Multihull Collision Survivability

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

  1. cavalier mk2
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    cavalier mk2 Senior Member

    The book shows pulling stern over flooded bow, the idea being less water resistance with the pointy ends though it is possible either way. Each design needs to be sized up for flotation and flooding possibilities to determine the method.. A para sail might be a great way to get pull or push.
     
  2. buzzman
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    buzzman Senior Member

    I'm sure I saw the bow-over-stern somewhere - maybe it was on YouTube...???

    The para anchor idea I agree might be good, especially as it is something every *cautious* off-shore multihuller should carry.

    To extend the idea to the full capsize: if sockets could be built into the hull, perhaps at a 45deg angle to the vertical, aimed outboard, and if two could be provided equidistant from the centreline of weight transfer (or whatever engineers call it), then a couple of oars or spinnaker poles could be slotted and used as sheer legs to raise the para anchor full of water outboard of the hull.

    Probably you'd need much longer sheer legs and a much larger container than a para anchor - I can't do the maths being an ignoramus in such fields, but it might be worth investigating.

    Perhaps more so for tris, as multiple additional 'overturning masses' could be added to the outer and main hull, say to the leeward side of drift and perhaps by also using the swell simultaneously it might be possible to flip a capsized tri....

    Might, being the operative word.

    But it ought to be possible to add in at design/construction phase on a tri sufficient watertight compartments that could be flooded to upset the inherent floatation balance when inverted.

    They might need seacocks in the side of the hull and perhaps on the keel line, to allow air to escape as the compartments fill from below. (Via deck-mounted openings or seacocks)

    There is also some speculation on Farrier's site about the ability to flip a tri with folding akas by folding the leeward one in, but I suspect that would still not be enough to counterbalance the mass (and drag) afforded by the rig.

    It might be sensible for 'off-shore' tris to feature a loose-footed main, such that it could be easily detached at the boom to reduce drag while attempting to write the boat by rotating around it's longitudinal axis. Only the mast and rigging would then create any real drag.

    I suspect the reason most theories focus on righting by rotating around the transverse centreline axis are precisely to reduce this drag, and hence why bow over stern makes more sense, as the boom and main would naturally stream aft, providing minimal resistance.

    No doubt one day some seriously talented hydrodynamic engineer will put fingers to keyboard and calculate the forces applying.....

    ...after which, designers will be able to implement mods such as those above with some degree of certainty of success.
     
  3. HASYB
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    HASYB Senior Member

    Len Surtees has designed a rightable trimaran.

    http://www.surteesmultihulls.com/11m-re-rightable-trimaran.php


    A bit more on the matter of seakeeping abilities of a trimaran in a storm recently by Ian Farrier in a thread on SA:

    It is always better to keep moving if one can, as the multihull's speed can also be a big safety factor. But sometimes one wants to go where the wind is coming from, which is why I laid ahull off the South Island of New Zealand, as it was a north west gale and I wanted to go north. Tried beating into it for a while, heavily reefed, but all I got was a heavy beating. So took everything down and laid ahull while cooking lunch. It was something I had wanted to try since hearing how Nigel Tetley used it all the time while rounding Cape Horn in his 40' tri 'Victress' (the first tri to so so). Suitably impressed, I stayed that way for around 6 hours as I recall, and since that time I have always taken particular care to design in the ability to lay ahull (floats need to be receptive for surfing sideways).

    However, the moment the wind changed to south west it was off again at 10 - 14 knots heading north, with full sail! Seas were confused, but the boat could take it, and my speed meant I got to the nearest harbor (Port Underwood) before the worst of the wind arrived (built up to 80 knots). A monohull nearby was not so lucky and had to spend the night heaved to in Cook Strait (no lights in Port Underwood at the time). It was scary enough for me going in right at night fall, but I certainly did not want to spend the night in Cook Strait. Went in for 1.8 miles as I recall on a compass bearing (pitch black), turned right until I saw the rocks, and then dropped anchor. Luckily it held. When I woke up next day the monohull was just coming in and we anchored together further up the harbor, while the wind blew solidly for two days. His boat was being laid flat in the gusts so he spent a fair bit of time on my boat.....

