Final answer:
The provided text does not specify the sound Pi associates with the first few hours on the lifeboat, but it mentions the ambient sounds of the sea, such as the surf and waves.
Step-by-step explanation:
The sound Pi associates with the first few hours on the lifeboat is not explicitly mentioned in the text provided. However, based on the provided passages, the first few hours on the lifeboat are filled with the sounds of the sea, such as the low thunder of the surf on the shore and the occasional subdued growl of a cresting wave. The excerpts do not include any particular reference to Pi or the specific sounds he associates with the lifeboat experience, thus this question cannot be answered definitively based on the information given.