Long ask sorry! I know you’re kinda covering the special cases of naval warfare with Constantinople and Blackwater, but I was just wondering how these battles normally occurred. It’s obviously before pre-gunpowder so was it mostly based on ramming like with classical triremes? Was the intended effect more immobilization or sinking? Additionally, what was the composition of navies? I know the Chola and Song dynasties had large standing navies, but what about Europe? Was it more merchant marines?

You’re more or less on-point – at least in the Mediterranean, where galleys were dominant and combat was pretty similar to classical Greece and Rome, focused on either ramming or boarding or disabling your opponent’s sails and/or oars. 

However, in the North Sea, the Channel, the Baltic, and the Atlantic, sailing ships predominated over galleys because of the rougher waters – yes, the Viking longship had both oars and sails, but they didn’t really use galley tactics due to their smaller size and number of oarsmen. Hence, boarding was the whole game.

One thing that did distinguish medieval from classical naval warfare is that you essentially had the importation of the castle onto the sea. Hence, you get ships like these: 

The forecastle and aftcastle got their names for very straightforward reasons – they were basically big wooden castles on either end of the ship that let you shoot your enemy from above and made it more difficult for boarders to come to grips with you. That, plus the fact that in order to support these castles you had to build bigger and taller ships which could just ride down the very low-lying longships, made these ships dominant in combat (although less seaworthy). 

In terms of composition, it varied. To take the English as an example, there was both a royal navy, but also localities like the Cinque Ports and Portsmouth were also required to maintain ships, and mercenary fleets were hired, and merchant marines were impressed, at various times. Likewise, at  times the royal fleet consisted of only two ships (in the reign of Richard II) and at other times as many as 700 ships (in the reign of Edward III). The thing to keep in mind is that wooden ships don’t have a very long lifespan, so unless you’re consistently putting money into maintenance, repair, and replacement, you can build an entire navy only to have it vanish, requiring a new navy to be built – which is one of the reasons the numbers and composition varied so much.