plywood rings with holes like those metallic ones used in airplanes, the support for the fiber and resin is a layer of 30cm of glued styrofoam or another cheap light foam, that gives thermal and sound insulation.

    That structure must be done with extra of plywood skeleton and epoxy, I have thought that it could be also reinforced inside with bended aluminum pipes.

    Nice to know it.
     
  14. TANSL
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    TANSL Senior Member

    These are vague or misleading statements that can lead the OP to take wrong decisions very harmful for his project.
     

  15. gonzo
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    gonzo Senior Member

    Which one is misleading?
     
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