    Ian Farrier

    Farrier Marine
    Designs That Work


    Ian,

    Sure would like to hear more details about your lying ahull. Did you have your rudder hard over? No risk of rudder damage? Were the waves on the beam? Thanks!

    Just took all sail down and left the boat to look after itself. The natural position in this situation is for the boat to lay beam on to the waves and just go up and over them sideways. Occasionally a big one would break and hit the boat, but all it did was accelerate and surf sideways, at which time one just had to hang on. Seemed to handle it all quite safely, which is good advantage for the wide beam trimaran.

    The rudder was down, as it was not retractable, but it was only a low aspect rudder (and a strong one), so no real drag. If it had been retractable then I would have pulled it up. Can't remember how it was tied, but would guess it was, and likely hard over to turn bows into the wind. But it really had no effect that I can recall. No daggerboard either, just small fins on the floats, so there was nothing much to stop it surfing sideways.

    The only scary part was when it went over the top of a big wave sideways, where main hull would teeter on the crest, and then it would fall into the trough behind with a huge boom and the whole boat would shudder. But it was mostly noise, the boat seemed to handle it okay, and overall I felt quite safe. Heaving too with a well reefed main, backwinded storm jib, and rudder hard over, is probably more comfortable, as the boat is more bow into the waves, but I did want to try the basic laying a hull, and I found it worked as well as Nigel Tetley said it did with his Victress.

    Ian Farrier

    Farrier Marine
    Designs that work


    I'm not a big fan of drogues, and did not have one on board, as they don't work well other than in slowing one down when running before big seas, which is their only real use. I did however have a sea parachute on board, and these do work by holding the boat bow on, unlike a drogue. However, the conditions never got to a state where I thought it was needed. Next day, it may have become necessary (80 knots), but then my speed while running before had got me to a harbour well before it got too bad. Speed is safety.

    Holding a boat in the water can also be very bad for a lightweight multihull, as its safety depends on it being light and able to go up and over, or shoot sideways or whatever out of the way of a breaking wave. Just like a ping pong ball. Trying to hold it in place by a drogue or parachute can be dangerous, unless properly bow on (which a drogue will not do) and at the end of a long springy nylon line. Think 'dance like a butterfly' and the waves will find it hard to get hold of you.

    I also later laid ahull in a heavy 38' keelboat, while sailing to Tonga, and that was a nightmare in comparison. It was heavy and locked in the water by its keel, and it seemed every wave was trying to pound the '!&#$@$' out of us. Monohulls have to be built super strong because of this, which then makes it even worse. Plus of course it was rolling from gunwale to gunwale, and this was probably the most uncomfortable night I have ever spent at sea. There was no way any cooking could have been done as I was able to do on the tri while ahull. Completely sold me on the advantages of a good trimaran.

    Ian Farrier

    Farrier Marine
    Designs that work
     
  4. HASYB
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    HASYB Senior Member

  5. buzzman
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    buzzman Senior Member

    He doesn't say *how* it was "self-righted" - but the relatively calm waters of San Diego Bay might not bear comparison to the mid-Pacific during a gale.

    I'm not too keen on the fixed keels and rudders of the Surtees design. As Ian Farrier states in his comments, the tri needs to be able to 'skid' sideways with daggers/keels and rudders *up* if at all possible.

    Jim Brown said much the same thing in his book the Case for the Cruising Trimaran.

    And there seems to be general agrement with what Ian said about drogues and parachutes - the former useful to help you slow down while running off before a gale; the latter useful to keep the craft head to wind while drifting under bare poles in conditions where running off is no longer possible.

    And while Ian is correct to say that speed is safety - this is more true for coastal sailors than deep-ocean. Out there, there is nowhere to run......

    But it is certainly true that a multis speed advantage helps to 'broaden' weather windows making longer passages possible than in a comparable mono in between forecast weather events.....

    Six of one, half a dozen of the other.

