Any advice on how to gank with nunu

I've been playing nunu a lot because I like him and his objective controll play style but I feel like his ganks are really really bad and I get flamed when a lane loses and I can't do enough to help them, any advice on how to improve his ganks? Maybe it's the way I gank that makes it awfull or something I ussally just go in slow them and bloodboil my allie after that you can't really do much. 90% of the time I just constantly annoy the enemy jungler because my ganks are just awfull. I know hes ment to be a counter jungler but you can't just spend the entire time in the enemy jungle. Also, everytime I ult with him they just instantly cc me down or excape with ease.

Any advice?