USCG Exam PracticeBearings, lubrication, and care of machine parts
Under 46 CFR, when must the after stern tube bearing of a vessel with propelling machinery located amidship be rebushed if the shaft diameter is 254 mm (10 inches)?
- A. When weardown reaches 6.4 mm (0.25 in) clearance
- B. When weardown reaches 9.53 mm (0.375 in) clearance
- ✓ When weardown reaches 7.95 mm (0.3125 in) clearanceCorrect
- D. When any water groove is half the original depth
Why C is correct
46 CFR §61.20-23(a)(1) specifies that for shafts exceeding 229 mm (9 in) but not exceeding 305 mm (12 in) in diameter with machinery amidship, the after stern tube bearing must be rebushed at 7.95 mm (0.3125 in) clearance. A 254 mm shaft falls within that range. The 6.4 mm limit applies to shafts 229 mm or less, and 9.53 mm applies to shafts over 305 mm.
Cited:46 CFR §61.20-23