🔍 Key Concepts

• Water-lubricated stern tube stuffing box purpose and design • How packing around a shaft behaves when the shaft is turning • Why controlled leakage is sometimes necessary in rotating shaft seals

💭 Think About

• Think about what happens to the packing material when the propeller shaft spins at high speed and the packing is squeezed tightly against it. • Ask yourself: what problem would occur first if absolutely no water were allowed past the stuffing box while underway? • Consider which choice describes something that must be happening continuously any time the shaft is turning, not just in special situations like shallow water.

✅ Before You Answer

• Verify which choices describe a function that is continuous and necessary for normal operation, not just in unusual conditions. • Check which option is directly related to friction and heat at the packing/shaft interface. • Eliminate any options that mainly concern parts outside the stuffing box (such as distant bearings or struts).