In the same Master and Commander series, Dr. Maturin fell overboard and his timepiece got wet as well. One of the midshipmen retrieved some (they had a specific name for it) oil and displaced the sea water. This was the same oil.
In the books, Maturin was constantly falling overboard. He can do brain surgery with carpentry tools, but can't climb aboard a ship from a tender in the calmest weather without getting wet.