Sycho,

As long as you have a laminate sail (with a Mylar or smooth plastic surface) the world is available for graphics on your sails - there are no design limitations over what you put on your hulls. However, you do need to pay more attention to the quality of the vinyl when you are applying it to sails. Note: It's difficult to get anything other than paint to stick to a dacron sail.

A little care needs to be taken to make sure that your sign shop is supplying you with a top quality vinyl for a flexible application like a sail - 3M and Avery make the best and most popular (and most expensive). MacTac is pretty good too. Vinyl is rated by outdoor life and as a generalization, the longer outdoor life rating, the thinner and stickier the vinyl is. It is especially important that the vinyl be thin for the sail in order to stretch and compensate for seams and stitching lines. The best you can get is a 7 year outdoor rating but you can expect it to last longer in this kind of application. Don't use anything less than a 5-year vinyl for sails (typical ratings are 'temporary', 3yr, 5yr, & 7yr). One other thing to keep in mind is that metalics, reflectives, and metalflakes don't last as long as solid colors.

Application is really no different than you need to keep the sail stationary and on a flat surface during application (my pool table works great for this!). Let me know if you need more detail (you probably know this already) but

A) align graphic in place with backing paper still on
B) make a masking tape hinge at the top of the graphic between the application tape (that covers the graphic) and the sail.
C) flip the graphic upside down using the masking tape hinge.
D) spray the area on which the graphic is to be applied with a solution of 1 quart tap water and 4 - 10 drops of liquid clothes or dishwashing detergent (just enough to make a few suds). Be carefull not to wet the backing paper or any other part of the graphic.
E) Peel away an inch or two of the backing
F) Rotate the graphic back to an upright position and rub down the exposed adhesive as you continue to peel away the backing from underneath.
G) rub down the top with a squeegie or rolling pin to adhere the graphic well.
H) wet the application tape (if it is the masking tape- like variety) - this makes it soft. If it is the clear plastic variety, skip this step.
I) gently peel away the application tape.

Voila! a well aligned, bubble-less graphic!