Usually by the time you reach Aquila, you have so many companions that it doesn't even matter anymore where you put Catbeard on the Companion board. Sure, if he is second mate, he will probably have a 3% more chance to appear than the Companion at the bottom. If you like Catbeard so bad, I suggest you make him your first mate. Right now I have 10 companions, and this is the percentages from second mate to Lowest companion, 23, 16, 14, 13, 12, 11, 8, 6, 5. So when you reach Aquila, it might look something like this: 8, 8, 8, 8, 7, 7, 7, 7, 7, 7, 6, 6, 6, 5, 5. If you're a privateer, good luck getting Catbeard onto the battle board as second mate.