First, get a female crew (cosmetic ship skin). There are multiple of these in the game, but the following are the easiest options:

Get "The Assassins (Female)" from Ubisoft Club for free, as it just requires a Uplay account. In the map menu, press Left and select the "Ubisoft Club" option.
Find "Bandits (Female)" at the "Sunken Wreck Of Datis" underwater location, southwest of Delos Island.
Complete the "Olympian" questline ("Going For Gold" trophy).
Complete the "Daughters Of Artemis" questline ("Master Of The Hunt" trophy).

In the ship menu, select the Female Crew cosmetic item in the bottom right corner. Leave the lieutenants blank (no female lieutenants required for this). Then, disable a ship at sea. Shoot it until it is disabled, but do not board it. Ram it at full speed at its center (hold X to speed up) to break the ship in half and get the "Ramming Speed" and "Wrath Of The Amazons" trophies for cleaving a ship in half and for cleaving it with a female crew.