Lining with closed-cell foam for floatation, insulation, and safety

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  • 02 Dec 2019 08:09
    Reply # 8152614 on 8148577

    Good sense talked by both Graeme and David. Unsinkability on a ballasted monohull by filling with foam is something that sounds like a good idea in theory, but one that can only be achieved by sacrificing  everything that makes the boat useful - stowage space etc. Better to concentrate on eliminating the causes of sinking: through hulls and insecure washboards, mainly. When I first started ocean sailing, and was 1000 miles from anywhere, I was forever thinking "there's only 18mm of plywood between me and the vastness of the ocean". You just have to get over that way of thinking.

    By all means put in watertight bulkheads fore and aft, with absolutely bomb-proof hatches through them so that they can still be used for stowage. You might be able to achieve the necessary cubic metre or more of enclosed air that way. Watertight bulkheads would be very much in the Chinese tradition.

    Foam for insulation in a GRP boat is another matter, and much to be desired. For a boat used in the warmer months, closed cell foam of the camping mat kind, 10mm thick, bonded to the inside of the topsides and deck, will be enough. For a boat that is to be lived on in winter, with heat to be generated and kept inside, up to 50mm of foam is good. I did that on Tystie, and was glad of it in the winter.

  • 02 Dec 2019 06:23
    Reply # 8151854 on 8148577

    Chris has just pointed out to me (very tactfully off-forum) that car airbags won't work because they are perforated and intended to immediately deflate.

    I pulled the ripcord on an old well out-of-service liferaft once, just to see what would happen. Something happened all right. The raft came apart at the seams and the perished bottom fell apart. But the infllatable ring popped up in a seriously impressive manner, and stayed up. If that had happened inside a small cabin (with the crew on the side nearest the hatch!) I reckon you would have some instant flotation. I have found with CO2 extinguishers too, the gas seems to last and hold its pressure for many many years.

    Perhaps some other inflatable bladder(s) of some kind and a bottle of gas - or even an old liferaft out of its case -  could be stowed up forward as a source of instant emergency buoyancy. Its just a thought.

    Last modified: 02 Dec 2019 06:25 | Anonymous member
  • 02 Dec 2019 04:41
    Reply # 8151154 on 8148577

    Well, I would have to concur with Graeme's thoughts. Although it would be very nice to have an unsinkable boat I think it is one of the risks we accept when going to sea. The solution to a potentially sinkable boat when going offshore is a life raft, if you believe in such things. Actually I think the biggest, no escape from, risk to any cruising boat is an out of control fire at sea. Even unsinkability is not going to save you from that. So as with driving a car, or flying, there are risks that I think we just need to accept as part of the fun.

    Now insulating with foam is something I do agree with. On one of my yachts I insulated the deckhead with 20mm thick sheets of polystyrene covered with an off-white vinyl. The panels were a friction fit between the deck stringers. It looked attractive, helped reduce condensation, was so light weight as to almost not be there. But the boat was a plywood trimaran so I did not need to worry about flotation! I did something like 15 ocean crossings in that trimaran. Although the boat was probably unsinkable there was always the potential of capsize at sea. My solution to this was planning, good preparation, and good seamanship.

    Last modified: 02 Dec 2019 04:50 | Anonymous member
  • 02 Dec 2019 02:44
    Reply # 8150297 on 8148577

    I loved the youtube clips you have done, especially the mini-junket with Emmelene and Amiina (    )

    Here are some thoughts straight off the top of my (somewhat aged and feeble) head, on your flotation proposal, maybe a bit ignorant but then again, maybe will provoke further discussion:

    The idea of gutting the boat, and lining it with foam, surfacing the foam and then re-assembling seems a huge undertaking especially for someone who is not 100% well, for the only immediate benefit that I can see, of improved insulation. As you point out yourself, the best you get from that if you ever sink at sea, will be a nearly submerged boat which will be impossible to pump out and probably not much more visible to a rescue party than you would be just floating in a life jacket. Personally (and I am currently in a similar position, with just a tiny boat to cruise in at present, and nowhere near as fit and agile as I used to be) I would rather spend the time enjoyably sailing, and just try to avoid sinking at sea.

    The biggest danger to your life is probably driving your car to the boat and back, perhaps putting your trust in an airbag, which – I’ll come to that later.

    You can survive at sea in a partially submerged boat – the amazing story of the Rose Noelle in which 4 men survived 119 days at sea in a capsized trimaran is an example – but the hulk was floating sufficiently high that, even upside-down, it provided a habitable haven in which the men could survive. A monohull awash, barely floating and quite possibly upside down or impossibly cranky would be next to useless I think, and if it did not float upright then you would not be able to cling to it for long.

