Final answer:
The boat owners need to start swimming towards the shore when faced with a sinking boat.
Step-by-step explanation:
In the given passage, the boat owners are faced with a life-threatening situation as their boat is at risk of sinking. Based on the context, it is implied that the boat owners need to start swimming towards the shore for their own safety.
Swimming is an important skill to have when engaging in water activities or in emergency situations like this. It is essential to know how to swim to ensure personal safety.
Therefore, the answer to the question is that after their thirties, boat owners need to start swimming towards the shore when faced with a sinking boat.