Multihull Collision Survivability

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

  1. redreuben
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    redreuben redreuben

    Those large 20-25l bottles from water dispensers would work well with smaller ones to infill.
     
  2. cavalier mk2
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    cavalier mk2 Senior Member

    They'd never fit in my wings, The access ports are 5-6 inches. I use more rectangular bottles for less gaps but the neat thing over spray in foam is they allow good air circulation for rot prevention ans are removable for maintenance or to change the floating characteristics of the boat.
     
  3. buzzman
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    buzzman Senior Member

    Might not such bottles rupture in a collision or sever impact?

    Try stepping on a milk bottle with it's lid screwd on.....

    Nice idea and cheap.....but would not proper buoyancy foam glassed in be the 'best' solution?

    And of the possible foams, would not EPP be 'better' able to resist impact as it is deformable, whereas styrofoam is not?

    So in the event of a hull rupture, the EPP would be less likely to shift or fall out, especially if it was glassed in or epoxied to the hull...???

    I seek information, not controversy... :)
     
  4. redreuben
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    redreuben redreuben

    Buzz,
    Foam plus glass =weight so less buoyancy. One or two bottles may rupture but not all. Glueing the lids on helps here. And as mentioned removable for maintenance. In timber hulls glassed in foam is a rot trap.
     
  5. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

    What are acid bags?
     
  6. oldsailor7
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    oldsailor7 Senior Member

    They are tough, flexible plastic bags, rectangular in shape, made specially to withstand puncture and about 4-5 Litres in capacity. They are used for delivering the hydrochloric acid used by battery makers.
    They can be crumpled up to put in position, then inflated with a domestic vacuum cleaner. The pressure is left to equalize before screwing on the caps.
     
  7. masalai
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    masalai masalai

    I heard of this whilst I was travelling north - Did not realise it was the local Volunteer Coastguard doing some "whale watching" in Hervey Bay... I think I was behind Frazer Island at Kingfisher Bay resort, (half way along Sandy Strait), having lunch...

    In whale watching season I drag my 'rubber-duckie' and get visits from other whales with their babies come over to inspect my "baby"... I cut my engines, get a good view as they both circle my boat then depart leaving me in peace to resume my way north...

    I do not have "filling" but 16 sealed voids and three-layers on the bottom (a solid 300mm wide flat shoe sole), made of:- from the top - 400gsm plus tapes / end grain balsa (19mm) / 400gsm GRP / layups of quad-axial GRP / 9mm marine-ply / layups of more quad-axial GRP then the mini-keels made of 9mm ply covered with grp inside and out and designed to take the load of a grounding and frontal bump with no problems...
     
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  8. MikeJohns
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    MikeJohns Senior Member

    Brian

    Collision with whales is becoming more common on our coast now. they can be hard to see and invariably cause more damage than you'd expect.

    I hit a sunfish on the way south from Sydney in Dec! It scraped right down the side of the boat and a wave lifted its fin up to the wheelhouse window level as it went past.

    I thought then of the lost keels and rudders just from these fish, Whales are more likely to be hit than containers and do just a much damage.

    One emergency floatation method is to inflate a life raft in the holed compartment.
     
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  9. masalai
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    masalai masalai

    I forgot to mention, I had one mother and child encounter half way between Urangan and Bundaberg going north (2 days after that 'collision' happened) and off the Wide Bay Bar having just cleared the outside way-point on my way south...

    There was quite a slick in the area and she must have given birth minutes before and felt that if I did not have a "calf in tow", I would have felt the protective wrath of a new mother... I stopped totally - even killing the engines, - She came close to the rubber-duckie, circled me slowly and carefully then continued north... I headed south to anchor up overnight in the lee of Double Island Point...

    Usually, when cruising I watch the tides, and when the flow is against me I travel fairly close to the beach, (beyond the breaking seas - I draw 3 ft), otherwise take advantage of the tidal flow and swell to go with the flow... The abindance of little rocky outcrops in that region has me quite paranoid in keeping a very careful watch on where I am going and what information is on the charts...
     
  10. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

    Where do you get acid bags?
     
  11. oldsailor7
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    oldsailor7 Senior Member

    Sorry IN.
    I really don't know, as I have never tried to source them here in Aus.
    Try the Yellow Pages.
     
  12. masalai
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    masalai masalai

    Or a car/truck lead/acid type battery wholesaler/manufacturer...
     
  13. Alive
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    Alive New Member

    @whitwpointer23, I agree polyethylene is amazing. When my Windrider17 trimaran got flipped by a storm, when on a mooring at low tide, it crashed upside into in the mud so hard one of the ama's got a severe bend and crease in the last 1m of bow of around 30 degrees off straight. Amazingly it slowly straightened out by itself and now with no repair work you can't even see that it was ever damaged!

    I have also sailed into various rocks etc and the hulls just bounce off, so I am very happy with the WR17 for close shore sailing.

    However polyethylene is very difficult to bond to other materials and works best when rotomolded in one piece, so it is probably not very useful for larger boats.

    Foam core construction with sealed bow bulkheads would be the best compromise.
     
  14. boradicus
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    boradicus Senior Member

    That is a cool idea! I was just thinking that if you happened to pitch pole a cat or a tri that if you had some inflatable bags, and inflatable dinghy, and a way to separate the hulls temporarily and reattach them, that you could use the air bags to even right the vessel section by section...
     

  15. buzzman
    Joined: May 2011
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    buzzman Senior Member

    Not a good idea. Separating the hulls is a no-no even if it was possible, which on most cats and tris it isn't.

    What might make more sense would be a horizontal tube fitting, side to side across the centre of the deck (like the socket for a prodder on a skiff).

    A Cat on its beam end, with windward hull aloft might then be overbalanced by slotting a spinnaker pole into the socket and winching a large parachute anchor full of water up to it.

    Obviously, have to tie off the vent in the para if there is one.

    The idea being that the mass of water (ie: weight) would overbalance the upward hull, pulling it back down into the water and thus popping the sunken hull back up to water level.

    However cats don't tend to stay upright for long and usually end up face down, capsized.

    The only proven way to right a capsized cat is to tow it end over end - the reverse of a pitchpole - using external assistance, like a power boat. Pulling it sideways over can rip the mast and rig off, apparently.

    This is why they are not favoured for deep ocean voyages, as once they are flipped, you are buggered.

    But, as we love to point out to the monohull brigade, still afloat - on a very large 'raft' - so an EPIRB is a must have for multi-hull sailors.

    Whereas a capsized mono has an alarming tendency to fill with water and, due to the mass of its lead keel, quickly sink to the bottom.

    Which is why monohulls offshore should always carry an (expensive) emergency life raft.

    Multihulls are their own liferaft.

    Jim Brown offers good arguments for the safety of multis in his 'Case for the Cruising Trimaran'.

    He also points out that there have been *experiments* undertaken to right tris end over end by filling the aft end of the hulls with water to make them sink, and pulling the bow over the centre.

    The catch is finding someone who can provide the pull - unless you can harness a passing whale...??
     
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