Do you know?

I remember a young hero getting teamed up with a warrior (that is discovered to be a woman latter on) and is sold out by HER king. They sail on a ship to rescue a small boy (a young king Arthur?) left on a prison island. The boy finds a sword... I also remember a old man with the boy (Merlin?) and he is set on a swinging yard arm to hang over a cliff. The hero's climb up the cliff to rescue them and slay the evil guards and bad guys. there are only a small amount of hero's... and all the guys trip out over how bad ass the warrior woman is.
what is the name of this movie?