There are two chanteys (that I know of) which contain a reference to "long tail blue", viz.:

ONE MORE DAY
Get out yer long tail blue, my Johnnie
One More Day
Make yer port and take yer due, my Johnnie
One More Day.

and

RANZO RAY
We're putting on our long tail blue to dance the girls around...

I've not come across this expression in any of the reading I've done, only in the lyrics of these two songs. What does it mean?

Jerry