Multihull Collision Survivability

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

  1. buzzman
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    buzzman Senior Member

    Cmk2
    Good point...was forgetting when Rob went overboard. Doh.

    Agree. Rather be thought a fool than become one retrospectively.
     
  2. boradicus
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    boradicus Senior Member

    Yep. The same goes for land cruising on motorbikes. There are plenty of guys out there who will not wear helmets. I have always worn a helmet. Maybe I'm not cool with my helmet, but it sure saved my noggin when that pickup pulled out in front of me back in May of 2002 :D.
     
    Last edited: Jun 6, 2013
  3. buzzman
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    buzzman Senior Member

    Yeah, and the same idiots who won't wear life jackets are often the self same idiots who won't wear helmets....but still expect to be resuced,hospitalised, brought back to health, and/or looked after for life by the State, whose revenue...and the ability to meet the costs of these services...comes from our taxes...

    Perhaps off-shore vessels should be required to take out necessary 'survuval rescue' insurance that would compensate govts and other vessels for going out of their way to rescue those in distress?

    Of course, this might mean, as medical "insurance" in the US has showmn, that only those insured would be rescued, but it would allow those interested in or capable of self-rescue to reduce their insurance cost.

    Most people aren't aware that in motorcycle accidents, specifically 'single vehicle accidents', the rider is not covered by the (in NSW) compulsory Bodily Injury Insurance, for injuries sustained, although any pillion passenger is so covered.

    Perhaps we need some sort of compulsory insurance scheme for boats as well, the cost of which policy would depend on the type and survivability of the vessel (eg: floatation) and by the degree of expertise that could be demonstrated by the skipper.

    With maybe the provision of some paid for course that could be undertaken to improve one's skippering abilities.

    The current 'test' one is required to pass to get a motor-boat license is laughable, and there is no test whatsoever for sailboats.

    Never mind any test or examination to pass for offshore navigation or passage-making.

    And it will no doubt be the same people who insist that this should not be implemented as being in some way an infringement of "rights" they believe they hold or demand.
     
  4. boradicus
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    boradicus Senior Member

    Custom

    My impression is that maritime laws are customary in the same way that if you live in a farming community, if there is trouble in the neighborhood, people come out to help each other out. It is the community that looks out for each other because there it could easily be anyone from the community, and at sea, people are few and far between... Of course within coastal waters your proposal makes a good deal of sense if it is indeed the county or the coast guard that comes to the rescue.

    Anyway, Skint, what is the current status on your Kung Fu Catriman? The concept is actually fascinating.
     
  5. buzzman
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    buzzman Senior Member

    Whenever one of the single-handed racers is rescued by Australian naval or Coastguard vessels, usually after having been found by an Australian naval or Coastguard aircraft, there is inevitably a public outcry over the cost to the State (taxpayers) of such rescues, of usually foreign nationals, which can amount to hundreds of thousands of dollars.

    I concur that the custom (and indeed the International Law of the Sea) dictates that all vessels and nations must come to the aid of vessels in distress within their maritime 'sphere of influence'. It is probably that very 'international' nature that makes it impossible to implement what would need to be a global insurance scheme.

    But certainly, for inshore waters, from which the vast majority of rescues (and indeed deaths) are drawn, this ought to be within the bailiwick of each individual nation, and therefore something *could* be legislated.
     
  6. oldsailor7
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    oldsailor7 Senior Member

    Yes. A watertight panel accessible from the outside/inside above the waterline both upright and capsized. To enable the crew outside to get in---or out, depending on the circumstances.

    Also for consideration, a box or compartment with equipment/supplies in it which is accessible from both inside and outside, and which also would have to be in a suitable position.

    Some designers have shown cabin roofs or deckheads lined with as much as 150mm (6") of foam to float a capsized multi higher and make the wave swept wingdeck underside safer. This may have to be a trade off against extra windage or appearance.

