Thanks and no, its not irrelevant. Lets sort these vessels once and for all.. :-)

Conclusion in John Gibsons info is this:

GRASMERE > WASTWATER > TIERN

(Veritas 1955 has TIERN (LLRG) as ex-WASTWATER too)

I also see information I dont quite get there:
Was the vessel originally ordered by AS Odd / v. AS Thor Dahl, Sandefjord, Norway, then taken over by the Royal Navy before delivery, then sold or given back to AS Odd after the war? Or is this a mixup?
AS Odd / v. AS Thor Dahl did offcourse own TIERN from 1946 to 1958. TIERN was not a salvagetug as the text indicates, but a whaler catching for factories NORHVAL and later ROSS and THORSHAVET in the Antarctic. But this only concerns TIERNs life.

I think the important in this story is when The Royal Navy sold (or gave back?) the whalers after the war. I think this is where the identeties has been mixed up.

Can anyone shed some more light on this?
(and did The Royal Navy indeed buy them and then sell them postwar?)