Here is, I hope, some help off the sheet music, which it turned out I had. With a few caveats. Being Brecht/Weill the music is very sophisticated, with all kinds of 9ths and 13ths, etc. on the piano; and the version I have located is a guitar version by John W. Duarte (Brecht/Weill Songalbum: Music Sales G.m.b.h. (copyright date unknown). I have edited and condensed the chords, but I think they are not quite right for pop. guitar (if that is what you are after). It may be that Steeleye Span used a simpler version (I don’t know their version) or in some other keys. I have also (for lack of time) just given the basic structure. The chord changes are so obvious that you shouldn’t have difficulty figuring out where they go. In the verses the chords usually wander back and forth in sequence, e.g. Cm/Cm9/Cm/Cm9 until the double slashes for the next main change.
Cm/Cm9// A7/Dm// Aflat/Gflat7Eflatm/Gflat/Aflat/gflat7/eflatm/gflat7/aflatm// Eflatm/Aflat13// Bm/fsharp7/Em7/Daug/Em7/Daug//
And the ship, the Black Freighter...
(repeat verses, and then the last verse repeats to the following, and then goes on...)
And they’ll say, kill them now or later... Aflatm/Eflat m/Bm/Eflatm/Bm/G7// Hoppla! /Fsharp9/
And the ship.... Bm/Fsharp/Em/Fsharp.