Rosie, as you probably know already I used to work for Vickers Armstrong shipbuilders at Barrow so was privvy to witnessing quite a few dynamic launches ,admittedly in my time they were Royal Navy vessels, however the principle is the same, regarding the drag chains,---- Huge cast hooks (for want of a better word) were litterally bolted to the sides of the ship, and the drag chain fixed, I don't know how those clever people managed it , but each drag chain took its own weight by a method of hawsers so that the side of said ship wasn't ripped out. Also some very clever people estimated the weight of chain necessary to bring the ship to a standstill within a certain time, e/g QE2 had the tightest of space to stop moving. All this done with slide rules , experience ,& when you watch the rest of the series of The Liners, a few tight buttocks, likewise at Barrow, Walney channel is really tight for space, so after a launch the need to bring a moving mass of soooo many tons is paramount. As a total side line here, a lot of years ago we lost a submarine at launch, there is always a finite point with tidal launches, to launch just before the tide stops running (gives a reasonable amount time in case things go wrong ) anyway after she was in the water, all the lines thron from her to the tugs just missed, meanwhile with the tide still coming in at a rate of knots she drifted very quickly out of the dreged area & ended up on a sandbank, quite safe, but very embarrasing when the tide went out she was over at quite an angle untill 12 hrs later under cover of darkness the refloat & recapture were carried out. After that a clever but simple device was fitted to the upper deck, consisting of a pointy bit of steel, this captured a hawser during the launch, said hawser was attached to a tug, simples as they say on the telly, I'm afraid that launces down a slipway are a thing of the past, I'm really priveleged to've been there & seen it. Will try & search out some photos of big hooks on side of ship to post...