His Majesty's Schooner Crab

Crab is a tiny schooner, mounting only two six-pound guns, crewed by a total of sixteen men and commanded by Lieutenant Harcourt. She is nevertheless one of Hornblower's fourteen sloops and schooners in the West Indies station. At the beginning of the novel, Hornblower makes Crab his flagship because his preferred frigate, Clorinda, is undergoing refit at the time.

Steam Tug

A steam tug is a small vessel with a powerful steam engine powered by coal or other combustibles. Their primary function was to assist other vessels or ships maneuver through difficult or restricted passages. The first successful steam ships were built circa 1807, and at the time of the novel, a steam tug would have still been something of a novelty. Although Hornblower views them as curious but useful machines, he can but little guess that they spell the doom of an entire profession...