This may not be of much interest, but I thought I put my thoughts here in case anyone wanted to research it...

Sea, as I'm sure you know, can be placed on the campaign map land area (as if a wide part of the river, a river lake or stand-alone lake).

Ships can sit on sea.

Ships can load and unload troops.

Ship models can be modded.

Do you see where I'm going?

A faction-controlled ferry!

I'm talking landing platforms on either side of the "river", and a rope-guided raft/boat owned and controlled by one faction.

I'm not sure if boats/admirals can be bribed...but that would mean the ownership could change.

Ferries would thus have huge strategic value.

Anyway, those with more time and skill may wish to continue this.

I await all the reasons why it is not possible ;)