Like a number of work shanties and forebitter shanties, Poor Old Man, (also known as Poor Old Horse or The Dead Horse Shanty), is apparently featured in Assassin's Creed games.
As Eb Barnacle points out work shanties were sung 'a cappella', and purists would never accompany them on any instrument.
I am not a purist however and do sing some with guitar accompaniment.
I include lyrics and chords on screen with all my videos where applicable, though apparently these only work on PCs, not on other devices such as iphones, tablets etc.
Here is a link to my version of Poor Old Man:
Poor Old Man (Including lyrics and chords)
and here is a link to the forebitter song Poor Old Horse
Poor Old Horse (Including lyrics and chords)