Another suggestion is going to the Lester Levy site (http://levysheetmusic.mse.jhu.edu/) and checking out their covers ( go to browse the collection and choose cover art only). I got a great many of the graphics for my page here. I cropped the parts I wanted and make them black and white in Paint Shop Pro (a cheap but great shareware program).

You can see one I took here. As I recall there were some other fantastic sailings ships.

The advantage of these is they are public domain.