An 11-inch pivot-gun on its revolving carriage was served by 24 crewmen and a powderman.
Half the men composing a gun's crew, excluding the powderman or Boy, are to be Boarders.
To reduce from 20 men and powderman to 16 men and powderman, omit four next highest numbers.
To reduce from 24 men and powderman to 20, omit four highest numbers.
powderman returns spare powder and passing-box to the magazine.
If the powderman is disabled the highest number takes his place.
An explosives expert: That's powder-man in the trade (1980s+)