Answer: The example of personification is in the sentence: He struggled up to the surface and tried to cry out, but the wash from the speeding yacht slapped him in the face and the salt water in his open mouth made him gag and strangle.
Explanation: The ability to slap someone in the face is a human characteristic.
Another possible example:
There was a chance that his cries could be heard by someone aboard the yacht, but that chance was slender and grew more slender as the yacht raced on.
Slender is an adjective usually used to describe a person's waist or arms. The word is also used to describe other things such as "a slender majority of voters" or "a slender chance of winning"