I like this thread. I am very curious about the details of combat. I have not had much sword fighting experience BUT IT SEEMS LIKE you can block and after three hits there is an opening to get a hit or two then you should block again unless you are lucky enough to get a stun lock going on. I learned that swords are way better than guns up close obviously as it should be haha. You stun lock and thats it, only possible chance is the blunderbuss to the face. So I typically run in shoot my blunderbuss and go sword right away.
Ship combat I learned the same about the barrels haha I typically keep them up in the crows nest. You can keep them safe ish below deck but boarders will destroy you in a second so crows nest is my suggestion. Also, ships are pretty much unsinkable without some form of boarding team or at least killing them off on the deck with cannon fire. Seems the best strategy is to go into a slow half or less sail length instead of anchoring because then youre a sitting duck. At half or qtr sail you can easily pick up speed again if overwhelmed or just drift by landing lots of shots. Just know boarders are a bigger possibility at slow speed although not as bad as anchoring again as to why I avoid that.
Taking on more than one guy is pretty suicidal (i always play solo) Yes sure you can get lucky but if there are straight up two guys and you on a beach you better run and hide at least to make them come around corners so you have your blunderbuss ready or something. Don't be on an open beach. Climb up ladders and mountainsides. Use the enviroment.
Leave a cheap chest somewhat in the open and hide your better stuff. A lot of people find that and think thats it. So maybe not full on pvp but it is psychological pvp haha.
All of this came from my pvp experiences.