Multihull Collision Survivability

Discussion in 'Multihulls' started by Skint For Life, May 12, 2011.

  1. Ad Hoc
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    Ad Hoc Naval Architect

    Make up your own mind :D

    http://news.bbc.co.uk/sport2/hi/sailing/13773671.stm

    So much for those advocating a long slender hull is a "wave piercing hull" :p:p
     
  2. HakimKlunker
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    HakimKlunker Andreas der Juengere

    What do you want? The relevant wave was pierced very deeply :D
    The - emmm - boat in the clip was not severely damaged; and the crew survived (the guys on top must have had seat belts?)
     
  3. mikereed100
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    mikereed100 Junior Member

    I reckon they figure the speed is worth the occasional spectacular crash. :D
    That pitchpole probably did more for the popularity of the AC than millions of dollars of promotion! It was a nice touch sending the helmsman through the mainsail.

    Mike
     
  4. MikeJohns
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    MikeJohns Senior Member

    This power cat hit a whale a day or so back, didn't ride over it and suffered quite a bit of energy absorbtion in brittle failure. The watertight subdivision ( floatation chambers) saved the day. Interestingly they could only travel backwards otherwise the boat sank from the water forced in through the breach.
     

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  5. cavalier mk2
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    cavalier mk2 Senior Member

    Less knuckle to save a buckle? I wonder how much of the damage is construction related, an actual stem/keel forward might be an idea. Who rescued the whale?
     
  6. SouthernComfort
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    SouthernComfort Hillbilly Engineer

    What about solid hulls, with inflatable hulls inside, protected by a lightweight cylinder running the entire length of the inflatables. Have the inflatables sectioned for quicker inflation via co2. The inflatable hulls would only be filled to half of max pressure, to allow for proper distortion without damage during impact and better abrasion resistance. Maybe some kind of delayed autoswitch that engages after the outer hulls are breached, to begin inflating the inner hulls to max pressure after the danger of blowing one out has passed. Seems what I would worry about most, soft or hard hull, is the sudden stop. Doesnt matter if your boat sinks or not if you get knocked out and go overboard. Maybe some sort of crush cage in the nose to absorb impact?
     
  7. HakimKlunker
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    HakimKlunker Andreas der Juengere

    This is - in a way - the product that you just invented:
    http://www.turtlepac.com/products/underwater-lift-bags-a-yacht-floatation.html

    Easy: You put the same device around yourself.
    And so you have also invented the inflatable life jacket.
     
  8. SouthernComfort
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    SouthernComfort Hillbilly Engineer

    I should probably look a little deeper before inventing future products :p
     
  9. HakimKlunker
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    HakimKlunker Andreas der Juengere

    The world is too big to know of everything. At least, your own thought is good enough to be (successfully) commercialized. Encouraging, isn't it?
     
  10. SouthernComfort
    Joined: Jun 2011
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    SouthernComfort Hillbilly Engineer

    It is encouraging. I'm planning on building a small 16' Cat for getting to remote campsites up small rivers and creeks. Tennessee is more rock than dirt, and I hadn't even considered building anything like this into my boat. I will definately consider everything I have read on this topic. Although my top speed will be quite low, the possibility of a larger faster boat on open water hitting me is always there. Lots of good advice on this thread.
     
  11. Skint For Life
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    Skint For Life Junior Member

    Thanks for the link Hakim Klunker. I knew they existed but I'd never looked into them. So thanks, I really liked checking out the site :)
     
  12. HakimKlunker
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    HakimKlunker Andreas der Juengere

    now finally I was good for something :D
    It was a pleasure.
     
  13. Wavewacker
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    Wavewacker Senior Member

    That was entertaining...

    I'm not as salty as you guys, but I have been out there a bit and have two inflatables. Don't know what the material was on that cat....but,

    There are military RIBs that have armored material, bullet proof for small arms fire. That would obviousily be too expensive but you could use it at the bow or strategic areas.

    Another thing is that inflatable tubes can be made with waterproof pockets or containers built in, a hatch on top.

    In the drawing at the beginning of this thread, I realize it was only conceptual but tubes need a lot of framing to hold their shape.

    Inflatable materials are available that you probably would not punture them with a shipping container, never hit one, but have been around them....it would also depend on how big the boat was and the points already addressed by those with more engineering savy than I. I have hit tree branches 3 and 4 inches in diameter that I was just sure puntured mine, but no, if it is not inflated to rock hard, it keeps its form and has plenty of flex to glance off.
    After all, inflatables are used for the rapids on the Colorado and Snake where many other materials would be trashed.

    A good place to investigate inflatables and even some large tubes is "Jack's Plastic Welding"....sorry I can't provide a link.

    Happy days!
     
  14. Autodafe
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    Autodafe Senior Member

    The Dashews built Beowulf VI this way. I think there are some pictures in their blog somewhere. A much heavier cruising cat would need a lot more foam...
     

  15. truecougarblue
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    truecougarblue Junior Member

    A 10cm deep layer of foam within a bridge deck 15m X 15m on a 20 m cat would give 22.5 metric tons of displacement at very little relative additional cost to build. That would raise your inverted waterline a bit. Make it spray foam or epoxy it in and it would even enhance the structure. It also makes one think differently about any foam insulation applied to undersole both in the hulls and the deck house roof.

    This thread has given good food for thought, both on the topic, and its corollaries.
     
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