Acholic father , child abuse?

Okay so , I am 17. I live in Maryland. And my father is an acoholic. He has put me and my grandmother through **** over the course of my life. My mother lives in new york for the record. and I dont have a relationship with her. She use to send me cards all the time but he would put "return to sender" and he has custody of me. but Anyway, he still lives here with his mother, (my grandmother) and she has raised me my whole life. He hasn't done anything for me. My father doesn't let me out the house AT ALL. Im always stuck in the house because if i ever leave he threatens to kill my cat. He has threatened to shoot me and my grandmother before and has called us bitches and sluts. Keep this in mind I just recently graduated. and im a good kid. I dont do drugs. my grades are good. and when i turn 18 which is october 13th. i plan to move with my cousins start college and get a full time job.. But I am also concerned bout the safety of my grandmother. Im afraid he might physically harm her when I am gone. This past day i went to the grocery store with my grandmother, and he put me on punishment for 2 months. and then another month for messing up magnets on the fridge. I tried to have a decent convo with him but he just said leave me alone and i dont wanna talk to you. Some incidents were worse and he has punched walls and broken down doors before. Like I said he has lived in this house his whole life. and he has me and my grandmother terrified. he doesn't pay bills but he works. just to buy his beer and cigarettes. Im tired of going through this with him. He never hit me just for the record. but as far as emotional abuse he has done that. he has even made a homemade paddle out of wood and its about a inch long and says "lindseys paddle" I want to get the police involved somehow because im suffering. He doesn't like people coming over here at all. and he has alineated me and my grandmother from the rest of our family and everyone really. I just dont know what to do anymore,, So if you can help please do!! it would mean alot.