Capt. Jack Aubrey: This is the second time he's done this to me. There will not be a third.
Capt. Jack Aubrey: England is under threat of invasion, and though we be on the far side of the world, this ship is our home. This ship *is* England.
Capt. Jack Aubrey: To wives and sweethearts - may they never meet.
Dr. Stephen Maturin: Jack, I fear you have burdened me with a debt I can never fully repay.
Capt. Jack Aubrey: Nonsense! Name a shrub after me. Something prickly and hard to eradicate.
Dr. Stephen Maturin: A shrub? Nonsense! I shall name a new species of tortoise after you: Testudo Aubreii!
Chosen answer: They stop singing because they hear Hollom joining in. There are very strict ranks in the Navy, and Hollom singing with the lower crew dissipates these ranks, which is undesirable. That Hollom sings with the crew is frowned upon by the captain, as can be seen by his serious/agitated reaction after Stephen mentions that Hollom has such a clear voice.