There should be more of a naval arsenal at your disposal I think this would make the water alot funner , for example ES should make a Pirate sort of ship. Sort of like a fireship it get adjacent to you then boards your ship by dropping tall wooden post with hook like thing on the top of it that is dropped into the opponents hull. Then melee units that are garrisoned in the boat run across the board that is now in the enemies ship theres a little fight of the enemy boat crew and your pirates then it is your boat to control. this boat could be another counter to a siege ship or arrow ship.
A counter to this pirate ship could be a mix of a fireship and demo ship of AOK its very fast small ship that when adjacent to an enemy ship it lights it on fire and the enemy ship slowly loses HP and sinks.
A counter to this could be a large ocean going monster of a ship that when these pirate or fire ships got adjacent to it, it tosses down a large chain and ball on the ship and sinks it in one blow but these ships are expensive.
And to take out these ships you would probably use hit and run tactics, since its so slow. I think they should have big life size ships. And about the problem of ships not being able to go in canals. Most ships didn't go into small canals except longboats . but you could fix this with making small versions of the same boat. For example a heavy ram and light ram, Heavy and light transport and so on... I like the idea of a heavy transport, it lets you decide on how many people you need to move, and how much you can afford, and where it needs to go like in a canal or not. I also think there should be some sort of hero ship or something to counter myth naval units.
I think these improvements would greatly expand the fun of the water. I know this wouldn't make it into the game but they should put it in an expansion pack. So post your reply's comments flames whatever.
Strategist, Age fan, owner of AoM beta, and future game devolper.