If it isn't symbolic, I'd guess the swimmer had just decided to abandon all but the most important piece of his kit. The helmet would also afford him a bit of s

If it isn't symbolic, I'd guess the swimmer had just decided to abandon all but the most important piece of his kit. The helmet would also afford him a bit of safety if he stuck his head above water to see what's going on and where he is. Could also be a cuir-bouilli helmet/hat which I assume wouldn't restrict his swimming to the extent of bronze or iron.