I also thought the song was by Calum MacDòmhnaill and Ruairidh MacDòmhnaill of Runrig - but at https://www.cpdl.org/wiki/index.php/File:Cearcall_A_Chuain.pdf the words are credited to Eòin Mac a' Mhuilleir and the tune to C & R Domhnallach (so we have three versions of their surname, McDonald, MacDhomhnaill and Dòmhnallach)

a few years ago, I copied the following lyrics with guitar chords, but I didn't write down the source unfortunately:

Tha sinn (D)uile air (Bm)cuan
Stiureadh (G)cuairt troimh ar (D)beatha
A' (Bm)seoladh geola (F#m)dhorch
Air (Em)chall an greim na (A)mara
Tha a'(D)ghaoth air ar (Bm)cul
Tha a' (G)gheol a' cumail (D)roimhe
'S cha dean (Bm)uair no an (F#m)cuan
Tonaisgh (Em)dhuinn (A)no ri(D)an

A' (D)mhuir tha i (Bm)ciuin
Tha i (G)fiadhaich tha i (D)farsainn
Tha i (Bm)alainn tha i (F#m)diamhair
Tha i (Em)gamhlasach is (A)domhain
O ach (D)sin tha sinn (Bm)dall
'S chaneil a(G)gainn ach (D)beatha
Tog an (Bm)seol, tog an (F#m)ramh
Gus an (Em)fhaigh sinn (A)astar (D)ann

Ach tha mi'n (D)duil, tha mi'n (Bm)duil
Nuair a (G)bhios a' ghrian dol (D)fodha
Chi iad (Bm)mi a' stiuireadh 'n (F#m)iar
Null a (Em)dh'Uibhist air a' (A)chearcal
Cear(D)cal a' chu(Bm)ain
Gu (G)brath bidh i a' (D)tionndadh
Leam gu (Bm)machair geal an (F#m)lar
Far an (Em)do thoi(A)sich an (D)la
D-G-D-D   D-A-D-D   D-G-D-D   D-A-D-D (2x)