I don't usually post in this section Bob but I saw an unanswered post and thought I would read it. I am an alkie myself but I can see what you are going through.
Why don't you talk to your dad and tell him what you are thinking and how you feel. I am sure that he loves you and wants to be there for you but the alcohol has control over him.
You may be the link that he needs to beat his addiction.
It sounds like he has tried and slipped a few times and this is not unusual.
Suggest he comes here and reads and joins this forum. We help each other get better so we can be the fathers and mothers we want to be.
Good luck and be strong and help him. He sounds like he wants to be the father you want him to be.