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Post-ship was a designation used in the Royal Navy during the Age of Sail to describe a ship of the Sixth Rate (see rating system of the Royal Navy) that was smaller than a frigate (in practice, carrying fewer than 28 guns), but by virtue of being a rated ship (with at least 20 guns), had to have as its captain a Post-captain rather than a lieutenant or commander. Thus ships with 20 to 26 guns were post ships, though this situation changed after 1817.

Sea officers often referred to the post ships as frigates though technically they were not frigates. The vessels were frigate-built, with traditional quarterdecks and forecastles, but, unlike true frigates, they lacked an orlop platform amidships. They had a high center of gravity, which made them slow and unweatherly, but they were seaworthy. In peacetime the Royal Navy frequently used them as substitutes for frigates, especially in distant foreign stations.

Unlike other uses of the term "ship" during this era, "Post-ship" in itself implies nothing on the rig of the vessel; however, all Sixth Rates were in practice ship-rigged, i.e. were square-rigged on three masts.

For an example of a Post-ship see: HMS Camilla. She was one of ten Sphinx class Sixth Rate Post-ships built during the 1770s.

Sources

• Winfield, Rif (2007) British Warships in the Age of Sail 1714 - 1792: Design, Construction, Careers and Fates. (One of a series dealing with British sailing warships; other volumes cover 1603-1714 and 1793-1817) Seaforth Publishing. ISBN 978-1-84415-700-6.
• Winfield, Rif (2005) British Warships in the Age of Sail 1793 - 1817. (London: Chatham), p. 226.