This is a single player scenario which aims to be much closer to the real battle than the offering that came with the expansion.
In the scenario, your only economy is what you trade and it is your trade routes you are trying to protect.
Uniquely, you can buy special boats for 200g by visiting a neutral port. These boats are boarding ships. They are "Monk converting ships" that are special units created by the designer of the MAP TRICKS! Scenario which convert enemy ships like monks. Please download his scenario for other interesting novel units.
You are defensive in this scenario. You may think nothing much is happening for the first 45 minutes, but I am afraid a rather unpleasant shock may be in store...think big!