Maritime Art - Drawing Seafaring Themes
Drawing Ships at Wet Canvas
This tutorial has lots of useful information about the structure of ships and some of the details you need to know to draw them well.
John Singer Sargeant - Sketch of a Sailboat
This sketch is a superb example of accurate observation combined with precise yet vigorous drawing technique. Notice the use of directional hatching to shape the sail, the strong sense of perspective, and the deft but light handling of the rigging.
Ship Reference Photos
An extensive collection of reference images of historical military vessels.