I take the opportunity to fix the reasons for the decision, which u-boat hit which steamer.
U 46 and U 47 attacked at the same time from the same side; U-47 attacking from a position further northward (grid 03), U 46 from a position further southward (grid 63). Both U-boats stated their torpedoes running 1500 meters before the first detonation was heard. That makes probable that U-47 really hit "Wandby" in column 1. U-46 heard the detonation and claimed his first hit. U-46's second torpedo hit "Ruperra", steaming south of "Wandby" in column 6.
I think we should first collect all available data before making a re-assessment. Several ships had changed their positions within the convoy HX-79 to fill gaps and to facilitate the planned split into the sections A & B. WANDBY had been in station #16 but moved over to #26 and RUPERRA had been in station #66 but moved to #45.
So the ships were closer to each other than it would appear on the initial A1 form for this convoy. However, I'm aware that not all ships in the convoy followed the emergency turn carried out after the initial attack by U-38 & U-47. SHIRAK in station #36 (between WANDBY and RUPERRA) failed to make the turn and was subsequently torpedoed by U-47. I think the question which of the other two ships were hit by U-46 or U-47 could be answered when we find out if they remained with the main body of the convoy or not.
It appears that WANDBY remained with the main body as she remained afloat after being torpedoed at 2240 GMT and at daylight found herself close to the abandoned wrecks of CAPRELLA and SITALA, which had been torpedoed half an hour later. However, no details about the sinking of RUPERRA are known yet - the ship sank fast and none of her officers survived.