Question

(a) As a second engineer, how often would you check holding-down bolts to ascertain that they are tight? What methods are used to check tightness?

(b) If, soon after joining a ship, you found a number of holding down bolts slack, and fretting to have oceurred in the areas of the slack bolts, describe how-you would handle the situation.

Answer 1

Part (a)

HOW OFTEN HOLDING-DOWN BOLTS ARE CHECKED AND METHODS USED

Holding-down bolts should be checked regularly, typically at each planned maintenance interval (e.g. every 3-6 months, or at each survey/ overhaul), and after any major work or a period of heavy running. The frequency depends on the maker's recommendation and the vessel's operating pattern.
Methods used to check tightness:
Torque check: Using a calibrated torque wrench, apply the specified torque to each nut and confirm it reaches the value without further movement (if the nut turns before reaching the torque, the bolt is slack).
Bolt stretch/ elongation check: Measure the bolt stretch (elongation) using a micrometer/ stretch gauge and compare with the specified value.
Hammer/ feel check: A light tap on the nut/ bolt head and feeling for movement/ ringing can indicate looseness (a rough check only).
Visual check: Look for fretting, movement marks, or corrosion around the bolt/ nut.

Part (b)

HANDLING SLACK HOLDING-DOWN BOLTS AND FRETTING ON JOINING A SHIP

Report and record: Inform the Chief Engineer immediately, log the finding, and photograph/ record the affected bolts and the fretting.
Investigate the cause: Determine why the bolts are slack - e.g. incorrect initial tightening, bolt stretch/ relaxation, foundation/ chock deterioration, engine vibration, or a previous repair. Check the chocks (epoxy/ metal) and the foundation for damage.
Assess the extent: Check all holding-down bolts (not just the slack ones) for tightness, and inspect the bedplate/ foundation for fretting, cracks, and movement.
Rectify:

Re-tighten the slack bolts to the correct torque/ stretch using the correct procedure, in the correct sequence.
If fretting has occurred, clean the fretted surfaces, and repair/ renew the chocks and foundation as necessary (e.g. re-chock with epoxy resin, or re-metal the chocks) to restore proper support.
Renew any damaged/ stretched bolts.

Prevent recurrence: Ensure correct tightening procedure and torque, use the correct locking, and schedule regular checks of the holding-down bolts. Investigate and correct any excessive engine vibration or misalignment that caused the bolts to work loose.
Record the action and monitor: Record the repair and re-check the bolts after a period of running to confirm they remain tight.

✓ Verified Model Answer (Text Solution)

HOW OFTEN HOLDING-DOWN BOLTS ARE CHECKED AND METHODS USED

HANDLING SLACK HOLDING-DOWN BOLTS AND FRETTING ON JOINING A SHIP