A vessel with a single tailshaft and machinery located aft has a non-rubber, water-lubricated after stern tube bearing. The tailshaft diameter is 200 mm (7.87 in). At what maximum clearance must the bearing be rebushed?

Why A is correct

46 CFR §61.20-23(a)(1) sets the rebushing clearance for shafts 229 mm or less in diameter with machinery amidships at 6.4 mm (0.25 in). §61.20-23(a)(2) requires that where propelling machinery is located aft, the rebushing clearance is 1.6 mm (0.0625 in) less than the applicable amidships value, yielding 6.4 mm minus 1.6 mm = 4.8 mm (0.1875 in).