Arrrrrgh! I have only a passing interest in "Sea Shanties." I spent 20 years in the Navy. As chaplain, it worked out that about half of that time I happened to be assigned to Marine Corps Units of several different types but I also spent a fair amount of time at sea.
Shipboard life is vastly different than it was in sea shanty days, although some things about life at sea will never change. With the coming of the industrial revolution and the mechanization of much of the work done on ships, sea shanties have all but disappeared.
Ghostly relics of the shanty are now only performed as some type of entertainment or study; and the meaning, pain, and sweat behind the shanties is gone. The sea shanty has now morphed into a form of entertainment. It is and always was an art form. But they were originally work songs. It is interesting to notice how the form of sea shanties has changed because of this shift from work to entertainment. The original form as a work song has been preserved and can still be found, but one must look for strict shanty purists to find it. Most likely one will find a studio, mixed, and enhanced form of the shanty. Don't get me wrong. They make nice songs; but originally, they were not nice songs about nice situations. They were song by sailors or whalers hard at work and the song kept the pace and allowed these men to not think about the difficult jobs they endured.
To see an example of what I mean, listen to the hauntingly beautiful "Lowlands Away" by Ali Darragh.
Then there is what might be a more authentic version of this song by the shanty group called: "Pressgang Mutiny"
'Lowlands Away" is probably a "rowing" shanty although it could be a "capstan" shanty. The difference is of course in the beat. Rowing shanties have a definite beat which naturally determines the rowing rate. "Capstan" shanties have a constant flow which reflects the constant revolving toil of the capstan as it is rotated to weigh the anchor or hoist a sail. As in this picture: There were also shanties called "heaving" shanties. These were used as sailors heaved on a line for any reason but usually to raise rigging. Here is a link to the one called "Blood Red Roses" A great example of this shanty is also seen in the 1956 version of "Moby Dick" as the Pequot gets underway. Oddly enough some of the best examples of genuine sea shanties are found in this 1956 "Moby Dick" movie but the particular sea shanties shown in the movie probably were not used much in the time frame of the story by Herman Melville.
Another good 'heaving shanty":
Other Shanties existed called Foc'sle shanties. Here is an example of one
Foc'sle shanties were work songs but they were also entertainment songs. Sailors would sing these while doing menial labor, bright work, or housekeeping [called "field day"], or any monotonous job.
In general sea shanties are folk songs. What sets them apart from what we typically refer to as folk songs is that the folks who composed and sang these songs were sailors or whalers. Shanties are hugely influenced by Celtic and European roots, as well as African. They come from the time frame of many of our "Old timey" songs.
They deal with the full range of life subjects, just like "old timey" music and blue grass. These themes may range anywhere from unfaithful wives to faithful wives, from murder to birth, death, life, sex, (or lack thereof), beautiful girls, not so beautiful girls, joy, sadness, or anything experienced in life. The lyrics are often inappropriate by our standards. But, don't judge. This is music composed and sung by hard men during hard times doing hard work often against their will.
The music is fairly easy to transcribe and memorize. Many forms of notation are available. One can easily make up their own lyrics. Consequently, these songs have dozens of verses. Listen to a few. Enjoy them. You will visualize sails, rigging, masts, decks and lines (ropes). Close your eyes and you will feel the deck rise and fall and smell the salt sea air.