The frigate's cannon attack is back to its original crew requirement, and the Impossible was raised from 22 to 30 (although still less than its original 40.
The Audacious was given a smaller cannon size to provide some separation between it and the Inevitable, whose text says it has bigger guns than the Audacious.
I did not spell it out in the supplement, but I envisioned the following cannon sizes:
Small: 4-pound cannon; 1 crew per cannon
Light: 8-pound cannon; 2 crew per cannon
Heavy: 12-pound cannon; 3 crew per cannon
Full: 24-pound cannon; 6 crew per cannon
Essentially, a cannon needs 1 crew per 4 pounds of its shot. I rounded up a bit on the big ships as overhead, and the steamships need a few extra to turn the turret.
In real life, this would be too few crew to fire every two minutes, but I felt it fit best within the system. It leaves space for the crew running the ship, and the officers, with a few spare crew to man the guns if the ship takes a few hits; unless your a using a cutter. One strike on a cutter, and the captain is going to have to start juggling crew.