Ranking the Best Sea Units

This is an overview of all sea units you can get in Grepolis. I compare and rank their power in attack and defense. The attack and defense power is shown in points as per population (i.e. if a light ship uses 10 population, its attack power has been divided by 10). Sea units are highly specialized; always take a second look before rushing into something. Please note that this post includes the new unit Siren from Beta.

The Grepolis wiki shows attack and defense power per unit. For my ranking, I have calculated the numbers as per population used for any unit (i.e. if one Hydra uses 50 population, the attack and defense power is now shown as divided by 50). The ranking lists below show the attack and defense worth of all available sea units.

Ranking the best sea units for effectiveness in attack:
26 Hydra#
20 Light ship
16 Trireme
11 Siren#
03 Bireme
00 Fire ship
00 Transport
00 Fast transport
00 Colony ship

While this list shows attacking power, it says nothing about defensive values, speed or cost in resources and divine favor. There are a few other things you should know when attacking. While Hydra and Siren can't be sunk by a fire ship, one fire ship will sink one attacking light ship, one trireme, or one bireme one on one. The battle points are always in favor of the fire ship in this exchange as it uses less population when being built than the attacking units.

Fire ships can't attack, Grepolis won't let you. They can only be stationed in a harbor to defend. On the other hand, transport, fast transport, and colony ship can attack, but they have no weapons on board to hurt a sea unit. If they attack alone, a single Hydra, Siren, light ship, trireme, or bireme in the enemy harbor will sink the lot including whoever is on board (talk of the Titanic). They always have to be escorted by one of the three top ranked attacking sea units. And don't waste your biremes on attacks.

In one world I played ages ago, I had one specialist who always sent his attacks with transport only; sometimes I earned 5,000 battle points or more with a single bireme sitting in the harbor until someone came and killed it.

Ranking the best sea units for effectiveness in defense:
28 Hydra#
20 Bireme
16 Trireme
11 Siren#
06 Light ship
00 Fire ship
00 Transport
00 Fast transport
00 Colony ship

Fire ships only work as the last defense, meaning that all other units in the harbor must be dead before the fire ship jumps into action. Fire ships can't touch the ships with an attack value of 0. This means that while a single bireme can sink a whole fleet of transport ships and a colony ship with the entire army when attacking unaccompanied by light ships, the same army will be all over your city if there are only fire ships to defend.