Hi Les. Does this help? The first time you use V:1 and V:2 add the 'cleff=treble' line.
For subsequent lines just use V:1 and V:2.

  T:Planxty Irwin
  C:Turlough O'Carolan
  Z:
  Q:1/4=112    %Tempo
  M:3/4    %Meter
  L:1/8    %
  K:G
  V:1 clef=treble
  d2|: g4 f2|e3 f g2 | d4  c2 | B3 A G2 |
  V:2 clef=treble
  g2|: b4 a2|g3 a b2 | f4  e2 | d3 c B2 |
  V:1 
   c4  A2 | B2 c2 d2 | G2 B3 c | B4  d2 | 
  V:2 
   e4  c2 | d2 e2 f2 | B2 d3 e | c4  f2 | 

Incidentally I'm doing this in a text editor. I never got ABC Navigator to work in Linux so I check the code in an online ABC player.