The 8-pounder long gun was a light calibre piece of artillery mounted on French warships of the Age of sail. They were used as main guns on light ships of the early 19th century, and on the quarterdeck and forecastle of ships of the line. They were similar in design to the Canon de 8 Gribeauval.
8-pounder long gun Wikipedia
The 8-pounder was the heaviest of the light guns. Its light weight allowed it to be mounted on the upper gun posts of ships of the line, where the timber of the deck was too light to support larger guns; furthermore, it could be mounted relatively high without jeopardy to the stability of the ship, and could be installed at will at different positions. This made it useful as a chase gun, since its load packed enough power to damage the rigging of a fleeing enemy (if used as a bow chaser) or of a pursuing enemy (when used as a stern chaser).