I always understood, 3 major threads of Chanties,

1 Work songs to coordinate a crews efforts. Example "Haul away Joe"

2 Forebitters or entertainment songs. Example "Flash Packt"

3 Seamen or Pilots Memonics Example "Spanish Ladies"

Though I have no doubt that some more knowledgable Catter will have a more precise and explanatory explanation.

In the meantine try CLICK HERE

I hope this works !!

Gareth