A related oddity - according to "Navies of the Napoleonic Era", Turkish ships had higher decks than was normal for other navies allegedly to allow for elaborate headgear, even though this actually compromised the stability of the ships.
If you're shooting, or dumping burning oil on your enemy, or even throwing rocks at them, being a bit higher than they are is a significant advantage, if for no other reason than the fact that you can see them better than they can see you. It's like the high ground in land battles.
This is in Napoleonic times, where naval warfare relied on broadsides of cannons. Stability is a far more important factor here. Also note that 4-decker ships, with a nominal advantage in firepower, were employed by the Spanish but eschewed by the Royal Navy for the same reason.
Is that a hold-over from Byzantium/Eastern-Roman-Empire, kept after the Turkish conquest? They were all about elaborate hierarchies of ranks and titles, often expressed through big hats or helmets.
Neat idea, but I'd bet it was a completely native decision, maybe forced on some poor naval architect by a grandee who didn't understand the implications of the order. Then again, there's no proof one way or another.
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.
Yeah, in general that wouldn't be surprising. The OP describes this guy as a "soldier", but I wonder if there's enough info to know whether he's just a soldier perhaps someone more important.
