What are some factors leading to anchor and anchor chain loss/damage?
The loss of an anchor or anchor chain is an event with costly and (sometimes) catastrophic consequences.
Under which circumstances is an anchor or anchor chain lost or damaged?
- When an anchored vessel is dragging due to strong current or heavy weather.
- When heaving up or dropping anchor in very deep waters.
- When dropping anchor without control by the windlass brake.
- When the speed of the vessel is high during heaving up or dropping the anchor.
- When the anchor is stuck or damaged due to rocky sea bottom.
- When the windlass clutch is disengaged during anchoring operation.
- During sailing, if the anchor is not properly secured.
- Breakdown of windlass hydraulic motor.
- Breakdown of the anchor stoppers.
Incident investigations have shown that the root cause of these damages if often the combination of the following technical and operational factors:
- Casting defects or unauthorized/improper repairs on the anchor shank or flukes.
- Excessive wear on the anchor D-shackle and/or D-shackle pin.
- Excessive wear of the anchor swivel.
- Mechanical damage of the anchor shank, flukes, swivel, D-shackle or anchor chain due to rocky bottom.
- Excessive wear / thickness reduction of the anchor chain links.
- Excessive wear on the mating surfaces of the windlass clutch that may lead to its accidental disengagement.
- Dislocated or missing anchor chain studs.
- Excessive wear of defects on the chain stoppers pins and hinges.
- Excessive wave loads on the anchor windlass due to anchor in very deep waters or heavy weather leading to breakdown of the windlass hydraulic motor.
- Excessive wear on the windlass brake bands.
- Contaminated hydraulic oil.
- Wrong setting of the pressure relief valves of the windlass hydraulic system.
- Improper selection of anchoring area (water depth, traffic, nature of sea bed). Particular attention is to be paid during deep water anchoring (Fujairah anchorage is a well known case).
- Improper monitoring of the weather forecast.
- Improper monitoring of the navigation equipment by the bridge watch. Late detection of vessel’s dragging leading to extreme tension of the anchor chain.
- Improper selection of anchor dropping method (by gravity or by windlass motor?)
- Improper communication between bridge and anchor watch on deck during heaving or lowering anchor
- Wrong setting of the windlass brake.
- Improper stowage and securing of the anchor during sailing.
It is important to understand the limitations in the design of anchor handling equipment.
IACS Rule environmental conditions (with wave loads included)
Current speed = 1.5m/s (3 knots)
Wind speed = 11m/s (BF6)
Significant wave height = 2m max.
Anchorage depth = up to 120m
The book “Anchoring Systems and Procedures” by OCIMF is a good reading.