The Queen Mary has been moored at an Essex dock since it was bought at auction in 2011 by London-based businessman Ranjan Chowdhury.
However, maritime enthusiasts the Friends of the TS Queen Mary have been trying to return the steamer to Govan by raising around £750,000 for repairs.
Coltrane has since joined the group as patron and hopes to see one of the last remnants of Scotland's industrial heritage back in home waters.
Aidan O'Donnell, trustee for the Queen Mary group, said: "We are thrilled Robbie has agreed to be our patron and we hope he will help raise money, interest and awareness.
"But the problem will be persuading the owner of the Queen Mary to let her go."