Final answer:
The references don't explicitly mention the first sign of a pilot's ill health, but hints of potential issues include a whispered doubt about the vessel's control and a pilot's surprise at a wave's interference, possibly suggesting reduced alertness or unwellness.
Step-by-step explanation:
The first sign that the pilot did not feel well isn't expressly detailed in the provided references. However, a clue suggesting a pilot's ill health could be inferred from the passage where someone whispers, "She'll not make it!" indicating a possibility of the pilot's incapability to control the vessel due to ill health.
Another hint might be taken from the scenario described where a pilot is surprised by the growling of water, a possible indication of his reduced alertness or deteriorating condition. Nonetheless, without a direct statement regarding the pilot's wellness, these instances might only suggest that there was a problem, but not necessarily with the pilot's health.