Actually, any type of acid will dissolve rust including lemon juice. Most sails made of Dacron or Polyester are resistant to acids. The lighter acids take longer but still work. And washing
the treated area with plenty of fresh water
is important so as not to affect other items like sail covers.
I have used nitric acid which takes it out in seconds but one must know the precautionary measures. Carpet cleaning
supplies carry a small bottle of Rust Remover
that works real good. But Rubber gloves and safety glasses
are a must when using any