In all this long thread, no-one seems to have made what seems to me one obvious suggestion as to a possible meaning: based on the well-known fact [cf Bonnie Bunch of Roses-o] that Bunch·Of·Roses was a nickname for redcoats in Napoleonic times, could not the crew of a merchantman being used as troop-carrier have been telling the soldiers maybe wandering the decks for some air to get back down below [hence 'Go down'], out of the way, & not obstruct them by crowding the decks while they were busy hauling — the 'Blood-red' being an aphetic [demanded by the rhythm rather than as bowdlerisation] for 'You blood[y] RedRoses': so that the meaning would be, "We're busy doing our job hauling here & you are obstructing us, so get back down below out of our way, you bloody soldiers!"?

Just a thought...