    Unless you are prepared to convert some of your interior accommodation into major buoyancy chambers (such as sealing off the forepeak and afterpeak behind watertight bulkheads) I doubt if your little boat awash would be much use as a life raft.

    I have just come back from 8 days coastal cruising in a mini-cruiser (17’) and I have to admit, the thought of sinking at sea never crossed my mind. (I did nearly sink the boat on a rocky beach one night, but had the worst occurred, I would have walked away from that.) This little jaunt gave me an opportunity to think a bit about the best use of a very small interior.

    Here are some thoughts. My little boat was originally unsinkable due to the entire volume under the four quarter berths being one large buoyancy chamber. I am not sure how useful this would be to survive a swamping at sea – it would depend on where the boat was holed and which way up it would float. Anyway, that feature had been destroyed by the previous owner who cut hatches in the bunk bottoms with a view to using that volume as storage. I have found (single-handed cruising) that only one bunk is necessary, and that by throwing out the other three squabs I can carry all the food, clothing and equipment I need in plastic containers on top, so the entire volume under the bunks might as well be filled entirely with foam. That space is such an awkward shaped volume as to be of minimum use for storage and once gear ends up on top (which it inevitably does) I am too impatient to be bothered delving under the bunks. I am not going to bother filling the space with foam because I can’t envisage sinking off the coast (except maybe near to the shore) but perhaps I had better “touch wood” while saying that. Anyway, if I were looking for floatation volume, that's the interior volume I would sacrifice first - that gets you to stage 1 (unsinkable) but there is more to consider. My (shamefully vast) experience in capsizing dinghies  tells me that the really useful bouyancy is high up, under the deck, if you want the flooded boat to remain upright and have a chance of providing a survival haven, or bailing out. Its not just a matter of floatation volume, its where its placed that matters.

    The area low down under the cockpit in my boat is too valuable a space for water stowage and batteries – heavy things should go down there anyway, not foam. I am afraid I can go a fortnight without a bath while away, so no need for 200 litres of water. 50 litres is plenty for me for a fortnight.

    So, my thoughts are, if you don’t want water-tight fore and aft bulkheads, you might consider a horizontal bulkhead at the level of the bunk tops and sacrifice that beneath-bunk stowage space instead. Your proposed floatation test should not be for the purpose of seeing if the boat will float – you can calculate that – but it might be a good idea for the purpose of seeing which way up it floats and how stable it is in that attitude. My guess is that in practice, it still won’t be a practical liferaft.

    A quick fix is what you want, so you can spend your time sailing instead of a whole summer working on the interior of your boat. I wonder if it would be possible to dismantle the airbags out of a car from the wreckers yard. I have no idea if this is feasible, but they are very compact and (I hope) very reliable. If you could put a couple of these in the right places (so the boat  would float, and float upright) and devise a way of triggering them, you might have a quick way of retaining your boat interior as it is, and having it pop into liferaft mode in an emergency. Pre-test might be a problem! You would have to rely on faith that they will inflate – just as you do in your car, when you drive to and from your mooring. This might sound a bit crazy, but its an alternative paradigm and maybe it will spark a better suggestion from someone else.

    Last modified: 02 Dec 2019 05:05 | Anonymous member
  • 01 Dec 2019 22:41
    Message # 8148577

    Hello everyone. I have been too unwell to be very active on these forums or my blog for several years, but I seem to be recovering (at least temporary) and I'm hoping to carry out one of my bigger projects on Tammy Norie this winter. I'd be very grateful to benefit from for your knowlegeable thoughts before I make committing moves!

    To quote my project goals:

      Increase chance of survival in the case of a hull
      breach or other catastrophic failure at sea, especially on long
      distance solo passages.

      Reduce chance of loss of boat and all it contains.

      Provide other benefits such as insulation, soundproofing, and padding.

    And the main part of the design:

      Attach closed-cell foam to the hull so that over 1 tonne of
      seawater would be dispalced by the air in the foam even if the boat
      is fully submerged, creating an upthrust greater than the weight of
      the boat [RB-2015-06-09] [RT-2007].

    Now this isn't strictly about junk rigs!  But it is similar to the method that Roger Taylor has used on both Mingming and Mingming II for his voyages to the arctic so it is at least tangentially related to junks. What's more, I trust the experimental and lateral thinking of junk rig sailors more than most. I hope you'll forgive me asking here.

    The full plan (updating frequently) is over here on GitHub but you'll need to be fairly adventurous to go in there.

    There is an introductory blog post in the "Unsinkability" category on my blog and more will appear there as I go along.

    Finally, it's really good to be back!

    Last modified: 01 Dec 2019 23:00 | Anonymous member
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