Planing Trimarans

Discussion in 'Multihulls' started by Doug Lord, Sep 30, 2006.

  1. CT 249
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    CT 249 Senior Member

    What boat can be supported by hydrodynamic lift only? There's a thread here by skiff designer Alan Smith that says (I think) even an 18 Foot Skiff going flat-stick has something like 30% of its displacement supported by buoyancy. Ergo, no dinghy or skiff planes according to your definition. That seems a bit harsh.

    Thinking of the waterflow over my speed and slalom boards makes me think they have an element - very small, but still present; of buoyancy lift. So it seems that neither speed boards or even water skis at slow speeds plane under the proposed definition that all lift must be dynamic.

    Isn't there a fairly commonly expressed definition that planing is when dynamic lift lifts the boat's centre of gravity above its static level? While it's not really practical to work out, it is a distinct line between planing nad non planing.
     
  2. mike leneman
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    mike leneman Junior Member

    planning

    Well, I think that is what Chris and I have been saying all along. The hydrodynamic lift is always just a percentage of the overall lift. On a planning sailboard or skiff, etc. the percentage of hydrodynamic lift compared to static lift is pretty high......and look at the shape and area for planning. It's flat and a pretty big (as a percentage of boat) area as well.
    This is not the case for the center hull of a Farrier tri. There is a pretty small area, it's not flat, there is a lot of rocker and the percentage of lift is pretty small.......I'd say less than 10%, if that much.
    Cheers,
    Mike
     
  3. peerliane
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    peerliane Junior Member

    Thank you Mike
    You are probably right about the time schedule but we give is goals like this to go forward. It's intersting to know that someone as already used ply and styrene sandwich. What kind of glue did you use?

    About the design, I have to say that it is not because few people did follow this way that it is a wrong one. Designers and racers often do things wich are "already working". Look at these maxi multihulls (like 60 foot open before) ; they are all cats but tris are coming and I bet in few years there will only be tris... And it's not a matter of available material at the time. So let's carry on and we will see...
     
  4. mike leneman
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    mike leneman Junior Member

    big tri

    Peerlaine,
    We used epoxy with fillers to bond the styrene foam to the plywood, then we glass the plywood with light cloth and epoxy.
    Keep on building ! and keep us updated on the progress..........
    Unfortunately these projects always take longer than we think.
    Cheers,
    Mike Leneman
     
  5. sailsocal
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    sailsocal Junior Member

    Did you do any computer simulations or build scale models of this design before starting construction?
     
  6. peerliane
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    peerliane Junior Member

    We did some calculations before starting anything and we also built dinghyes .On the computer the shape of the mains and of the floats start to give significant lift at 5 knotsof speed. What we are trying to imagine is the behavior of such triangle shape hull when it hits a wave; and we couldn't find any computer program able to predict this. Nothing is better than a full scale experiment. Given the price and the ease of building, we thing that it won't be a big problem to re-buid the amas afterwards for a more classical shape...
    To Chris, I want to say that we are using polyurethane glue (the one that foams a littke bit) that goes inside the polystyrene foam ( 2 to 3 millimeters) , the bonding is very good. This glue is easy to use (no mix, sprayable) and cheap.
    Sorry not to answer very quickly to the post; we are working hard ( and hot right now!)in the shed wich is computer equiped but no link to the web.
     
  7. Dan S
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    Dan S Junior Member

    Can you say lame name recognition!!!
     
  8. Pericles
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    Pericles Senior Member

  9. lorenzo98
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    lorenzo98 builder

  10. grumpy old man
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    grumpy old man Junior Member

    there is no lift created by a canted windsurfer rig all the pressure is downwards through the mast base or the sailors feet otherwise the windsurfer would be impossible to control... try ít and see.... the lad in the picture is bunny hopping over a wave and has been captured in a moment of time ... his next action is to put pressure down with his feet because if he loads up the rig he'll just nose dive ... wind surfers are the ideal medium to discover what happens at the point of planing because the board and rig are an extention of your body and you feel every nuance of what the forces and resistances are ....no maths theories needed .....ur either planing or ur not thers nothing in between
     
  11. grumpy old man
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    grumpy old man Junior Member

    if a planing tri is the way of the future then get a volvo 60 dump the lead attatch some outriggers and break a few world sailing records ... it would save a fortune in R&D ... i think not ..... mr farriers use of a center hull design that uses hydrodynamic lift to reduce W.S.Area and form drag by taking advantage of the transfer of displacement to the outrigger is not original.. but the fact that he has used this concept successfully in a comercially produced trimaran is .. he has been able to get the best compromise between hull volume and speed by producing a shape that will plane when the distibution of righting moment , displacement and boat speed are in balance (any body who has sailed a sinker sailboard will know exactly what i mean) ... His boats no doubt perform very well and the sensation of acceleration as the main hull drops the drag and the lee float loads up would give the impression that the whole boat is 'planing' . but a cat doing the 'wild thing 'experiences that same surge of acceleration from similar forces and they dont plane... planing trimarans dead down wind in a gale maybe .. in real life nah
     
  12. Doug Lord

    Doug Lord Guest

    ===================================
    Besides the fact that a couple of the worlds best trimaran designers claim that their hulls plane(Farrier-main ; Antrim-ama) the same old same old just goes on and on and on.
    From a Weta ad: " Sails like a fast planing dinghy, but without the fear of capsizing." And there is even a new design that calls itself a "trimaran/skiff". Now no one in their right mind would name a boat a "trimaran/skiff" if the main hull didn't plane,would they?
    http://windcraft.net/index.php?option=com_content&task=view&id=144&Itemid=56
    -----------------
    Boating New Zealand claims the Weta main hull planes: http://www.tcdesign.co.nz/Weta_A4x2.pdf
     
  13. tobybirch007
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    tobybirch007 New Member

    I'm not sure this is the ideal thread to make my first post, but I'm going to risk it anyway. I also didn't read this entire thread, it's just too long. But, I can't resist commenting on this subject.

    My view of a planing hull would be one the rises out of moving water on it's own, with no power needed. I think a good way to test whether or not a hull is planing would be to attach an un-masted hull in a fixed location in a moving stream.

    I believe the planing effect is caused by the vertical component of force when the fluid encounters a plane (hull). It's exactly like what happens when you stick your hand out of a car speeding down the highway. In a nonmoving boat, there is no planing force, therefore the weight of the boat is countered by the weight of the water displaced, causing it to float (steady state).

    When a moving boat has a surface below the waterline, the force exerted on the hull is directed upward or downward (depending on the surface orientation) as well as in the direction of the original force. This is true unless the plane is exactly parallel or perpendicular to the fluid flow. The weight of a boat is lessened by this force, causing it to rise in the water in order to displace less water, seeking a steady state.

    So, any hull I've ever seen will plane, it's just a question of whether or not the boat is loaded correctly and going fast enough. Also, on some level, all boats do plane.

    I think the question should be "Does this boat plane significantly at realistic speeds to be considered a planing hull?"

    And just to weigh in, I believe the farrier boats do not plane. I think the rising main hull is do to heeling about the ama. But, it is possible that the main hull is planing, causing the ama to bear large side-wind forces that make it appear to be bearing the weight of the hull...
     
  14. Chris Ostlind

    Chris Ostlind Previous Member



    Other than the above conclusion as a representation of pretzel logic, some would say that the original nomenclature is pure genius.
     

  15. grumpy old man
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    grumpy old man Junior Member

    :D :D :D :D :D :D :D :D :D :D :D :D :D
     
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