I know it's a ridiculously old thread but in case anyone is interested I reckon : Standard tuning : capo on 3rd then it's basically the old Am (Cm) to G (Bb) with some C (Eb) thrown in (as below) - & that seems to be about it - one of the most common chord sequences in folk music really - works for The Unquiet Grave & others too

The (Am) night that I was (G)married
And (Am) lay in marriage (G) bed
Up (Am) came a bold sea (C)cap (G)tain
And (Am)stood at (G)my bed (Am)head
Saying, (C) "Rise, arise, new (G)wedded man
And (Am) come along with (G)me
To the (Am) lowlands of (C)Hol (G)land
For to (Am) face your (G) ene(Am)my"

Pretty simple stuff really but (imho) what makes it so powerful is (as always) Carthy's exquisite singing & powerful delivery (& the lovely relaxed tempo)