Battlle of Lepanto is the sea battle between the Christians and Moslems in the Adriatic Sea that aims to be much closer to the real battle than the offering that came with the expansion.
You should play on hardest difficulty.
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.