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Thread: Use of SAP in Ship Safety

  1. #1

    Lightbulb Use of SAP in Ship Safety

    I don't know if anyone has ever thought of the uses of SAP outside nappies? I doubt anyone has ever thought of it to stop ships capsizing though

    SAP (super-absorbent polymer) can apparently hold about 30 times it's own weight in liquid. It has been used in nappies and other absorbent consumer goods, and some industrial applications like mopping up spills of liquids such as in pubs and cafes. It essentially locks water into a gel and makes it easier to mop up without spreading the water. I've used the insides of a Tena Slip Plus to quickly clean up a spill of water before it could do any damage to my laptop.

    I am wondering if it could ever be used for anti-capsize in ships and other watercraft. My theory is that if the water is contained in a gel it can't slosh around. This means that it won't change the vessel's centre of gravity during rolling movements. This in turn would prevent capsize when taking on water, either through an open door or through a crack in the hull. It may have prevented the Herald of Free Enterprise disaster at Zeebrugge in the late 1980s, as it was found in the investigation that the rolling movement of the ship, the free surface effect (slosh dynamics) and the huge amount of water in the car deck is what caused it to capsize. If the water was contained in a solid, it wouldn't have rolled over as it would still have been stable or so my hunch goes.

    I have no idea how much a few tonnes of SAP would cost or how effective it would be in sea trials at stopping capsize when taking on water. It may slow the rate of water intake as well by expanding to fill the crack in the case of a cracked hull. It may slow the ingress of water and it's slosh dynamics enough so that the master can take control of the situation and declare mayday and launch lifeboats or just return to the terminal if he's not quite left the harbour (as in the HoFE disaster).

  2. #2


    I am not a scientist or anything, but all that contained water would still weigh the same (and then some).
    Waves could still affect that. Ever poked a jello and watched it jiggle?

    And non contained SAP is not really a solid, I have burst enough diapers to know that
    Clean up is a mess.

  3. #3


    Yeah I see what you mean, it would need to be contained as it'd just roll around all over the place. Still if it could reduce the slosh it might buy the master some more time before the vessel turns on it's side. I suppose I'd need to invest in a supercomputer and some computational fluid dynamics software to find out any more than that though lol. Either that or build a scale model of a ship, stick a Tena in the hull and plonk it in the bath and see what happens.

  4. #4


    baffling is the best option, but that would occupy space or make space less accessible, and when you're in the business of filling space, time and space equal money.
    and don't forget that the water would need to be pumped out, in whatever form it was in.

  5. #5


    And, let's face it, dewatering a space filled with a liquid is faster and easier than removing any variation on a solid.
    Given the relative lack of OTHER things wrong with the crew and status of the HoFE, I don't think that any additional measures would have been implemented. The biggest issue there was discipline and poor procedures for ensuring Seaworthiness: I'd have to look into more, but I suspect multiple violations of the OpMan and STCW.

  6. #6


    The gel produced by the combination of water with SAP would be extremely difficult to pump out of the vessel. This increased mass is what reduces the vessels buoyancy, lowering it's water line, and making it easier to wash over with water and capsize.

    I congratulate you on your cunning plan to kill countless sailors.

  7. #7


    SAP is also used in tunnel waterproofing. I saw a presentation from a vendor for use in subway construction. The primary waterproofing is a thick vinyl film that's wrapped around the tunnel or station box. If it somehow gets punctured during construction or operation, there's a layer of SAP to soak up the leak. There's no way to change the SAP, though, so I wasn't sure how well it worked once the SAP was saturated. I imagine the warranty period for the product is just long enough that the manufacturer doesn't have to deal with it.

  8. #8


    Ah well it is a duff idea after all Well I suppose that's how we learn - ask questions and see what people who are more learned say . I expect that to remove the sap it could be sucked out with a giant hoover or with a JCB. Wouldnae be easy in the bottom of a ship though - or in a tunnel for that matter come to think of it. I suppose that SAP is best left in nappies really lol.

  9. #9


    Different field entirely, but a very "you mean they didn't think of that before?" application I just saw is in the tips of microneedles (not very 'micro' in the demo at least) to "tack" skin grafts in place. Apparently the stuff available now (staples? ouch?) isn't very advanced and has a number of problems, so creating an artificial "barb" that can go in sharp and expand enough to hold is a major advance, and offers the opportunity to dope them with antibiotics or growth factors or pain-relievers.

    No link handy but the demo was basically a grid of plastic 'studs'/tacks/rivets through a sheet of tissue or synthetic tissue. So, um.. -ouch-, but apparently this'll be a major advance over just trying to go around the edges or causing less 'secure' locking where fluid can build up/things move around too much and the graft doesn't take.

    - - - Updated - - -

    Hey, before ditching (pun happens) the whole idea, might it have some advantage in a waterproof cement mix, or already be in them? I'd figure the tunnel lining might be something like that - enough to reduce the mechanical stress for another compound that'd otherwise wash away to harden around a slow drip before it becomes a torrent.

    Not sure how that works for a ship where the mass of the 'leakstopper' has to be weighed against just making the hull sturdier to begin with.

    Sounds like the "buying time" might make sense if a system's in place to take on water ballast in a controlled way and/or to displace the stuff out of the hull, so maybe the question is what becomes viscous on contact to damp the "slosh" dynamics but still easily pumpable.

    Or, of course, put it outside the hull, or between double hulls, so it's really acting to seal off the leak rather than just manage the dynamics. If the stuff is roughly the density of water, is having a glob of it outside the ship and under the waves going to be as bad as losing displacement?

    - - - Updated - - -

    ... wonder what the dynamics / compatibility is with a really fast water-activated adhesive like cyanoacrylate (crazy glue), and/or if the exothermic aspect of that would in turn be enough to set silica in any useful way...

    Meanwhile this pops up just searching for 'self-sealing marine bulkhead' so some people have probably put thought into it!

  10. #10


    As far as stability goes, many boats can maintain positive buoyancy with large percentages of their below waterline volume flooded, provided the surface effect of all that water is minimized. After that, the real trick is rapidly dewatering the space, and patching/plugging the hole.

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