What do you think of correlating the movement speed of ships in battle with their movement speed on map? Currently making a fast ship doesnt benefit you as much in battle especially with long range ships/ that keep out of the fight anyway or ships that dont have a big bridge, if movement speed was a factor on the strategic map there would be more depth in ship design dependent if you want it to be a big siege vessel or a quick response ship. On a similar note maybe add range depending on coal supplies so you have to refuel from time to time.
Speed is a big factor when you make ramming ships. That's it mostly.
I outlined an idea for a turn/tile-based command mode in another topic, and suggested that the range of each ship per turn should be determined by it's speed.
Of course, your idea could be implemented into the current command mode just as well. Making fast ships would be well worth it, because you could send fleets to defend your cities that will be imminently attacked, and make it in time.
The only downside is that fleets would have to be divided into slow ships and fast ships. (because I assume a fleet would go only as fast as it's slowest ship.)
Captain, Engineering Corps
Well, having fast ships can be very useful in battle because you can get to where you want faster and have a better response time. And like @Slimy said it also is very useful for ramming.