Perhaps this thread should be given a sub-title : Bag o' Worms! But enquiring minds need an answer.
I have been generating MIDI's recently without any real consideration of tempo.
The standard musical notation for tempo is the symbol for a note, e.g. a quarter note, equals (=) a number e.g. 88.
The abc notation has provision to accomodate such, viz. Q:1/4=88.
However, seldom do the published chanties have this information.
Doerflinger does, sometimes.
Bone does for the most part, but then he also uses the term "andante", et. al.
Colcord gives none whatsoever

Since chanties were "work" songs, the tempo would have been set by the nature of the work at hand. That is, say marching around the capstan.
However, even in that case, there would have been a moderate tempo while bringing the ship to the anchor 'til the cable was "up and down", then somewhat slower to "break 'er out", and faster to bring the anchor up to the hawse.

Reuben Ranzo is cited in most Chanty books.

As noted, Colcord has none.
Bone has 1/4 note = 108
Whall says : Brisk
Doerflinger has 1l4 = 88, and also :Moderately
Haswell has none
Hugill has: Strong and Steady
Bullen has none, although adverbs for other tunes
Huntington has none
Shay has none
Harlow has: Marcato
Terry says: With unction
L.A.Smith give none, although adverbs for others
Alden gives: Allegro