Osprey-class sloop

The original design, as fitted to the first two ships of the class, was a single-expansion returning-rod steam engine, but the power was insufficient, and they failed to meet the contracted speed. Wild Swan and Penguin were re-engined after their first commission to match the better engines in the rest of the class.[1] In the final installation, power was provided by three cylindrical boilers, which supplied steam at 60 pounds per square inch (410 kPa) to a two-cylinder horizontal compound-expansion steam engine driving a single 13-foot-1-inch (3.99 m) screw. The power varied wildly from ship to ship, with Penguin generating only 666 indicated horsepower (497 kW) and Pelican managing nearly twice as much, at 1,056 indicated horsepower (787 kW). Because of this, top speeds ranged between 10 and 12 knots.[1][Note 1]

They were armed with two 7-inch (90cwt) muzzle-loading rifled guns on pivoting mounts, and four 64-pounder muzzle-loading rifled guns (two on pivoting mounts, and two broadside). Four machine guns and one light gun completed the weaponry. Wild Swan and Pelican later had the muzzle-loading guns replaced with two 6-inch (81cwt) breech-loaders and six 5-inch (31cwt) breech-loaders.[1]

All the ships of the class were provided with a barque rig,[1] that is, square-rigged foremast and mainmast, and fore-and-aft sails only on the mizzen mast.

They had a complement of approximately 140 men.[1]

The design was revised in 1877 and nine ships were ordered to a modified version, the Doterel-class sloop. Identical in many respects, the Doterels lacked the graceful clipper bow of the Ospreys, although they benefited from more power.[1]