    But the point the mono enthusiasts continue to point to as the only *real* failing of the multis is the lack of ability to 'self-right' in the way a keeled mono does.

    Plenty of stories about monos being rolled over to 160deg or even 360deg, with the mass of the keel eventually counterbalancing the hull and popping the rig back upright.

    Under that definition of "self-righting" even the Surtees design *fails* the test.

    And I doubt that bridge will ever be crossed.

    Hadn't seen that particular vid before - the one I think I saw was older and a smaller boat, and was an 'experiment' not a real life situation - but that F31 indicates at least that bow over stern is possible.....with external assistance!

    And that is the key to the mono guys arguments - no 'assistance' out there mid ocean - so better to be slower, and roll more, and have to carry an expensive liferaft, and not be able to cook in bad weather, and be knocked down frequently, rather than run the risk of maybe toppling over and completely inverting the multi and being unable to 'self-recover'.

    Whoever can solve this dilemma will probably kill off monohulls for good, as recent experience with the Americas Cup has shown.

    Why sail a mono when you can sail a multi...???? ;)
     
  6. cavalier mk2
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    cavalier mk2 Senior Member

    The righting theories are well covered in the book , "The Capsize Bugaboo", the bow flood righting was propositioned for cats originally by a Mr. Ruiz and was demonstrated at the 1976 multihull symposium. Paddy (old Sailor 7) was a sponsor and might have watched the demonstration? In the book a Newick Tremelino is shown using the stern variation. For sure having a means to haul sails down (if still up) while inverted would be a help.
     
  7. cavalier mk2
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    cavalier mk2 Senior Member

    I'm not sure multihulls need to self recover. They need to take care of you while inverted and offer the opportunity to right when the weather is settled. Most do a good job of taking care of the sailor in the first place.
     
  8. buzzman
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    buzzman Senior Member

    Oh! That's one I haven't read yet. Must track it down.

    Think you're right - think the name Ruiz rings a bell, so maybe I've seen the pics from that demo posted on a forum somewhere..??

    Seems to me that bow over stern wouldn't require the sails to be lowered, just the sheets cast off to allow them to flop around...?
     
  9. cavalier mk2
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    cavalier mk2 Senior Member

    That is what the tremelino did, however for some boats the other way is easier plus having sails up with flooded hulls is inviting another inversion. Harris has some interesting ideas involving propulsion and ama flooding. Hydraulic drives with a rotating inboard have interesting possibilities too but it is the simple things that tend to work.
     
  10. buzzman
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    buzzman Senior Member

    CMk2

    I tend to agree...and this is the case Jim Brown argues....for making the storm survivable for the sailor by keeping the boat afloat, whereas a flooded mono goes straight down.

    My comment about *fixing* the "self-righting" problem was purely from the point of view of being able to thumb our collective nose at the mono guys.... :)

    But, accepting that 'survivability' is a useful feature of multis still requires them to be "self-recoverable" (note change of emphasis).

    Which is what Jim argues, and which I am am merely parroting.....

    Have had a few thoughts on the subject though. One of which, based on something similar in Jim's book, was the idea of having a closable (latched) compartment on the underside of the wing, containing a bottle or two of water and a some iron rations - glucose etc, plus a small saw like those Japanase push-pull saws to enable the crew to cut their way back into the hull.

    One thing have noticed in cat construction, especially the modern palazzos, is that the windows and doors to the bridge deck are not usually sealable - not in the way hatches and portholes are, which means a capsized cat cannot be made watertight from the inside.

    A tri with a sliding companion hatch in the coachroof probably has the same problem. Once you cut your way back inside - and thus relase the pressurised air that was partially responsible for keeping the boat afloat - you must end up swimming or at least wading around inside the hull/hulls.

    If the companion door/bridgedeck windows could be re-sealed like deck hatches once you've got back inside the boat, then the existing bilge pump could be reversed and the hull pumped dry-ish.

    So the bilge pump installation should allow for it to be demounted and turned up the other way, and the hoses re-routed (ie: not epoxied or screwed off), so that once inside it was relatively simple to reverse the location of the pump.

