I was thinking about fleets, and i have some ideas.
- There is no monthly upkeep for fleet (except for small amount of payment for crew)
- Quantity and quality of ships depends on amount of coastal demesne, special buildings and country modifiers.
- Price and time of build could be affected by modifiers like wood availability (wood in coastal province, wood in your domain, wood in your liege domain, imported wood), buildings and country modifiers.
- You can order fleet from your vassals, directly or from other countries like republic of Venice( Kievans did this when they invaded Byzantium).
- You pay for supplies once and you can replenish them in ports, port owners can allow this (they get some money and small amount of opinion boost) or refuse (medium- big opinion fall).
- Their choice has consequences, for example port owner is tributary of a country that is at war with you and he allows you to replenish supplies, that country can lower their opinion with port owner, increase tribute, start quick punishing war, ignore etc.
- You pay in ports for repairs, price also depends on buildings, province etc.
- After war and returning to home you can try to sell those ships to other countries, to local merchants or just cut them for wood and sell it.
- If you have certain tech advancements and decision you can turn your fleet into standing fleet, amount of ships depends on buildings in port.
- Each ship has age, older ship - weaker stats and bigger repair price, many age tiers.
- You can modernise your ships, price depends on their age tier, buildings and country modifiers, cost of oldest ship modernisation is bigger than building new ships.
- Ships with time get modifiers like good crew, famous, undefeated etc. for morale and combat. This is to justify modernisation and for larping.