USCG Exam PracticeMaintenance, machine tools, drawings, and tables
A water-lubricated rubber stern tube bearing must be rebushed when which condition exists?
- A. Total clearance equals 6.4 mm regardless of shaft diameter
- ✓ Any water groove is worn to half its original depthCorrect
- C. The bearing surface shows visible scoring
- D. Weardown reaches 1.6 mm less than the clearance for amidship machinery
Why B is correct
46 CFR §61.20-23(b) specifically states that water-lubricated rubber bearings must be rebushed when any water groove is half the original depth. The clearance limits in §61.20-23(a) apply to non-rubber water-lubricated bearings, and the 1.6 mm reduction applies to aft-machinery installations of non-rubber bearings.
Cited:46 CFR §61.20-23