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Which I do. Also I'm level 9, and I found some heavy weapon boosting items, so I'm using an Estoc. Badly.

Anyway, I'd beaten the Blue Bird down to just above zero crew. You cannot kill the entire crew, and the ship never surrenders without a fight. So I fought the captain, and lost. Reload. Lost. Repeat several times. Once I got him down, but he talks, recovers, and fights you a second time. Finally I decided to sink him and move on. Oh. Except I never carry round or explosive shot. Damn. Reload in town, buy explosive shot, restart the fight, hm, he appears to also use whatever shot you're using, my ship is really getting decimated here. I put some distance between us, and told my galleon to board to make them move closer. shooting him up again, told the galleon to attack instead of boarding, and then ..

WHAT, MY GALLEON HAS JUST BEEN SUNK, that was my galleon .. full of crew .. and one of my 3 best Navigators ... wait, the navigator's still there, and HES CAPTAINING THE BLUE BIRD! The navigator boarded them, took the ship, and sunk the galleon.

I saved just in case, but now I've reloaded back in town, bought back the plundered galleon I'd sold before, loaded it full of crew, sold the cannon, put in nominal food and rum, but loads of weapons and medicine, now I'm going back, and sending that ship straight over to board while my main galleon and I pepper them with explosive or bar shot from far away.