I've done a bit of research for the navies for my ancient mod. The tech goes up to medieval although the idea is that people should not get there unless they really go heavily into naval research.
I try to use the advances that really allowed the new units, so you are really researching through the development of ships, not just general ancient technologies.
A key part of my ships is that I make all water cost 2 movement points. Then ships ignore movement cost for some of those. Shallow draft ships move fast in coast, larger ships move faster in sea and/or ocean.
Hull building allows canoe and war canoe. These are slow, light units. The war canoe provides token naval military power - enough to capture enemy canoes but nothing else.
- canoe 0/0/2, transport 1 foot unit, fast in coast, sinks sea/ocean
- war canoe 1/1/2 -2 hp, fast in coast, sinks sea/ocean
Amphibious Warfare requires warrior code as well. It does not provide ships, just marines which are an axeman with amphibious.
Outrigger allows outrigger canoe. It is just like a regular canoe (0/0/2 transport 1 foot unit) but it does not sink in sea. It still moves slowly in the sea. This is a quick unit to get for sea transport and it does not require timber - all ships beyond this require the timber resource.
Carvel hull is making hulls from planks fitted next to each other. It allows for larger ships to be built. The two ships are the roundship, 0/0/3 can transport 2 units, and the penteconter, 2/2/3 -1 hit point (all galleys have -1 hit point). Both ships are fast in coast and sink in sea and ocean.
Piracy requires Warrior Code as well and allows the building of pirate galleys - essentially penteconters but they have hidden nationality. They are used for commerce raiding, not warfare. Barbarian ships are pirate galleys.
Clinker hull is a sturdier ship design with the planks overlapping. This allows the drakkar, and knarr. The drakkar is a raiding ship, a 1/2/3 that can transport 1 foot unit - it does not sink in the sea but is slow in it, it is fast in coast and sinks in ocean. The knarr is a 0/0/3 that can transport 1 unit. It is fast in sea but slow in coast as it has a deeper draft. It sinks in ocean but not sea.
Banked oars require carvel hull and outrigger - the oars are attached to the outrigger for extra leverage. This allows for larger galleys: the trireme and the bireme. The trireme is a 3/3/3 -1 hit point warship that can transport 1 foot unit. The bireme is a smaller ship with the same offensive ram but less capable of defense 3/2/3 -1 hit point with no transport capacity. Both are fast in coast and sink in sea and ocean.
Slave Rowers requires slavery as well as banked oars. It allows the construction of a slave galley - essentially a trireme but it can enslave its victims and turn them into slave galleys as well.
Naval engineering requires engineering as well as banked oars. It allows for extra large galleys, large enough to carry catapults. This allows the quinquireme which is massive and slow, a 3/3/2 -1 hit point. It includes an intrinsic catapult for both land and sea bombardment and can transport two foot units. It is fast in coast and sinks in sea and ocean.
Lateen sail is a triangular rather then square sail. It allows for liburnia, fast and light sailing galleys 3/1/4 -1 hit point. They rely upon speed to attack much larger ships. It is fast in coast and sinks in sea and ocean.
Square stern is a development to widen sailing ships. It allows for the cog, a larger version of the knarr. 1/1/3 it can transport 2 units, it is slow in coast but fast in sea and does not sink in sea.
Trimming is a late refinement to galleys, making them sleeker and faster with fewer rowers (then the quinquireme). Their new design is simply superior, including even a catapult. This allows for the dromon 3/3/3 -1 hit point. It includes an intrinsic catapult for both land and sea bombardment and can transport one foot unit. It is fast in coast and sinks in sea and ocean.
Skeleton First construction is a radical ship design where the hull is built last, instead of first. This allows for the building of much larger ships, stury enough to be ocean going. It comes much later then the ancient age and is included only to allow for ocean transport if required by the map. It allows the caravel and the carrack. The carrack is a huge ship 2/2/4 capable of transporting 4 units. It is fast in sea and ocean but its deep draft makes it slow in coast. A caravel is a smaller ship with a shallow draft allowing it to operate more easily in coastal waters but slower in ocean (although it does not sink in sea or ocean). 1/1/4 capable of transporting 3 units. Note that neither ship has cannon or even catapults - they are merchant ships with only the defense afforded by their high sides, sturdy construction, and crews.
