What is the maximum diameter for main propulsion shafts?

What is the maximum diameter for main propulsion shafts?

• A. 24 in
• B. 30 in
• C. 36 in
• D. 40 in

Answer: (B)

The size of a main propulsion shaft is limited by the space and support available in the stern tube and bearings, plus the need to fit cleanly through the hull and align with the driving gear. In typical Navy propulsion arrangements, the stern tube, bearing housing, and surrounding structure are designed to accommodate up to about 30 inches in shaft diameter. This provides enough torsional stiffness and bearing support to handle the engine or turbine torque, while keeping the hull penetration and supporting components practical in size and weight. Sizes larger than this would require a much bigger stern tube, heavier and more complex bearing systems, and more structural changes, which aren’t standard for most ships. Smaller diameters like 24 inches are used on smaller installations, but 30 inches represents the practical maximum for standard main propulsion shafts.

The size of a main propulsion shaft is limited by the space and support available in the stern tube and bearings, plus the need to fit cleanly through the hull and align with the driving gear. In typical Navy propulsion arrangements, the stern tube, bearing housing, and surrounding structure are designed to accommodate up to about 30 inches in shaft diameter. This provides enough torsional stiffness and bearing support to handle the engine or turbine torque, while keeping the hull penetration and supporting components practical in size and weight. Sizes larger than this would require a much bigger stern tube, heavier and more complex bearing systems, and more structural changes, which aren’t standard for most ships. Smaller diameters like 24 inches are used on smaller installations, but 30 inches represents the practical maximum for standard main propulsion shafts.