How do I make a good solo quest?

This one goes out to all the DM’s in the castle.
I realize that a solo quest is generally easy to make, just lower the amount of enemies so you don’t kill the main character.
HOWEVER!
What if I was doing a pirates/space pirates/smugglers (could go any direction) game, as a solo quest, and eventually might run into the possibility that my player’s character wants her own ship, or perhaps pulls into port and gets a job on a different ship, or something like that with tons of NPC’s in the rigging, bilge, cargo bay, engine room, or whatever. Ships need lots of people, and until you reach your destination, that’s all you’ve got, is your shipmates.
How do I make a solo quest out of this?