Readers of the Norton edition will notice a surprising number of left-handed sailors on the cover. Even the marine is firing his musket as a lefty, a dangerous practice since it places the flintlock and flashpan directly in front of his eye. Those with the Harper Collins edition have none of these problems, and their hawsers are not cable-laid, because their cover is as Geoff Hunt painted it, with the guns on the starboard side. The Norton cover is reversed to better accommodate the title block.
The scene is looking forward, from the main deck in the middle, or waist of the ship. The foremast and a head sail (jib or forestay sail) are visible through the smoke. In this part of the frigate, the upper deck is not planked over, except for the narrow gangway over at the side, on which the marine is standing. Normally, the ship's boats would be stacked on the large beams overhead, but they are probably being towed astern for the battle to avoid the hazard of splinters. Now only a spare spar is lashed in place. The dark shape far forward is the galley stove, just under the break of the forecastle.
There probably should be more men in the gun crews, but that would overly crowd the scene. The fellow in the red bandana is the gun captain, sighting the gun and preparing to pull the lanyard attached to the flintlock mounted on the gun. Two other crew hold crowbars for traversing the gun from side to side if necessary. They will also haul on the side tackles to run the gun out after loading. Another man is holding a leather cartridge case for carrying the cloth wrapped powder charge from the magazine below to the gun deck. A matchtub is by his foot. The train tackle leads from the rear of the gun carriage to a ring bolt in the deck amidships. It is used for running the gun in fully for loading.
There is nothing apparent to me to suggest whether this is meant to depict the Shannon in battle with the Chesapeake, or the earlier battle aboard the Java. I asked Geoff Hunt about this scene, and he replied neither; it was meant to be a generic frigate engagement, not a particular battle.