It does not seem as though there were shanties actually written/published by someone with a political motive. At a time when most music was made by people for themselves, it could be expected that sailors would sing for entertainment, and they sang popular songs. But sea shanties were used to coordinate the crew, and seemed to have been either passed along or improvised by one man, the shantyman. As Capt Robert Adams noted,

THE songs of the sea offer a field for research, and one who could trace the origin and use of some of them would doubtless discover interesting, romantic histories. No information can be obtained from sailors themselves on this point. No one knows who their favorite "Reuben Ranzo" was, or whether "Johnny Boker" ever did what he is so often requested to "do," nor can any one say more concerning the virtues and vices of "Sally Brown" than is declared in song.

Sailors' songs may be divided into two classes. First, are the sentimental songs sung in the forecastle, or on the deck in the leisure hours of the dog-watch, when the crew assemble around the fore-hatch to indulge in yarns and music. Dibdin's songs, which the orthodox sailor of the last half century was supposed to adhere to as closely as the Scotch Presbyterian to his Psalter, are falling into disuse, and the negro melodies and the popular shore songs of the day are now most frequently heard. The second class of songs is used at work, and they form so interesting a feature of life at sea, that a sketch of that life would be incomplete without some allusion to them.......

Great latitude is allowed in the words and the shantyman exercises his own discretion. If he be a man of little comprehension or versatility, he will say the same words over and over, but if he possesses some wit, he will insert a phrase alluding to some peculiarity of the ship, or event of the time, which will cause mouths to open wider and eyes to roll gleefully, while a lively pull follows that rouses the sheet home and elicits the mate's order "Belay!" A good shantyman is highly prized, both by officers and crew. His leadership saves many a dry pull, and his vocal effort is believed to secure so much physical force, that he is sometimes allowed to spare his own exertions and reserve all his energies for the inspiriting shanty.

Adams wrote his own memoir a few decades after Richard Henry Dana's Two Years Before The Mast had recounted the appalling working conditions and abuse suffered by sailors, and at a time when the British merchant marine was beset by scandals about "coffin ships". Adams was a devout Christian who believed that he had always gotten much better performance from his crews by treating them with care and respect ( and some evangelizing ). So, it's to be expected that he would have been a fan of sea shanties.

Adams, Robert C. ( 1879) On Board the Rocket. Lothrop, Boston.