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).