I have done the BB solo and it is possible. I have posted screenshots on here. You can also see them on my guilds web page under quests.
www.maraudersonline.com
I did the boss battle alone back when it was easy and again since the changes have been made. I never completed it with that pirate as I have been using it to train guild members and freinds on how to do 2 person BB's. We do a complete circle around the Goliath shooting broadsides and cannons in the water just to show how easy we could sink it if we want.
I make it everytime with 2 person battles and sometimes it takes me twice to do it alone. I have also been using the same pirate to try every different thing I have found on forums along with different ammo and have posted the results on our web page. It is too hard with a full crew doing the BB to find out what really works and what doesn't but being able to do it over and over alone and with one other crew member we have put it all to the test more than once. Any doubts? PM me and I will take you out and show you.