Great thread
Water was the avenue for trade, which was the foundation of national wealth in the period of industrialisation - so navies should be incredibly important as the protectors of this trade at the very least, although there's also gunboat diplomacy (threatening coastal cities with firepower from a relatively powerful naval vessel could win trade or other concessions) and the support of amphibious landings (landing an army on hostile territory).
The period in question (1830 to 1930) is without question the period of the most radical technological advancement of naval technology as well - which matters because of their strategic economic importance. I very much hope that dreadnoughts won't just be a technology buff to "battleships", as per Vicky 2, which made me die a little inside. I'd strongly argue that each stage of both "line of battle" and "cruising" ship should be represented by a different unit that has to be built.
Roughly speaking, and off the top of my head (at some point I'll put together something with a bit more research and thought behind it - the below would need refining and will have some errors - and is a huge oversimplification, but there'll be no war around that in-game) these would be (first is line of battle, second is cruising ship, third is coastal defence ship, fourth is torpedo warship/screen ship) - noting that time periods would overlap (names are very rough):
Up to about 1845 - Sailing ship of the line - sailing frigate - early paddle warship
1845-ish to 1860-ish - Steam-powered ship of the line - wooden screw corvette - paddle frigate
1860-ish to 1870-ish - Broadside ironclad - wooden screw corvette - monitor
1870-ish to 1880-ish - Central battery ship - unprotected cruiser - early coastal battleship
1880-ish to 1890-ish - Armoured turret ship - protected cruiser/armoured cruiser (two ship types if possible) - early coastal battleship - torpedo boat
1890-ish to 1905-ish - Pre-dreadnought - protected cruiser/armoured cruiser - less early coastal battleship - torpedo boat destroyer
1905-ish to 1915-ish - Dreadnought - light cruiser/armoured cruiser - basic coastal battleship - destroyer - early submarine - seaplane carrier (towards the end of the period)
1915-ish to 1925-ish - Super-dreadnought - improved light cruiser/heavy cruiser - improved coastal battleship - destroyer - submarine - early aircraft carrier (towards the middle of the period)
1925-ish to 1935-ish - Modern battleship - modern light cruiser/heavy cruiser - modern coastal battleship, modern destroyer, modern sub, improved aircraft carrier
There's also the introduction of naval mines, which from about the turn of the century were a strategically important naval weapon. How these are best handled depends on the level of detail in the system, from a modifier to naval blockades and a "random damage generator" to something more player-controlled and targeted?
As for the battle system, a "dynamic battle box" based off what's used in HoI4 could work well. The challenge is to only have the screen boxes show up when at least one country has developed torpedo boats (prior to the advent of the torpedo, naval battles were slugfest between the larger ships supported but not 'screened' by smaller ships, as there was nothing to screen them from), and then the carrier box to only show up once at least one side has seaplane carriers, and likewise the submarine box. The other challenge is that during the Victorian period there was a far greater number of warships with limited seakeeping ability - France at one point had a fleet that was primarily designed around coastal defence, with scores of torpedo boats that would have been useless in a seaway. To mirror this kind of issue (which was very much a strategic defence one) it would be handy to have some way of distinguishing between high-seas combat, versus combat in coastal areas where seakeeping and endurance are far less important.
As well as this, what's important is the industry that built the ships - heavy industry was vital for the construction of armoured warships (and industry more broadly quite important for the construction of wooden warships) - countries without that heavy industry needed to order their ships from abroad - the European countries and later the US building most of the ships used by smaller countries.
but that is primarily because there isn't much you can customise with Victorian and later game ships.
There were huge amounts of possible design options with pre-dreadnoughts and earlier - from the four-turreted ironclad (that was a converted ship-of-the-line) Royal Oak, to broadside ironclads, to central battery ships. There were huge improvements in weaponry, armament, hull design and armour (amongst other things) that lead to all sorts of designs. There is absolutely scope for an interesting gameplay loop from an MtG-style designer.
However, I'm not sure a MtG-style ship designer is necessarily appropriate at Vicky's level of abstraction, and the huge development in naval technology over the period would make it a much greater game design challenge as well. But something deeper than Vicky 2's representation of ships (that was arguably the weakest element of the game) would be most welcome. And if the devs wanted to make a game just for me, then for sure include a ship designer - but more realistically it's best to think of everyone else
fuel obviously wouldn't be an issue at the start of the game
The first operational deployment of a steamship by any navy was in 1824, Lightning, by the RN - while the vast majority of the game's warships were wind-powered in 1830, the first steam-powered warships had been built. The big thing here is the difference between coal and fuel, and should both be required for trade fleets as well? (I'd argue yes - making coal a very important strategic resource, as it was historically).
When a British reporter who observed the battle of the Monitor and Merrimack during the American civil war wrote back for his article to London he wrote that either one of those ships could single handedly defeat the British navy. Maybe a slight exaggeration, but the wooden hulled ships were no match for even the most primitive steel armored ships and I hope they properly reflect how quickly wooden hulled ships went from top of the line to totally obsolete in a short 10-15 year period.
Strictly speaking, ships without armour - many ironclads continued to have wooden hulls for quite some time, and many cruising ships continued to be all-wood (with no armour) or unarmoured (iron hulls, but just shell plating, no thick armour plates) for much longer than the "battle line" vessels.
The British reporter's statement is hyperbole as well - by the time of the battle between Monitor and Merrimack, both Warrior and Defence were commissioned, and far more importantly, the Monitor's abysmal seakeeping meant it was never a threat to any vessel outside of coastal defence role.
It is very much true, that, that armoured ships changed the battle line forever, and in a very rapid fashion. However, the change to steam-powered wooden-hulled battleships was also hugely significant - the tactical freedom provided by not being dependent on the wind being very important.
