This is doable with 2 devices (like 2 Xbox or PC by installing the game, or using xCloud) and a dummy account on your home console).
Start to sail with your main account and invite your other account, you will be in a crew.
When characters are facing each other, equip swords by pressing
.
With your first account, press and keep
, with the second account press
to attack, then press
with the first account.
There will be no damage but the achievement will unlock.