How do I tell my dad I have an eating disorder?

My mom found out about my bulimia but simply does not understand. She's convinced that I am just depressed but I am not. I am not sad, I go out with my friends, I don't want to die. I explained this to her but she still thinks I am.
My dad does not know about my eating disorder yet. I need my dad to support me and help me get treatment for this. But I don't know how to do this since he is male and might not understand as well.

Look at this website:

http://www.somethingfishy.org

There is a section on there that helps family/friends know how to deal with those who have eating disorders. Might want to have him look at that after having a talk with him about how you feel about food. I would say just be honest with him.

Talk to your pediatrician, maybe he could speak to your parents for you. Even if it's depression that your mom suspects you have you are still in need of treatment.
Couple suggestions:
Write him a letter/note simpyly saying you need his support and are struggling with food?

Maybe if you have a meal together tell him that you have issues with the food infront of you? Strike up a conversation with him about how he feels about food/diet/body image/size?

Ask him if he's had any experiance with someone he knew/love suffereing from an eating disorder?

If you are afraid of his initial reaction you might want to tell him while you are driving in the car, so he has to stay focused on the road. Tell him that you're suffereing and your mother isn't helping at all and you're hoping to find the support you need in him.

Good luck.