Small trimarans under 20'

Discussion in 'Multihulls' started by Doug Lord, Jun 24, 2012.

  1. Doug Lord
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    Doug Lord Flight Ready

    SewSew

    -----------------------------
    You're right, Tom but he continues to use the "scissoring" action even though that "filter" has been eliminated. The picture below was taken this year before the rudder got hit in the 2016 EC.

    [​IMG]
     
  2. Cholsson
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    Cholsson Junior Member

    If I want to add some c-foils or similar to the amas, where can I get it? Who has foils laying around to sell? :)
    Maybe Nacra 15 is the right size.

    Chris
    www.chryz10.com
     
  3. Doug Lord
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    Doug Lord Flight Ready

    Outlaw

    You seem to be very good at building and it will cost you far less(and you will learn a lot) if you design and build them.
    Is the new boat designed to fly the main hull? The answer to that will help to determine how much foil lift would be beneficial...... Take plenty of time and do careful research on foil design and construction.
    And don't forget to consider planing amas like Randy's instead of or together with foils.......
    I think you were right the first time(see below): now is probably not the time to add foils-might be better to test the boat w/o them and use whatever extra time you have to research planing amas, foil design and building.

     
  4. Cholsson
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    Cholsson Junior Member

    Chryz Outlaw in Unreal Engine 4

    I have created Chryz Outlaw in 3d, to get better understanding of the dynamics. Here is how it looks like if you want to see :)
    [​IMG]


    https://youtu.be/A2NCcMIi-40
    www.chryz10.com
    br
    Chris
     
  5. Skyak
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    Skyak Senior Member

    The limiting factor for multihull speed is diagonal stability. Your narrow placement of the beams looks like trouble. Sew Sew pivots to balance crew weight aft (so not comparable) but then it also has much shorter floats. I can see how you might think that you still have more buoyancy forward of your crew weight, but the reality is that you have severely overloaded beams.

    The narrow spaced beams on Sew Sew are BECAUSE the floats are short and small, and thus unable to generate large forces twisting and breaking the beams. It is not a tri at all. It is a radical wing dingy that a champion sailor can balance with occasional help from small floats. The main hull never leaves the water and at top speed only the main touches the water.

    Your boat appears to be a trimaran with the leeward float capable of supporting the weight of the entire craft. If you do the calculation of the bending of the forward beam, windward and main floats out of the water, from force on the sail CE with the main eased out (wind on beam or aft) I am about certain that you will find the beam breaks or at least that the deflection is excessive. What you will find from doing this calculation is that the forward beam wants to be at the mast step at least, and that the stay wants to be as far aft to the aft beam for loading, but forward for sheeting. The load path is from the stay, to bend the aft beam, torque the main hull, bend the forward beam, levered to the center of buoyancy. That's a very long springy load path so you need factors of safety in both strength and deflection.

    BTW if you are thinking that big ORMA tris have narrow beam placement, look again -their beams are more like an X than an H -so the load path is more direct -straight from the aft of one side to the forward of the other.
     
  6. Cholsson
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    Cholsson Junior Member

    OK ok Skyak. You seem to know what you are talking about. I better start building a forward beam. Maybe of an old cut of mast. And the tramp will be longer as well as Doug requested. :)
    I thought my space ship looked so cool with a small tramp. But yes it needs to handle the forces of course.
    :)
    Will do some redesign during the weekend then
     
  7. 3 in One
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    3 in One Junior Member

    Nice rendering Colson, I agree with Skyak,
    The front beam is doing most of the work, it needs to be as far forward as possible. I think aesthetics probably play a role in where they are on most boats rather than where they should be to deal with the forces. The maxi tris have it a lot further forward.
    The front beam must not only deal with the righting moment 90 degrees on the centre line of the hulls but it must also deal with torsion because the ama extending in front front of the beam is much longer than what is behind the beam, (on your boat) if there is any flex in the back beam the front beam will experience it as torsion, in other words the front beam would like to rotate when the bow or the transom of the ama moves up or down.
    On our boat the beams were bolted inboard even though I knew it should be bolted as far out as possible on the main hull. When I asked for it to be changed the boat builder was confident that the carbon beams will not deflect a lot but explained that there will be a small degree of flex.
    Interestingly we did not know how much this was until we fitted a GoPro, then we could see that the beams were flexing a lot more than we expected, so much that in very strong wind we could not maintain fore stay tension. As a result we added bolting points onto the side of the hull which immediately made it a lot stiffer. We are now bolting it internally and on the outside of the hull. During the last time we sailed it the front beams port bolt pulled out of the aluminium plate that it was fixed into. The benefit of this failure was that I could see exactly how much the beam deflected from where it is bolted inside the hull to the outboard bolt point. The forces were sufficient to bend the front beam 25mm upwards on the edge of the main hull which is only 350mm from the internal bolting point.
    We have now reinforced the carbon beams but still need to test it.
    This winter we are going to move the front beam further forward maybe even to a point in front of the mast.
    This will also bring the back beam more into the load distribution equation because it will have to deal with more of the forces from the side stays than before.
    With the bigger trampoline we would be able to move our weight further forward on the beats. Which I have already found to be a big benefit on our boat.
    I will let you know how it all works out.
     
  8. Richard Woods
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    Richard Woods Woods Designs

    Attached Files:

  9. Doug Lord
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    Doug Lord Flight Ready

    Richard what is the projected all up weight?
     
  10. Richard Woods
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    Richard Woods Woods Designs

    The main hull is 150kgs, all up about 320 depending on outriggers used

    RW
     
  11. Doug Lord
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    Doug Lord Flight Ready

    Thanks...
     
  12. Manfred.pech
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    Manfred.pech Senior Member

  13. Skyak
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    Skyak Senior Member

    Cholsson, you are a 'doer' -you don't just draw wild things, you build them and go blasting out into the ocean. We can't have you bobbing about in a pile of broken boat while we carp on about new designs.

    Trimarans are great performers, particularly when you consider the ease with which they sail fast. But they are complicated because that power (righting force) is hard to handle while keeping the boat light. You (we) need to do the calculations. The strength and deflection calculations are not just tedium. They show the sensitivity of the design to changes in dimensions or material parameters. On a boat that wide you will likely want tapered beams -uniform section of an extrusion will be heavy if it is strong and stiff enough, and per 3 in one's experience, aluminum may actually be too 'soft'. You may also be surprised that the twist of your main hull between the beams is significant to rig deflection.

    It was fun to draw your 'spaceship' (Xwing fighter inspired?) but before you take your ship to the water you need to show due respect for gravity.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Thanks, Manfred-very interesting....
     

  15. Cholsson
    Joined: Aug 2015
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    Cholsson Junior Member

    Hi! Due to all new things I have learned from Skyak and Doug Lord, I have done a new design of the hulls to reduce drag, add stability, reduce weight, and more! It also looks very sweet to me! Probably the boat will be little faster than Sew Sews Sizzor, and other wrongly designed trimarns.
    :) Br Chris!
    [​IMG]
     
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