If it is not affecting your fathers job or the positive attention he is giving to you then it is not really an issue. Marijuana is a lot safer than beer and other alcohol related products. It has been recognized in many medical communities to be a very positive force in pain control. American medical association for one.

For some information that isn't skewed by bad indoctrination and is based on real science visit some of the sites below:

Http://Norml.com
http://www.aclu.org/drugpolicy/index.html
http://www.drugsense.org/
http://www.leap.cc/
http://www.mpp.org/

I believe you should confront him in a loving way and focus upon how his behavior is effecting you. He needs to hear and understand your unhappiness with his behavior. You don't say how old you are but you are very mature and brave for wanting to deal with your dads behavior. I'm sure it cannot be easy for you. Also can you talk to your Mom about it? if not, please find a trusted family friend or counselor if your Dad does not respond positively. Make sure you talk to someone-starting with Dad. Even if Dad responds positively, your family still needs some help. Please look into counseling. My prayers are with you.