I will be having a War Sloop, a War Frigate and a War Brig, and I have a tip for some of you wishing to purchase a War Brig (or any kind of Brig) and want to save some money...
Let's say you're like me and wanting to sell your War Galleon to buy a War Brig. You have all war ships, and you're at max gold, and willing to save some money. When the Brig comes out, sell the War Sloop, even if you want to keep it. Then buy the War Brig. Now sell the War Galleon, and buy back the War Sloop.
You can do this with any ship, but if you're far from max gold don't bother doing it. This allows you to keep more money than you would have if you'd just sold the ship you didn't want and then bought the Brig.