USCG Exam PracticeBearings, lubrication, and care of machine parts
A water-lubricated stern tube bearing (not rubber) on a vessel with propelling machinery located amidship must be rebushed when the after stern tube bearing weardown reaches what clearance for a shaft of 250 mm (approximately 9.84 in) in diameter?
- 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) specifies that for shafts exceeding 229 mm (9 in) but not exceeding 305 mm (12 in) in diameter with propelling machinery amidship, the after stern tube bearing must be rebushed at 7.95 mm (0.3125 in) clearance. A 250 mm shaft falls within that range.
Cited:46 CFR §61.20-23(a)(1)