HMS Isis launched in 1819 was ordered in 1811 as a 50-gun two-decker of the fourth rate Salisbury class, but was redesigned while building, being lengthened on the stocks by 11 feet, and cut down by one deck to produce a spar-deck frigate

Frigate

A frigate is any of several types of warship, the term having been used for ships of various sizes and roles over the last few centuries.In the 17th century, the term was used for any warship built for speed and maneuverability, the description often used being "frigate-built"...

, that is, to carry extra guns on the spar deck which linked the forecastle

Forecastle

Forecastle refers to the upper deck of a sailing ship forward of the foremast, or the forward part of a ship with the sailors' living quarters...

 to the quarterdeck

Quarterdeck

The quarterdeck is that part of a warship designated by the commanding officer for official and ceremonial functions. In port, the quarterdeck is the most important place on the ship, and is the central control point for all its major activities. Underway, its importance diminishes as control of...

.

It was then intended for her to have carried 58 guns as shown in the table, but this weapon 'fit' was amended on 3 June 1823 to complete her as a 50-gun frigate with an unarmed spar deck, and she was later reduced in 1830 to a 44-gun frigate carrying twenty-six 32-pounder guns on the upper deck, twelve more 32-pounder guns on the quarterdeck, and two 32-pounder guns on the forecastle together with two 8-inch shell guns.