USCG Exam PracticeTwin-screw vessel handling
The largest contribution to propeller side force on a conventional shaft-driven propeller comes from which physical cause?
- ✓ The shaft angle giving the descending blade a higher effective pitch and greater thrust than the ascending bladeCorrect
- B. The discharge current acting on the rudder blade
- C. The propeller working in the frictional wake layer dragged by the hull
- D. The top blade entraining air or working in aerated water near the surface
Why A is correct
While frictional wake, rudder interaction, and blade aeration all contribute to side force, the source states that the largest contribution comes from the angle of the propeller shaft: the descending blade has the higher effective pitch and produces more thrust, making blade thrust unequal around the arc and pushing the stern to one side. (USCG Boat Crew Seamanship Manual §10-A)