🔍 Key Concepts

• Mechanical shaft seals vs stuffing box and packing on propulsion shafts • What maintenance is normally required on a shaft sleeve and packing-type seal • Whether one special feature alone or all listed features together is being asked about

💭 Think About

• Ask yourself: Which options describe realistic, documented advantages of mechanical seals compared to traditional packing on real ships? • Consider if any one of the choices (A, B, or C) sounds too broad or absolute to be true in all installations. • Think about how mechanical seals are actually serviced: Do you usually have to disturb the shaft to repair them, and do they typically run with or without constant manual attention?

✅ Before You Answer

• Verify which statements are actually specific to mechanical seals, not just something that could also apply to improved packing arrangements. • Check if a truly correct answer must match normal practice on most commercial vessels, not a rare or idealized case. • Confirm whether the question is asking for one key advantage or whether it is possible that all listed statements are correct.