Sea shanties (singular "shanty", also spelled "chantey"; derived from the French word "chanter", 'to sing') were shipboard working songs. Shanties flourished from at least the fifteenth century through the days of steam ships in the first half of the 20th century. Most surviving shanties date from the nineteenth and (less commonly) eighteenth centuries.

In the days when human muscles were the only power source available aboard ship, sea shanties served a practical purpose: the rhythm of the song served to synchronize the movements of the ship workers as they toiled at repetitive tasks. They also served a social purpose: singing, and listening to song, is pleasant; it alleviates boredom, and lightens the burden of hard work, of which there was no shortage on long voyages.

Most shanties are "call and response" songs, with one voice (the shantyman) singing the line and the chorus of sailors bellowing the response

• Long-haul (also called "halyard", "long-drag", or "single-pull") shanties: Sung when a job of hauling on a rope was expected to last a long time. Usually one pull per verse, to give the men a chance to rest. Examples: "Hanging Johnny," "Blow the Man Down."
   
• Short-drag (also called "short-haul", "sheet", or "hand over hand") shanties: Sung when a job of hauling on a rope was expected to be quick. Two or more pulls per verse. Examples: "Haul Away, Joe," "Blow the Man Down," "Drunken Sailor."
   
• Capstan Shanties: Raising the anchor on a ship involved winding the rope along a giant winch, turned by sailors walking around it.   
  Capstan shanties are anchor-raising shanties. They are typically more "smooth" sounding than other types (no pulling required) and, unlike many other types of shanties, frequently have a full chorus in addition to the call-and-response verses. Examples: "Santianna", "Paddy Lay Back," "Rio Grande (Away Rio)," "South Australia," "John Brown's Body," (adapted from Army marching song).
   

  Ships' capstans were traditionally manually operated —  consisting of a shaped wooden drum with handles  inserted into the rim, at which men could push or pull.  http://en.wikipedia.org/wiki/Capstan_%28nautical%29

  Naval anchor incorporated  into HMAS Canberra(1927)  memorial, Canberra,  Australia

   

• "Stamp-'n'-Go Shanties": were used only on ships with large crews. Many hands would take hold of a line 'tug-of-war' style and march away along the deck singing and stamping out the rhythm. Alternatively, with a larger number of men, they would create a loop -- marching along with the line, letting go at the 'end' of the loop and marching back to the 'top' of the loop to take hold again for another trip. These songs tend to have longer choruses similar to capstan shanties. Examples: What do you do with a Drunken Sailor, Roll the Old Chariot. Stan Hugill, in his Shanties from the Seven Seas writes: "(Drunken Sailor) is a typical example of the stamp-'n'-go song or walkaway or runaway shanty, and was the only type of work-song allowed in the King's Navee (sic). It was popular in ships with big crews when at halyards; the crowd would seize the fall and stamp the sail up. Sometimes when hauling a heavy boat up the falls would be 'married' and both hauled on at the same time as the hands stamped away singing this rousing tune."
   
• Pumping Shanties: All wooden ships leak somewhat. There was a special hold (cargo area) in the ships where the leaked-in water (the bilge) would collect: the bilge hold. The bilge water had to be pumped out frequently; on period ships this was done with a two-man pump. Many pumping shanties were also used as capstan shanties, and vice versa, particularly after the adoption of the Downton pump which used a capstan rather than pump handles moved up and down. Examples include: "Strike The Bell," "Shallow Brown," "Barnacle Bill the Sailor," "Lowlands." See Leave Her Johnny Leave Her.
   
• Fo'c's'le (Forecastle) Shanties: Shanties sung for fun. Example: Rolling Down To Old Maui. As these were not sung during work, they are sometimes not referred to as "shanties", but rather as forebitters or simply as sea songs.
   

  The above categories are not absolute. Sailors could (and did) take a song from one "type" and, with necessary alterations to the rhythm, use it for a different task. The only rule that was almost always followed was that songs that spoke of returning home were only sung on the homeward leg, and songs that sung of the joys of voyaging etc., were only sung on the outward leg. Other songs were very specific. "Poor Old Man" (also known as "The Dead Horse") was sung once the sailors had worked off their advance (the "horse") a month or so into the voyage. Leave Her, Johnny Leave Her (also known as "Time for Us to Leave Her") was only sung during the last round of pumping the ship dry once it was tied up, prior to leaving the ship at the end of the voyage.