    Once the interior was dry-ish it would be a lot more habitable and easier to maintain a survival state than clinging to the underside of an upturned cat.

    There is a vid of two guys who did the latter and were rescued by a freighter on the web somewhere, filmed from the freighter.

    I wondered since why they didn't get the freighter to try to tow them over, especially as the cat was noticeably down in the stern.

    The issue for cats is that while the hulls stay (relatively) above water, the entire bridgedeck is underwater, and cutting into either of the hulls - and thus releasing the pent up pressure (and consequent additional floatation) could only make matters worse.

    A trimaran is thus potentially a better survivability option in a capsize than a cat, which I think Jim also argued.

    I have been attempting to design a watertight shutter for the inside of a companionway which does not have a sliding overhead portion. Rather, the companion will be located in an aft cabin bulkhead sloped at 45deg(-ish) with a door that opens inwards for 'normal' operations, but with an additional 'dish-shaped *shutter* which can be tightly sealed over the whole shebang once the crew is back inside the hull.

    Probably using the type of screw fittings used in steel commercial boats watertight doors. With wingnuts on a threaded bolt that slots into a 'keyhole' in a fitting permanently and firmly fixed to the inside of the bulkhead, so that once clipped into the keyholes on the bulkhead they could be clipped into slots in a metal fitting on the sides of the inverted 'dish-shaped shutter' and then screwd down tight to pull the shutter against a seal glued to the inside of the bulkhead.

    This shutter could sit inside a seat compartment or up under the cockpit foor where it could be easily reached after an inversion.
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    Either a cat or tri can be made habitable if properly prepared but one thing that has killed people is not having fresh air. If you don't have a supply of fresh air your time is limited. In a cat or tri buoyancy chambers should float a living space that can stay dry(ish) while vented.
     
  12. buzzman
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    buzzman Senior Member

    Yes, I agree. "Habitable".

    But *how* habitable???

    A bridgedeck cat would probably float with the underside of the bridgedeck awash or only just above the surface, meaning that all the living space in the bridgedeck would be unavailable, and as the openings into the two hulls would, ipso facto, allow water to flow from the bridgedeck area down into them, at best a cat sailor would be up to their knees.

    Similarly, a tri with an unsealable companionway would tend to float with the above deck portion of the coach house under water at least, so again, a tri sailor would probably be at best ankle deep, but as the boat lifts and falls on the waves, so too would the water inside the hull surge back and forth.

    Hence my idea for sealing the inside of the companionway with a watertight shutter.

    If cat builders utilised hatch-type sealable windows and doors to the bridgedeck, rather than the sliding patio doors with which so many of them seem to be fitted, then cat sailors in extremis may also have the option of utilising more of the boat.

    Keeping dry and avoiding hypothermia are the keys to survival, and this necessitates dry clothes and skin - which is tricky if you're sharing a hull with part of the ocean.

    And I am only parrotting what Jim Brown has already argued in his book.

    All I have done is think about how it might be made more watertight and thus *more* habitable.
     
  13. HASYB
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    HASYB Senior Member

    I'm all in favor of getting lots of information about the subject and learn. I just don't understand the eternal quarrel between mono and multihull so don't think there is a dilemma to be solved if there is one :rolleyes:; it just adds nothing to the understanding IMHO. They're different; so what. Both have their specifics.

    Back to some more info.
    In the links the story of Tahiti Belle. I visited Nic Barham and inspected the boat, as I was searching for a winged Val, in the winter before the boat was lost in the atlantic on her way back in the 2008 Jester. He actually wanted to sell the trimaran and do the Jester in a smaller mono :rolleyes: as he thought the tri had become too "nippy" for him. I found the boat too expensive then and also had an awkward feeling something was wrong; which I didn't tell Nic. Still feel kind of strangely responsible/sorry the boat was lost but thankfully Nic survived.

