USCG Exam PracticeMaintenance, machine tools, drawings, and tables
For a vessel with propelling machinery located amidship, at what maximum clearance must the after stern tube bearing be rebushed when the shaft diameter is 254 mm (10 inches)?
- A. 6.4 mm (0.25 in)
- B. 9.53 mm (0.375 in)
- ✓ 7.95 mm (0.3125 in)Correct
- D. 1.6 mm (0.0625 in)
Why C is correct
46 CFR §61.20-23(a)(1) requires rebushing when clearance reaches 7.95 mm (0.3125 in) for shafts exceeding 229 mm (9 in) but not exceeding 305 mm (12 in) in diameter. A 254 mm shaft falls in that range. The 6.4 mm limit applies to shafts 229 mm or less, and 9.53 mm applies to shafts exceeding 305 mm.
Cited:46 CFR §61.20-23