I'm not sure about a large crew's survival, I played most of my time solo. Here's how I survived:
Keep your eye's PEELED! I was always looking around for ships, and if I spotted one, I never looked away for extended periods of time. I always tried to keep a mental note of the direction the ship was to me, and what direction it was traveling.... (That's easier said than done though, it takes practice.)
If I was focused on loot, I always avoided direct confrontation.... Someone posted the phrase, "If you're playing solo remember, you're not a pirate, you're a smuggler!" (I'm sorry whoever you are, I can't remember your tag.) I took that to heart and as a result, I never got abused by PvP happy players.
Never collect more than 2 or 3 chests at a time, even if your voyage is a long one... When you're solo and you need to turn in more chests than that, your chances of being pirated go WAY up. It's not easy to avoid getting your ship sank or treasure stolen if you have to run away from your ship over and over. (Never keep a Chest of Sorrow longer than you have to. If you find one, abandon the rest of your search and turn it in right away.) It's really hard to avoid people or PvP if you have to, while that b******d is filling your boat with his salty tears.
When you're on islands looking for treasure, keep a mental note of where you docked, and ALWAYS be looking out to see in different directions for other ships. If you spot one, stop and see what they're doing and try to determine if they've spotted you... It's never a bad idea to abandon the island and come back later. If you don't dig up the chest, they can't take it, and that island isn't going to float away on you.
Never pull into an outpost on the opposite side of the chest turn in... And also, learn how to pull into outposts and islands really close, without damaging your ship. Once there, turn your ship to the open sea. Then: Straighten your steering wheel 1st, Raise your sails 2nd, and Raise your anchor 3rd, and last, pre-position your sails to have the best wind possible for when you drop them.... These things will make it SUPER easy for you to get away from opposing ships, even if they get the drop on you.
If you're cornered or being chased, remember to use the map to your advantage. Sail around rocks, against the wind, into storms... If you're playing solo, you're going to learn your way around sailing that sloop real quick, and it can make it very hard for anyone except another experienced sloop captain to catch you.
Use NPC's to your advantage. If someone is just relentless in chasing you, and you can't out maneuver them... Sail close to forts and islands that you know have cannons on them. Zig Zag, and let the skellies take it from there. Those bone heads are insane shots sometimes, and they will most likely take care of someone that's chasing you... Not to mention, if you get good at this, you can avoid most player shot cannon balls at ANY given time. You're never going to avoid them all, but all you have to do is avoid that one extra one that sinks the other ship lol.
The MOST IMPORTANT piece of advice I can give, in my opinion, is be patient. The only real variables in the game are other players, the outposts and NPC's aren't going anywhere, so it's not always a bad idea to sail around and wait for someone to leave an island you have a voyage on, or leave and outpost you want to stop at... Although you can just sail to another outpost.
This is all I can think of off the top of my head. There's TONS more, and I'll come back and edit as I remember stuffs. :)
If your voyage brings you to an island thats on the edge of the map, always sail around to the back of the island closest to the edge of the map. This eliminates almost half of the directions an enemy ship can come from, and most importantly, spot you from.
EDIT: @KattTruewalker Turn off your lights!!!! I got so used to doing this that I didn't even remember to tell people lol, nice shout out!
