Well, that was in Irish Gaelic. The Clicky thing for that link is
There are some songs like Leis an Lurgainn which is a song about a boat which is rhythmically usable to row to at the right pace.
I don't think I've typed that up, but someone else may have.
One of the problems is, WHAT KIND of SHANTY? Besides that of WHAT KIND OF GAELIC.
My orientation is to the Scottish Gaelic, so if you are looking for Irish, I can't help. Will look into other songs which are Rowing type songs.
Another problem in a different light, is that most of the Gaelic countries were not major sea-faring lands at the hey-day of the Shanty (thought to be in the 18th century). Therefore there probably aren't many shanty type songs of the Capstan or Halyard varieties. However, for the "Fore-castle" - Fo'c'sle" type of story songs, you could probably sing many of the lonesome type songs. More of a ballad type, like Chi Mi Na Mor-bheana, would be used for that.
So, let's see
1 - What kind of Shanty? - Rowing, Capstan, Fo'c'sle, etc?
2- Which Gaelic? - Irish? Scottish? Manx?, etc?See if your friend has any preferences, and maybe we can give more information.
Meanwhile I'll see if some of my Gaelic friends and Shanty friends can give me more suggestions to pass on.