    http://www.soundingsonline.com/features/in-depth/237642-what-i-learned-on-tahiti-belle

    http://www.soundingsonline.com/features/in-depth/237742-for-want-of-a-drogue-
     

    Attached Files:

  14. Delane
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    Delane Senior Member

    PET Bottles 4 Flotation

    When I built my new appendage to the bottom of my J-24 Tri, I used pressurized PET bottles and stuffed as many as possible into 5 sealed off sections. I first put the bottles in the freezer for 30 minutes or so and upon opening the door I placed the caps back on the bottles before pulling them out. Ambient room temp pressurized the bottles really tight. I have over 200 bottles in the appendage and foam in the front end section. It would be really hard for any 1 section to take on much water in a collision.
     

  15. buzzman
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    buzzman Senior Member

    I think the basis of the "mono vs multi" *debate* comes down to "tradition" and, dare I say it, plain envy on one side, and naturally defensive pragmatical stubborness on the other.

    The mono guys don't like the fact that multis are faster, so exclude them from most races, thus limiting their popularity to 'multi-only' racing. The AC has only recently allowed multis and what was the result? All are now multis, as a mono can't compete, as Denis Connor conclusively proved against New Zealand.

    There are some "traditionalists" who decry all multis as 'not proper sail boats' - ie: a sailboat has to have one hull, as they *always* have done.

    Such people are reluctant to acknowledge the oceangoing craft of the Melanesians and Polynesians and the inshore fishing craft of southern India, from which the name 'kattu marran' comes. According to one website this is a Tamil word for 'bound logs', apparently.

    And the non-self-righting capabilities of multis are (arguably correctly) derided as inherently *unsafe* by the mono guys.

    The counter argument is that multis are faster, heel less, are more comfortable, have greater accommodation for length, remain afloat even when holed and are VERY hard to sink - unlike the monos with their massive lead keel weights.

    And they love to point out how much more multis cost to berth in a marina.

    Horses for courses.

    I suspect that if the folding aka tris like Farriers and Quornings can be proven to be "self-recoverable" after an inversion, then monos will probably become unnecessary, as they could then counter all but the 'traditional' argument which, in the end, comes down to personal taste.

    But faster, more accommodating, no wider in a marina, *and* self-recoverable..?? What's not to like?

    For the truly tragic they could even be carvel-planked in sold timber, or perhaps strip-planked, if there is still an insistance for 'all timber' construction. ;)

    Fascinating story from Nic Barham, and the pics are interesting too but I did notice a couple of things he left off his "what I learned" list:

    1. - a sextant and the ability to use it, plus usable maps: electronics can fail, batteries can go flat, motors not start (no generator), and solar panels can be immersed and useless (after an inversion) or ripped off by waves.

    No point having a battery-operated VHF to talk to SAR if you don't know where you are. Might as well have neither and be self-recoverable....

    2. - floatation foam in the amas: okay, accepted that the Val Nic sailed was older, so probably didn't have that option at build time, but even smaller pieces of styrofoam added to such floatation compartments (in order to fill as many gaps as possible) and then resealed might have meant the Val was still sailable, even if one or more of the float ends was ripped off. Ditto for the wing decks on fixed wing tris.

    3. - he acknowledges he went to sea without a rope for the drogue he had on board. An almost fatal mistake, perhaps, but certainly a drogue and a para anchor should be as essential as a lifejacket with a crotch strap on any multi offshore.

    From the pics on the site, it appeared that the front third of both amas had broken off at the wing-deck join, so clearly this is a join which should have been made significantly stronger. Again, it's an older boat, and designers have learned a lot, especially about laminating and strengthening weak points since then.

    It is arguable that, had the floatation compartments been solid foam inside the ply skin, whether that additional strength might not have helped prevent the damage that occurred.

    And finally, the point ought to be made that much of Nic's list of what he considered essential were electronics and other equipment to aid a rescuer.

    As many have argued over the years, sailors heading offshore *ought* to be self-contained and capable of self-recovery, except perhaps in the case of acute medical emergency such as a stroke or compound fracture of the leg, for example, especially on non-solo voyages.

