USCG Exam PracticeTwin-screw vessel handling
Twin outboards mounted on a transom bracket and twin inboards both apply a turning moment to the hull when thrust is asymmetric. Which statement BEST explains why their maneuvering response differs at low speed?
- A. Both configurations apply the turning moment at the same location relative to the pivot point; the difference in response is due solely to propeller side force reaching the hull through the strut and stern tube on inboards.
- B. Twin outboards apply the turning moment at the pivot point itself, so they produce rotation with no advance, while twin inboards always produce some advance during a twist maneuver.
- C. Twin inboards apply the turning moment well aft of the pivot point, producing a greater turning moment per unit of thrust difference than twin outboards, which apply the moment closer to the pivot point.
- ✓ Twin outboards apply the turning moment well aft of the pivot point, producing a greater turning moment per unit of thrust difference than twin inboards, which apply the moment closer to the pivot point.Correct
Why D is correct
USCG Boat Crew Seamanship Manual §10-D states that twin outboards on a bracket apply the turning moment well aft of the hull's pivot point, while twin inboards apply most of it at the reduction gear or V-drive, much closer to the pivot point. A force applied farther from the pivot point produces a larger turning moment for the same thrust difference, so the two configurations respond differently.