Crew Combat:
Currently, the crew don’t do anything, so this should make them more useful.
Warding off pre-mature boarding:
As of right now naval combat is often skipped when facing players, or infinite stamina ever pursuing marines hellbent onboarding your ship instead of engaging in traditional combat.
This could be solved by placing crew armed with muskets or spells on the deck and in the rigging, that automatically fires at anyone too close to your ship. However, they can be killed either the traditional way or by depleting the Ship’s HP.
Boarding:
When at a reasonable distance from a sunken ship, the crew will holster their muskets and spells and pull out their swords and melee weapons in preparation for the board. Also stopping their captain from just sitting back and letting the crew just pick out the survivors.
Lowering your sails next to a sunken ship and letting go of the wheel will make your crew board the ship, except for the men on the rigging who will still shoot.
Loading Cargo and Loot:
Crew can also be ordered to load and offload cargo and loot, from shipwrights and sunken ships. However, in doing so, they also take a share of the profits with them.
Mostly as an anti-frustration feature, as manually buying, loading and selling cargo and loot can be rather exhausting and tedious.
Crew Status and gear:
Considering that crew can be killed, they could either be regenerated in several ways,
Waiting for the crew to respawn when out of combat -
The slowest way yet the surest way, waiting for enough time make a replacement pop out from under the deck.
Impressing surrendered enemy crew into your service -
When boarding, the enemy crew may surrender, if their captain dies, or their crew reaches a low amount. Interacting with them will allow you to join your crew as a replacement, or you could just kill them.
Hiring replacements in friendly ports -
Visiting a tavern (or their like in the town) may have shipmates, willing to join for a small fee.