We've seen standard servos used to sheet in and sheet out using conventional RC servos. They can be fast and they provide very good control. But you need some pretty heavy duty torque for a surface sailing model with a mast over 24 inches. Go to IRCSSA.Org to determine the class you are interested in. The class is determined by the theoretical box you could put a fully assembled surface sailing model into.

My son is developing and selling the RCWindjammer; a model sail car with a mast 6' tall, an overall length of 44 inches and a beam of 38 inches which serves as a pretty good stable base in brisk breezes over 8 MPH. (He adds weights when the breeze goes over 12 MPH).

To control the sheeting (sail in and out) he has selected the HS-725BB from Hitec as the ideal sail winch. It has a drum and can pull or release about 12" of sheeting line. Here's a picture.

Wayne