I don't know anything about coding, but some small modifications to travel routes might suffice?
As a noble (with a non-cavalry unit smaller than XX people -- 40 perhaps?) when in a city, you could choose to "Hire a ship and crew" for XX gold (depending on the distance). The captain promises you he'll drop you off in that coastal region within X hours. (However, seeing you're at sea you won't be able to receive messages for the duration of the trip, nor will you be able to get off anywhere else or return halfway = optional)
Events:
*The wind and current worked along great, you have arrived X hours sooner than expected (= a lot faster than land-travel)
*The weather could have been better, but the captain kept his promise: you made it to X on time. (= still a faster than travel by land)
*The ship got lost in the current, and you have arrived after a delay of X hours (= similar travel time as land-travel)
*Pirates! Your captain skillfully managed to avoid them, hiding in a small cove. Just to be safe though, you agreed to take refuge there for the rest of the day (=arrival X turns later than land travel)
*Suddenly a storm broke out (? idk the proper expression). The sails ripped apart and one mast badly damaged, the ship is adrift for several days. When the sky finally clears up, your men help the crew rowing ashore (=resulting in a morale loss + equipment damage). Checking your surroundings, you conclude you have stranded in region X
Every event would have a certain chance of occuring, also depending on the weather. In winter, for instance, storms might be more frequent (so it's a bad idea to take to the sea) and in summer, the chance of pirates would increase.
Overall, though, transport at sea would be faster than over land, assuming you're prepared to take the risk. Massive amphibious invasions would be out of the question, as the army would get split up along the way. Furthermore, seaborne expeditions can only depart from a city (with a harbour?) and end in allied or neutral lands.
Thoughts?