    Air trapped in the upside down main hull is fine----for a while, but then there is the problem of getting fresh air in without losing the buoyancy of the trapped air.

    Underwing handles or rope loops to hang onto have also been advised.

    The undersides of hull seats/bunks may be arranged to enable dry occupation in the trapped air pocket of the upside down main hull, assuming that none of the through hull fittings were compromised allowing the trapped air to leak away.

    There must be lots of other ideas, pros and cons. :cool:
     
  7. cavalier mk2
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    cavalier mk2 Senior Member

    I think going retroactive would be better. Why legislate? Waivers would be better....in ancient times rescue wasn't a right, only a remote possibility and everyone gave seamanship their best shot. In this day and age the odds of rescue are a bit better but I've seen many deliberate breaches of the "rules" by tugs, freighters, powerboats and sailing craft and try to sail accordingly. Counting on these guys for rescue seems a bit optimistic at best. Now, a deck gun I'd stand in line for....
     
  8. buzzman
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    buzzman Senior Member

    Why restrict yourself to the coach roof? Why not put additional floatation foam over the entire deck surface as well..??

    Given the technique of infusion it should not matter for appearance, and the thickness of the foam sheet is irrelevant, whether 10mm or 50mm - or even 150mm - provided it was incorporated as part of the design.

    The diving bell technique could be used to re-pressurise and refresh the air in the hulls without breaching them.

    As for deck guns...to repel boarders?? With the rise of piracy in so many places around the globe this is almost becoming a necessity. I read about one good trick that was practised by the SoE on the 'Shetland Bus' run, where they used innocent looking fishing boats to run supplies and agents into occupied Norway during WWII (read book by David Howarth).

    The made a collapsible mounting for twin Lewis guns that folded inot a 44gall drum that was lined with concrete (for shielding) and popped up when the top was knocked off the drum. A tube attached to the underside of the lid below the drum opening was filled with oil, in case any inquisitive Quisling opened it and dipped a stick in - which apparently happened at least once. the join between the cut off top of the drum was hidden by ropes 'lashing' the drum to the bulwarks, although the drum itself was firmly bolted to the deck.

    Like to see one of those Somali speed boats faced with twin .303 Lewis guns, or even better, twin .50 cal Brownings.

    Not sure what you mean by waivers....??? Do you mean a way to avoid the insurance cost by agreeing *not* to be rescued and being self reliant...??
     
  9. MikeJohns
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    MikeJohns Senior Member

    But they are not good in the very sea conditions that turn them over. That's the problem I see, sure if they are blown over in fairly benign sea states

    Consider the 50 foot French Cat inverted recently in Scotland that was motoring not sailing with everyone ( 7 aboard) inside with the boat on autopilot, a sudden strong unexpected gust flipped the big Cat. Luckily they were in a benign sea state and were able to swim out in cold water and get on the upturned hull. Even then some of the people on board were close to hypothermia. They were unable to get back in to get the life raft or Epirb and it was late at night. Luckily an auto Epirb inside the hull triggered from the water ingress and they were rescued before anyone suffered too much. Had they had a life raft available they would have been warmer more comfortable and had some food and drink.

    Then consider another recent accident a similar sized Cat also French inverted by wave action in heavy weather in the Atlantic. All 5 people aboard drowned. There are numerous similar examples of people dying trying to stay on the upturned hull and being continually pounded by the waves until they are washed off and drowned and or die of exposure.

    Another Cat flipped here recently in the Great Australian Bight, it took them 4 hours of diving attempts to get the Epirb out of the hull, fortunately they had the life raft reasonably accessible, and once they operated the Epirb they were rescued from the life raft which they were occupying in preference to the upturned hull.
     
  10. MikeJohns
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    MikeJohns Senior Member

    The tremendous amount of reserve buoyancy in a monohull is a great safety factor. To preserve that we can easily bulkhead the craft. You say designers don't factor in enough floatation but for unlimited offshore survey we have to ! Then it can survive any one compartment breached (or swamped).

