Do I need a navy?
I’ve heard several times players claiming that you don’t really need war ships in Ikariam anymore once you get the occupation technology. Then you can occupy other players cities and use these as a base to launch attacks after all. I agree that it’s really usefull to be able to avoid other players fleets now and then, but you can’t depend on this strategy for 100% of your plundering.
For one, on some islands everyone has a tiny navy in their cities and then you are not able to occupy a city there without using war ships. More frequently however, there will be 3-4 small cities on the island you can occupy. Using a small city as a base to attack from is not optimal though, they often have tiny trade ports and few action points. If you have to use a long time to load resources and troops you will give the enemy more time to block your city with his fleet, and then the resources will be lost.
Even if you manage to occupy great cities to plunder from frequently not having a fleet of your own still makes you very vulnerable to harbor blockades in general. It’s really easy for your enemy then to just put a few war ships in front of each of your cities, and stop you from both moving troops and resources around. With no fleet of your own it might take you a long time to get help from allies to lift these blockades, and you may end up loosing lots of both troops and resources over this time. My general advice is to have at least 3 war ships for every city that you have for the first few months of the game, and just keep increasing it as your neighbours do so.