Prized for their nautical images and folk art craftsmanship, “sailors’ woolies”—pieces embroidered by 19th-century sailors while on long voyages—are highly collectible today. These works, typically of British origin, often depict ships of the Royal Navy, with slogans or messages worked into flags flying on the ship’s rigging. What originated as a way for sailors to pass the time and send home a token is now a five-figure antique.

“What makes these works so charming is that each one is absolutely unique and personal,” says Paul Vandekar, a New York City-based dealer born in London into a family with a longstanding antiques business, Earle D. Vandekar (305 E. 61st Street, New York, www.vandekar.com, 212-308-2022,). His family’s business, which specializes in pottery and porcelain, began finding sailors’ woolies in households where they were looking at pottery, and another specialty developed.

The small woolies, which measure about 15-by-17 inches, were worked on backgrounds of cotton duck (carried on board to make sailor’s uniforms), potato sacks, or scraps of sailcloth while sailors were on board. Larger works, measuring 28-by-36 inches or more, were often made once a sailor had retired and was on land, according to Vandekar.

Sailors’ woolies date from the 1850s through 1890s, the end date coinciding with the advent of steam-powered ships and proper uniforms, eliminating two of the conditions that had fostered the craft: long sail voyages and having cotton duck on board for sailors to stitch their own uniforms.

“A sailor would get a piece of cloth and use charcoal to draw the outline of the image,” says Vandekar, “then he would work the image with wool threads.

Values for sailors’ woolies have doubled twice in the last 10 years, according to Vandekar. Small pieces today start at $4,000; larger pieces sell for $18,000 and up.