    It's just as easy to make a monohull ballasted sailboat as unsinkable as a multihull if you are bulkheading for damaged stability. And if you can design a multihull to be so equipped then so you can do the same for a monohull. It's just that you require an extra cubic meter of floatation for each ton of ballast over the non-ballasted craft. You can even do that with infatable bladders as you can in any craft.

    Where a thick foam hull would excell is with light construction where collision damage can be extensive like the whale encouter I mentioned that sank the Cat.
     
  11. buzzman
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    buzzman Senior Member

    MJ
    Yeah totally agree...the word is 'IF'......

    So for specific "naval architect designed for offshore survivability" a mono can be as buoyant as a multi....that has no extra thought go into it....

    Only problem is, most monos don't have any more 'purpose designed' floatation than a single hull of a multihull.

    So what if the forefoot has a collision bulkhead abaft the stem, and the compartment immediately behind it is filled with foam....and maybe the same at the opposite end of the boat.....

    In *mnost* production monos, in between is one long, inter-connected space *without* watertight bulkheads, which can fill with water.

    So maybe if the entire hull is built from 50mm foam...... or whatever...

    If you looked at that pic further up the thread of the tri with both bows of both amas torn off, and it was still afloat. Try doing that much damage to a mono..

    So obviously the tri was a bit too lightly built, but it *was* an older design, but with maybe a third of the inbuilt buoancy ripped off, the boat still floated.

    Doubt you could do the same with a mono...unless it was specifically designed to cope with that unlikely scenario.

    You don't need to do much to a multi to make it *super-safe* - just add a collision bulkhead and solid foam in the ends. Even if one float gets torn right off, the rest will probably still float, after a fashion.

    The biggest issue in the multi VS mono debate is that monos can be rolled right over and potentiuall still sail away, even if they require a jury rig.

    But roll a multi right over and it's going nowhere without external assistance.

    So although it might be a relatively nice place to be, compared to a mono, you are dependent on the currents and the possibility of a ship being able to assist you to flip the boat.

    If someone can definitely design a method of multi-hull self-recovery, I still maintain it will virtually make monos unnecessary, as that is really the only advantage they have over multis.
     
  12. MikeJohns
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    MikeJohns Senior Member

    I don't agree. There's a huge amount that we could discuss about this. They are very different craft that have quite different characteristics advantages and disadvantages. But lets keep this about collision survivability of multihulls and discuss this on another thread perhaps.
     
  13. buzzman
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    buzzman Senior Member

    LOL.....you're right, of course...horses for courses.

    Don't let my 'partiality' get in the way. :)

    They are both quite different types of vessel and, as you say, have both good and bad points...depending on the use to which they will be put, and the conditions under which they'll operate.
     
  14. boradicus
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    boradicus Senior Member

    Motorsailing?

    Could it be that in the first instance they were sailing with the motor? Otherwise I don't know how a gust would topple them - isn't that a no no? In the other instance, I am wondering about the specific type of cat - both of these were of French make and a similar size.... which makes me wonder if there is some design flaw similarity between the two that predisposed them as such to capsize...

    Just some thoughts - more data would be good, of course - especially if it turns out to be relevant to people who would want to avoid purchasing cats of that cloth (assuming that there was some common design consideration that presented a similar factor for determination of the capsizability).

    The ability to be capsized is also a factor of survivability with relation to the topic of the thread, but I am not sure how this particularly relates to the design that Skint proposed or what stage the planning process for that design is in at present.

    Thanks :)
     

  15. cavalier mk2
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    cavalier mk2 Senior Member

    Yes Mike we'll have to agree to disagree. Multihulls and monos aren't safer than the other, both depend upon good design, outfitting and operation. Silly examples, the overall track record of cruising multihulls is quite good even if not maximized for safety. The boats you chose are BAD, not what I suggested. Many more monos through design, construction and outfitting come to grief, of course this is because there are more of them. All boats need to be well found for the use they are subjected to.
     
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