The 'Minches' is an area off the west of Scotland......see here... https://sac.jncc.gov.uk/site/UK0030393    Si I would suggest that this has at some stage been mis-written as 'Minch is'. When I used to sing this in the 1970/80s...these are the words I used then.

Heel ya ho boys, let her go boys,
Swing her head round now all together.
Heel ya ho, boys let her go, boys;
Sailing homeward to Mingulay.

What care we tho' white the Minches
What care we for wind or weather?
Let her go, boys! Ev’ry inch is
Sailing homeward to Mingulay.

Wives are waiting by the quayside,
Wives are waiting for break o'day o
Swing her round boys! And we'll anchor,
Before the sunrise on Mingulay.

Heel ya ho, boys; let her go, boys;
Swing her head round, now all together.
Heel ya ho, boys and we'll anchor ,
By the sunrise on Mingulay.