Yes, semi-submersible, ships of the line carried a lot of people, however, five hundred seems a little bit stretched even for a man-o'-war. (Not seventy-five, of course.) I was thinking of a different thing, that this kind of exaggeration seems quite in the line of shanties - take the Irish Rover, for one:
On the Fourth of July, 1806
We set sail from the sweet Cobh of Cork
We were sailing away with a cargo of bricks
For the Grand City Hall in New York
'Twas a wonderful craft
She was rigged fore and aft
And oh, how the wild wind drove her
She stood several blasts
She had twenty seven masts
And they called her The Irish Rover

We had one million bags of the best Sligo rags
We had two million barrels of stones
We had three million sides of old blind horses hides'
We had four million barrels of bones
We had five million hogs
six million dogs
Seven million barrels of porter
We had eight million barrels of old nanny goate tails
In the hold of the Irish Rover

http://www.sing365.com/music/lyric.nsf/The-Irish-Rover-with-The-Dubliners-lyrics-Pogues/07732FED8885095A48256A2600145F4B