Why ?

Why on earth would anyone spend good money on a brand new chain, go to the trouble of anchoring it in the ground and then padlock it to a set of pontoons which must weigh a few tonnes and be at 20 x 15 metres ?  

The 2nd photo (first time I have ever added one) shows the pontoons in question. So if you were of a mind to steal one, you would need to turn up with at least a large crane and a low loader. In which case, I doubt if the chain would be much of a deterrent.