As you will see, 1943 listings for ships sunk off the west coast of Africa include:
43/01/08 Tanker/oiler ALBERT L ELLSWORTH (8,309t, 1937) Sunk by U-boat off W Africa. Date approximate
43/01/09 Tanker/oiler MINISTER WEDEL (R, 6,833t, 1930) Sunk by U-boat off W Africa
43/10/22 Tanker/oiler LITIOPA (R, 5,356, 1917) Sunk by U-boat off W Africa
43/10/22 Trawler ORFASY (545t, 14/7/42) Lost, probably by U-boat torpedo off W Africa
You will also notice these listings do not include the Roxburgh Castle. I am assuming that is because these are Royal Navy vessels and she was a merchant ship? Anyway, we'll hope this info is useful to you.