All together now:
Hands out of the rig of the day clear off the upper deck, close all screen doors and hatches, up all deadlights.
A pipe made just prior to going to sea, or, whilst at sea, just before comming into harbour. Makes the ship look tidy, as Jack and Jenny are confined downstairs.
Rumour has it that on more than one occasion this pipe has been made by a very inexperienced Bosun's mate trying to pronounce the acronym, rather than each individual word, much to the disgust of those on board the subject ship, and to the great delight of anyone nearby in the dockyard.
See also: Special Sea Dutymen, Harbour Stations.