Fireships and Trirremes

Some comments about each one of these naval units:

Fireships

• Second slowest naval unit, only behind the CS.
• Chepest naval defensive unit.
• For each fire ship, one LS can be sink.
• They don't kill Hydras neither CSs.

They can defend well against LS nukes, but birremes can do the same with a higher cost(if the number of birs are proportional to the number of LS, don't forget their attack x defense is 1 per 1, if you count pop per space). 

When your teammate need help, fire ships will take centuries to arrive and the city will probably be under siege or conquested.

Conclusion: Don't build them. They seem to be good in the beginning, but they are trash in the late game. When enemies are enemies are further away from you.

Trirremes

• So fast as FTS.
• Most expensive naval unit.
• Perfect to escort CS in Conquest Worlds.
• Good for defend and attack.

A naval unit that should be used in specific situations because of their price. You can surprise your enemies with an attack with trirremes in revolt worlds, but you can't use it in all your naval cities.

Don't forget to assign Eurybia to your trirreme city.