why are all cats like this ??????

Discussion in 'Multihulls' started by krishkannu, Apr 6, 2012.

  1. krishkannu
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    krishkannu New Member

    i am doing a project in cat design n ,happen to notice, that in all cats the cross structure does not extend out of demihulls in p/s sides.
    can any one could tell me the possile reasons for that ?:confused:

    also what can be advantages of this newer design over the old pattern
     
  2. jehardiman
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    jehardiman Senior Member

    Cats are weight limited and already very beamy for thier length, therefore no extra weight or beam topside.
     
  3. warwick
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    warwick Senior Member

    I believe that Both Sundreamer and Stratosphere had pods extending out side the hulls.
    The way the boats were built was interesting in that both boats where built by using a part mold. Gary Bagient may be able to expand on the construction approach. Both hulls being a oval T shape.
     
  4. krishkannu
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    krishkannu New Member

    thankyou warwick...,


    my design is for an inland cat with demi hull breadth 3m and seperation of 1m, length is 20m. i am not getting enough space on the cross structure if i restrict it to hull shape (plan view). hence i was thinking of protruding the cross struct at aft and fore ends.
    i would be glad if any one could sugget me how to convince my project guide by telling him about some advantages of this design... and also how to go ahead with it...
     
  5. Alik
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    Alik Senior Member

    The answer is simple.

    The big advantage for any displacement or semi-planing cat would be to increase horizontal clearance - distance between hulls. This will allow to reduce unfavourable interaction of hulls wave systems. So we move the hulls to maximum aside, making tunnel/wetdeck as wide as possible.

    This is for certain extent, of course; for planing cats the relations are different.
     
  6. warwick
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    warwick Senior Member

    From what I can remember Sundreamer had its hulls leaning out by ten degrees, and Stratosphere had its hulls vertical. I think there was an article in a New Zealand sea spray around the early eighties. I think Gary Baigent was writing for the sea spray magazine about that time. If some knows of a link or copy of it it may be helpful. Both boats were built by David Barker an artist.

    What would have been the benefit of having the hulls angled out?
     
  7. K J Thomas
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    K J Thomas Junior Member

    Hulls angled out.

    The rational for having angled out hulls is to shorten the connecting beam structure, for lightness and strength, while still keeping a wide footprint for stability at the waterline.

    The disadvantage is the inward angled hulls lesson the righting lever at large angles of heel.

    I understand that Stratosphere and Sundreamer were built using section molds for almost all the parts.

    Gary Baigent can no doubt tell you more.
     
  8. K J Thomas
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    K J Thomas Junior Member

    The pods on Sundreamer help the feeling of space inside. Opening out at eye level in what are very narrow hulls.

    Still is a striking boat.
     
  9. warwick
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    warwick Senior Member

    That was my under stand it was built with one mold for the hull top and bottoms and one for the cross beams. was the straight mod used for the pods.

    From what I remember of stratsphere was that the hulls were 60 foot long by 3 foot wide and the the same molds used for both boats
     
  10. K J Thomas
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    K J Thomas Junior Member

    I don't remember the articles on the design well enough, but looking at Sundreamer from the front the pod cross section looks the same as the beam section.
     
  11. K J Thomas
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    K J Thomas Junior Member

  12. K J Thomas
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    K J Thomas Junior Member

  13. warwick
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    warwick Senior Member

    I may have the same problem as I don't have the articles to refer to I think there may have been one article about 1974/75 on Stratosphere which had a cross section of the hull. I thought the pods may have been the same as the cross beams.

    In some ways you could say they were ahead of their time, with the spirit 38 catamarans using a bottom molding for their hulls.
     
  14. K J Thomas
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    K J Thomas Junior Member

    The articles on Sundreamer are in the link page
     

  15. yipster
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    yipster designer

    Asymetric cat hulls had many reasonings. One famous proa witch name isnt on the tip of my tonque now, rhink it was a newick project after cheers had such ap pod on one hull that not only gave room but also improved stability and richning arm when boat turned extremly on that side, the pods boyancy came into the calcs I read, on mobile now, remember name proa and find that sidepod proa later, had not seen stratosphere and sundreamer before so thanks showing these boats!

    edit: after reading Gary's next post, rite, Dick Newicks cheers had such a pod as godiva http://www.wingo.com/newick/cheers.html but boat in mind seems to wanna stay there..
    btw: Toni Grainger reasoned uotstanding asymetric hulls could have a favorable wave interaction, more thoughts at http://www.wingo.com/proa/about/index.html
     
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