Hi bobbarker
Welcome to the forum. Dothi and Desert Eyes have the right suggestions. It is awkward to confront your dad about his drinking. He is trying to hide it, and somehow alcoholics always believe that they are successfully hiding the drink, so you are revealing a 'family secret', even though at this point it it a very large elephant in a not-very-large room. It is not your role to help keep that secret or hide that elephant - tell him you know, that it hurts you to see him destroy himself.
However, this won't make him stop drinking. You are laying it out that you won't help him keep drinking by ignoring the obvious and that you care for him. As you read about alcoholism, you will note that there are NO suggestions for ways to make them stop drinking. No intervention in the world will make stop an addiction to alcohol if they don't decide on their own to stop. It may seem strange, but the best message to send is "Your addiction and what it does to the dad I love is so awful that I have to set up barriers to keep it from making me insane."
Keep posting and tell us how it is going.