Why hull fire caused heavy crew losses

How could a French ship lose such a high proportion of its crew?

British gunnery aimed into the hull, where shot killed crew members and helped prepare the ship for boarding.

French crews are described as firing on the upward part of the roll to strike masts and rigging. That suited disabling an opponent so their own ship could escape. British crews fired on the downward roll to hit the hull, inflicting casualties among the men inside. The comparison links aiming practice to the British intention to board and capture ships.