I'm honestly not surprised this is happening, what with the PvP land glitchers and spinning/infinite damage broadside hackers going around. As some stated above, sail with high level friends who, preferably, are good at PvP and have good weapons. This may sound stupid, but I would advise not to use Copperhead ships to plunder in busy servers until this is fixed. They are slower, so making it to port before everyone dies will be tougher. Like I said, it may sound stupid, but I'm one of the most avid sailors in the game, so I'd know. (Not saying I'm a better sailor than everyone; -I haven't SvS sailed in 3 months- I just -loot sailing- sail a whole ton more than 95%)
Have someone who heals ready if you're on a public ship in a busy server. Report the people when you see them, do not hesitate.
(Another thing, I'd suggest using a Stormchaser, Fortune Hunter, etc. ship. A lot faster, and the extra 1-3 knots could mean not reaching port or reaching it)