How big would a catamaran have to be...?

Discussion in 'Multihulls' started by dustman, Apr 23, 2021.

  1. dustman
    Joined: Jun 2019
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    dustman Junior Member

    How big would a catamaran have to be... to basically be immune to capsize in any circumstance that may be encountered? Let's say you drop your sails, raise your daggerboards and are stuck in the worst part of a bad hurricane, just drifting, no drogue, no propulsion, no steerage, no nothing.

    Assumptions: Very low freeboard, rounded hull bottoms, low center of gravity, low windage, high strength structure.

    Just a thought experiment, so be nice.
     
  2. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Dustman. 600 foot ships have had there bows broken off in a seaway. Well designed cruising sailing cats up to 55 foot have been capsized by wave action (Google capsize of Anna catamaran). Yes, you can have a near bullet proof 60 foot cat that has low windage and reasonably heavy displacement but you can still be caught out by pitchpoling. A study done in Britain (Google Multihull Design Considerations for Seaworthiness) basically concluded that a cat can be in danger of wave capsize when the wave height is greater than the beam of the cat. PS In the US insurance rates for cats can be lower than mono's as cats are considered safer.
     

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  3. jehardiman
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    jehardiman Senior Member

    Approx 7,000 nautical miles length by 7,000 nautical miles beam.....Oh, and you have to be aground... pretty much what oldMulti said.
     
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  4. Mr Efficiency
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    Mr Efficiency Senior Member

    They say the Queen Mary passenger liner carrying quite a few thousand troops went over to 52 degrees or thereabouts in a North Atlantic gale, a couple of degrees more and it wouldn't have come back, so all bets are off about the 55 foot catamaran.
     
  5. fallguy
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    fallguy Senior Member

    I'll be the guy.

    submarine
     
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  6. dustman
    Joined: Jun 2019
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    dustman Junior Member

    Thanks Oldmulti for a reasonable response. I've read Considerations for Seaworthiness several times, and skimmed it again, I cannot find the reference to beam vs wave height. Do you have a link to the actual study? From my understanding it is not possible to capsize a catamaran in non-breaking waves, only due to wind action on the structure or sails. My contemplation leads me to a design where the freeboard is very low so a large breaking wave would mostly flow over the hulls, basically minimizing the amount of water impacting the hull and thus imparted energy, and also immersing the windward hull preventing it from being tossed over, and minimizing sideways velocity and the likelihood of tripping. As far as the Anna catamaran, I read the articles you referenced, it sounds like they were one reef away from preventing a capsize.

    Mr. Efficiency. A large monohull, the queen mary, and a large catamaran are very different things, not comparable as far as I'm concerned.
     
  7. oldmulti
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    oldmulti Senior Member

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  8. guzzis3
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    guzzis3 Senior Member

    That got me laughing out loud.

    You should read the story on Richard Woods site about when they were overtaken by a hurricane. The cat was 9.9 meters I think. They got rescued but the boat was found later still afloat.

    Thomas Firth Jones also wrote about surviving hurricanes. Worth a read.

    Nothing in life is certain. People were convinced I'd die in a motorcycle crash. I've had worse injuries from rollerskating. Several cancers, 2 strokes, perforated bowel. No one will tell me anything I've done caused any of it. Just unlucky. When your numbers up you die.
     
  9. fallguy
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    fallguy Senior Member

    the natural state of the catamaran is upside down

    my answer, while provocative and humorous, is correct

    the only way to make a catamaran capsize proof would be for the bdeck to be underwater which has little practical use unless you want to call it a tri I suppose

    but there is quite a bit of good reading on the subject, this title is a bit off, but they touch on stability

    Determining Beam Width https://www.boatdesign.net/threads/determining-beam-width.56711/
     
  10. fallguy
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    fallguy Senior Member

  11. fallguy
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    fallguy Senior Member

  12. Mr Efficiency
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    Mr Efficiency Senior Member

    My understanding is that the US Navy was losing more ships to bad weather in the Pacific War at one stage, than enemy action, and the solution was to improve weather forecasting, not look for more seaworthy boats, my advice is take the tip, and avail yourself of the exceptionally good resources in weather and sea condition prediction available today, and steer clear of trouble. Just crazy to look at it otherwise.
     
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  13. comfisherman
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    comfisherman Junior Member

    Sometimes "that guy" is right.

    I fish in Alaska and have taken part in the push to exploit the 58 foot limit. While not catamaran, the probably come close. Several are 58x30 and 13feet deep. Driven by c32 cat mains, thick plate steel, pushed to the limits of men and machinery. Over built to levels almost comically so on all aspects, we still loose one ever few years.

    Building for worst case scenario has its point, avoiding the storm may have more validity.

    2019 a typhoon made landfall on the Alaska peninsula around wide bay. There were 3 idiots in that bay...... lost windows, vhf antenna, radoms, and an anemometer. Had both the Christian kid and the atheist praying.

    Replaced the electronics and ordered tougher 1/2 inch laminate windows for the wheel house.....old crab captain pointed out that better planning is better than overbuilding.
     
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