[b]Ahoy there sea-enthusiasts,[/b]
This is not a rule but a more of a [b]courtesy[/b] for boat owners if you board up their vessel or just strolling down the pontoon,
1. Never wear black sole shoes. Owners will get frustrated if you dirty their deck with your shoe marks. Wear a white base shoe. Preferably with grip. And make sure it is a slip-on. You dun wanna end up swimming with your Adidas.
2. Wear a shade. Protect your eyes from the sun. Since you are at the sea, you'll tend to get double dose of the sun. Directly from the sun, and its reflection from the water.
3. Wear something cool and comfortable for you to move freely since the weather here is hot. Long sleeves and short bermudas are common among sailors.
4. Wear a hat. You wouldn't want to end up looking like a prawn.
Well said Nautinst!