Combine the beer, vinegar, peppercorns, garlic and bay leaves with 6 cups of water in the bottom of a 32-quart tamale steamer or water bath canner with a rack about 4 inches up from the bottom over high heat. Place the live crabs in the freezer until the water comes to a boil: They’ll be easier to handle and less likely to fight.
Reserve ½ cup of Chesapeake Bay seasoning to serve at the table, and mix the salt into the remaining cup. When the water boils, place a layer of 6 crabs right-side up in the pot, and sprinkle with ¼ cup seasoning. Continue layering the remaining crabs and seasoning, ending with the fourth layer. Cover and steam for 25 minutes. Remove the pot from the heat source, and let it cool, uncovered, for 10 to 15 minutes. Lift out the steaming basket or canning rack and transfer the crabs to a table covered with butcher’s paper or newspaper. Pass around the melted butter and the reserved seasoning.