    And what do you do if you press the EPIRB button...and no-one comes.. as happened at least once not too many years ago in a hurricane in the Indian Ocean when a couple of experienced sailors in a mono were lost.

    There are numerous cases of people being 'rescued' from boats that didn't actually sink, and were eventually cast ashore in a relatively sailable condition.

    One such mono recently came ashore on the east coast of Australia after having been abandoned by its couple crew mid-Pacific. It was going to cost them thousands to dig the boat out of the beach and haul it onto a low-loader.

    Clearly from the evidence (it made it to Australia without sinking) it could have been sailed into the nearest port had the crew not abandoned it.

    To me this sort of episode smacks of the wider societal malaise of irresponsibility - and I mean that purely in the sense of "lack of personal responsibility for one's actions" that seems to have taken a general hold worldwide.

    Someone else is always to blame - not oneself.

    In the case of misadventure, it is assumed, if not actually demanded, that *authorities* come to the rescue of the foolish.

    It is heartening (if not at times harrowing) to read the adventures of the pre-electronics generations of sailors, who had no choice but to self-recover.

    Whether it was Cook's Endeavour, holed on the Reef, throwing overboard everything that was heavy in order to reduce the draught and thus the pressure on the fothering mats, to reduce the inflow until the ship could be careened and repaired, all hands pumping continuously day and night.

    Or like David Lewis, twice dismasted in Rehu Moana on its 'shakedown' cruise to Iceland, and later, thrice rolled completely over in the Southern Ocean in Icebird while attempting the first solo circumnavigation of Antarctica....

    Or Frank Dye, twice capsized in the 16ft Wayfarer dinghy he sailed from Scotland to Iceland and Norway....

    Or Webb Chiles, swamped and capsized a number of times in his 18ft Drascombe lugger Chidiock Tichbourne while attempting the first ever circumnavigation in an open boat. Needless to say he abandoned that effort a quarter of the way round, but essentially proved it was theoretically possible....

    All of whom had no choice but to manage their adventures and in the event of a mis-adventure, to self-recover and figure out a way to get back to port.

    Perhaps it's time sailors attempting dangerous activities (ie: sailing, especially offshore) once again accepted personal responsibility for their actions.

    I note that the other 'peak' adventure sport (pun intended) of climbing Everest has now become more like a very slow, very cold, funeral procession, in which the body is simply left on the side of the mountain.

    OK, accepted, it's not a fair comparison, as all who do the climb are part of teams, but Lincoln Hall's remarkable rescue after being left for dead was the exception that proves the rule.

    It seems to me, at least, that EPIRB use should be restricted to non-survivable catastrophe or an actual sinking, rather than engaged simply because the sails have ripped and the missus wants to go home....

    And if some SAR expert panel decides that an EPIRB was set off in a 'survivable' situation (like the couple whose boat came ashore in Australia) they should be liable for the cost to the rest of the community of that rescue.

    The subsequent 3rd party insurance costs for 'race organisers' like the BOC might then make such events unviable. No loss from my perspective, but if the option of not having the race, or being entirely self-sufficient was offered to participants, some would no doubt still accept the challenge.

    And prepare accordingly....



    EDIT: Emails crossed in the ether...the idea of placing PET bottles in the freezer is an excellent one, and any floatation added is better than none at all, but solid, carved-to-hull-shape extruded styrofoam seems to be the ideal solution, incorporated at build or refurb time.

    Another useful and not too expensive readily available alt.floatation is the foam sausages called 'swimming pool noodles' used in domestic swimming pools for fun, but available in bulk from wholesalers reasonable cost effectively. These can be shoved up into crevices as well as used to 'fill' floatation chambers and being made from EVA foam are 95% as good as extruded polystyrene, but with the addition of flexibility, so they conform to hull curves and need no (or only minimal) shaping or carving to shape. I'm using these to add permanent floatation to the "floatation chambers" on a 14ft dinghy as these now leak, and the only access (without carving a hole in the fibreglass chamber) is via 4" inspection hole, through which the noodles will fit.
     
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