That entire verse is gibberish - what has a "mountain pass" to do with sailing on the Grand Banks? This version makes more sense:

So now it's reef and reef, me boys
With the canvas frozen hard
And it's mount and pass every mother's son
On a ninety-foot tops'l yard

http://www.kinglaoghaire.com/site/lyrics/song_656.html

Lyrics posted on the internet are often full of misheard or misunderstood words - this is particularly the case when the words are transcribed from a recording by someone who may not be a native English speaker. Dick Gaughan has an entertaining example on his website of a song mistranscribed from Scots which makes absolutely no sense at all. Unfortunately the errors then get reproduced.