Suffice it to say that whoever's hand is on Granger's dick, he shall be permitted to proceed. Anchor away, matey.
Fitzwilliam is a possibility, I must admit. However, I am going to rule him out because his reaction would not have been to grab his captain's erection but to jump up on Granger's bed and sit himself down on that thing with all haste.
Jeffers wouldn't presume to enter his captain's cabin uninvited. So it's not he.
Humphreys adores the ground Granger walks on and, again, he would not presume, especially since Granger gave him the word a few chapters back.
Ta Da!!! It's Calvert! Yes, Granger's shower ploy on the deck worked to perfection. Calvert's not a happy camper, but he is a lustful camper. Is he really prepared to pout all the way to India and back? I think not. Calvert now understands he can't win this "exchange" - not that Granger is looking to win. He understands that Calvert was hurt by a cheating lover. But, practically speaking, dumping Sir Evelyn is not going to happen.
Yes, it's a mess. Thinking about it all too much will only drive you to distraction. Granger still has lots to sort out for himself as well. Meanwhile he has a job to do and needs to get on with it.
As you can plainly see, my analysis is irrefutable.