That's one of the mysteries, Mark. I don't think there are any positive sightings of him between the launch of Boat 13 and when Hemming spoke to him at Boat A. Possibly he was already at A, but he might have been in the vicinity of C and D...with no surviving witnesses who positively identified him there. I suspect he walked straight down the deck from aft at #13 and began work on A, but we don't know. He could have been detailed to some other work.
Be interesting to see if anyone has any light to shed on this.