alumium catamaran mast on roof design

Discussion in 'Metal Boat Building' started by phmadeira, Jul 15, 2016.

  1. phmadeira
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    phmadeira Junior Member

    Hello
    i am designing a catamaran alumium built
    love to put the mast on the roof

    How to make sur it will be ok , strong enought...

    On the fisrt picture my first try (for now just have 120mm T bar hight on botom and 80mm T bar on top)

    the second picture is from sc 48 catamaran the only desgni i have found (look very oversysed to me)

    the two other picture is my goal (lagoon 39)

    What do you think
    thank you



    catamaran size 42 feet
    Displacement 13T
    Mast compresion 170500 Newton
    Gzmax 2.17m
     

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  2. TANSL
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    TANSL Senior Member

    You can avoid putting the pillar between the bottom and roof of the superstructure, if that's what you want, but for this you must properly size the beams and girders of the roof. Moreover, you should think that, even if reinforcements are sufficient, vibrations will occur and that the best method to avoid them is to place the pillar.
    The pillar should be a tube, preferably a circular though this is not essential, to be more effective and less weight.
     
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  3. phmadeira
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    phmadeira Junior Member

    I am planing to put a round pillar

    my propblem is to properly size the beams and girders of the roof and floor

    look like the floor beam is more importand than the roof on my first simulation

    i am tring to make some simulation under solidwork
    but i am not a specialist of this software..

    any other solution...
     

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  4. TANSL
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    TANSL Senior Member

    In your case I'd forget that software and any other, I would place an additional beam below the pillar and calculate it subjected to a point load at its center. It is a very simple study of a beam in pure bending.
    The difficult thing is not that, but calculate the compressive force on the pìllar. Can you do that?
    The whole study we are taught in the figure is very nice but is useless as you have only modeled the plates, regardless of reinforcements and reinforcements are precisely the ones who will bear this load.
     
  5. phmadeira
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    phmadeira Junior Member

    the beam did not show on the result

    the model is (see picture) it is the botton part, the top part is similar

    The difficult thing is not that, but calculate the compressive force on the pìllar.
    i know my Mast compresion is 170500 Newton , do we talk the same thing :

    Mast compresion = force on the pìllar ?
     

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  6. TANSL
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    TANSL Senior Member

    Yes, we talk about the same thing.
    A load of 170500 Newton seems rather high and it will not be easy to get a structure to support it.
     
  7. phmadeira
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    phmadeira Junior Member

    yes
    a load of 170500 Newton is the max , after the catamaran capsize if the mast or something else didn t break before

    in my case i should work at 60% percent so about 100 000 Newton
    what do you think ?

    thank
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    phmadeira

    Im a bit confused. Are you considering placing a mast on the deck and that is all,
    or
    are you placing a mast on the deck and a pillar underneath the deck that is in direct line with the mast and connects the two decks, that of of the mast and deck the pillar is on?
     
  9. phmadeira
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    phmadeira Junior Member

    are you placing a mast on the deck and a pillar underneath the deck that is in direct line with the mast and connects the two decks

    yes but the upper part is the roof
    with beams and girders of course, my problem is to size the girders

    i am trying some simulation, but not sure of the result or if my interpretation of the result is good

    on this picture
    http://www.boatdesign.net/forums/at...9398-alumium-catamaran-mast-roof-design-1.jpg

    blue part is the roof, in simulation thickeness = 5mm
    in red the grinder(the mast is bettween the to main grinder) now Tbar 120mm
    bellow the pillar round tube 200mm*10mm
    then grinder again Tbar 120mm
    bottom plate thickeness = 5mm









    that of of the mast and deck the pillar is on?
    didn t understood this part....
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    Then it is very straight forward. No 'simulation' required.

    Since the two decks are connected by the pillar, all you have to account for is the transfer of shear load. Since the two decks that are connected shall act together as one (like any truss/link-span) and thus be very stiff, but, it will only do so, if you have sufficient shear area to transfer the load from the pillar to the supporting structure at the ends of the decks. If there is insufficient shear area, then the pillar shall attempt to penetrate the decks when under the mast load.

    Then after that check, you need to ensure the connection at the ends of the deck - where this shear load is transferred - has sufficient shear area itself. Otherwise this shall fail.
     
  11. phmadeira
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    phmadeira Junior Member

    thank
    look easy for you Ad Hoc, not really for me
    i know just a bit on this subject , and also always get very confused as my English is not my native language

    how to i know (calculate) the shear area to transfer, to make sure i do have sufficient area

    thank
     
  12. Ad Hoc
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    Ad Hoc Naval Architect


    Then you should not be attempting this. You should pay a naval architect/structural engineer to do this for you. Get it wrong and the lives of those on-board are on you…

    See image below:

    Mast-Beam.jpg

    You don’t need numbers…just understanding of the structural mechanics. Image 1, the 2 decks are shown on the left hand side, then apply the mast load. With no connection (or strength in the upper deck) the deck shall simply bend as shown on the right.

    2) place a pillar connecting the 2 decks, apply the load, if the decks are weak it shall penetrate the lower deck, if the decks have some stiffness then the decks shall deform as shown on the right.

    3) Now, place shear members (struts/tie bars/beams) connecting the pillar – where the load is being applied – to the 2 decks as shown. Once the load is applied as shown on the right, the arrangement acts as one structure and is very stiff. It then simply transfers the load from the pillar via the shear members to the ends.

    4) Same as no.3) except you now have deck beams doing the job, but a connection from the 2 decks is still required, shown by the curvy bracket. Result on the right is the same.

    5) Once the load is transferred to the ends, the attachments also need to absorb this shear load – are the ends stiff enough and have sufficient shear rea.

    That is it.
     
  13. phmadeira
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    phmadeira Junior Member

    Corection
    a load of 170500 Newton is the max , after the catamaran capsize if the mast or something else didn t break before

    corection : 170500 Newton is the max at this point windward hull is just flyning

    10 degree heel : 130 000 Newton
    7,5 degree heel:100 000 Newton

    in my simulation 120mm T bar Look OK with 100 000 Newton

    Also i think i do have to check the supported compresion of the mast before breaking
    and just propably add 5,10% security factor ?
     

  14. phmadeira
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    phmadeira Junior Member

    102 000 Newton
    it is also the time to reef
     
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