The shields or pavises along the side of the ship are a pavisade which is
A protective barrier made up of shields bearing the arms of those on
board placed along a vessel's sides.
The Wikipedia Pavise article has a slightly more detailed description:
a decorative row of shields or a band of canvas hung around a sailing
vessel to prevent an ...
As far as I know, "Instructions for training a ships crew in the use of arms in attack and defence" by Lieutenant William Pringle Green, is the first book on how a crew of the Royal Navy should train with swords and guns. And Also how should they defend their ship in case of boarding or to board an enemy vessel themselves.
The year of publish is 1812, so ...