Dear Lunder,
That was most strange.
After Olaf's room, I found myself outside, went everywhere, Captain not in his room or anywhere else, so I saved the game and closed it, whilst I did a few other things. When I loaded it again,I was on the deck with the Captain all ready to fire the cannon. So game ended quite happily. Bug perhaps?
Anyway, thank you once again for your help. It has been very much appreciated.