Dubloon

Dubloon is a vanilla currency. You can buy 1 Dubloon for 3 Diamonds from Beakeasy (penguin bartender in the vanilla Outpost), but only after completing the quest "Dreadwing the Penguin".

If you have 1 Dubloon in your inventory, you can hire penguin NPCs (making them your crew) by talking to them. Their profession is always "Soldier". If you agree to hire the penguin, 1 Dubloon is consumed.