DNV GL, Gard and The Swedish Club have observed a negative trend in loss of anchors and chains and associated costs. A study into the root causes has revealed that a majority of these losses could be avoided by increased awareness of the environmental limitations, more attention to some key technical issues and general good seamanship. This article was originally published by DNV GL and we have condensed it for a ‘speed read’.
In most cases the anchor and anchoring equipment are subjected to excessive environmental loads than what is actually prescribed by class societies unified interpretation.
So what are the maximum environmental loads:
- Current velocity: max. 2.5m/s
- Wind velocity: max. 25m/s.
- No waves (sheltered waters)
In most cases, the loss of anchor has occurred when the environmental loads states above has been exceeded and the vessel outside sheltered waters. An equivalent environmental envelope outside sheltered waters was found as given by:
- Current velocity: max. 1.5m/s
- Wind velocity: max. 11m/s
- Significant wave height: max. 2m
Best Anchoring Practices:
- On a good holding ground, the anchor chain and the fore-runner must remain horizontal on the seabed to exhibit necessary holding power
- The Scope Number = Water depth:Length of the chain (Class recommends 6 to 10 scopes)
Did you Know?
The anchor winch motor is typically designed to lift the anchor and three lengths of chain (82.5m).
Two Main Reasons for Most Anchor Losses:
- The D-shackle is the single technical component which has the highest failure rate causing anchor losses. Typically, the D-shackle bolt comes loose due to a detached securing pin. The conventional way of assembling the D-shackle is to lock the tapered pin in place by hammering in a lead pellet, a small but essential element in the anchoring equipment. This connection is not readily accessible for inspection. However, special attention should be paid to this detail whenever possible – when heaving the anchor or when the ship is in port – and, of course, when the ship is in dry-dock. Tight securing of the anchor in the hawse pipe during the voyage is recommended to avoid excessive vibrations, which again can cause the pin to come loose.
- Anchor Brake Bands: The windlass brake is essential to control the payout of the chain and many anchor losses, reported due to loss of brake power and uncontrolled release of the chain. Corrosion of the drum and wear of the brake band lining reduces the brake capacity and the main problem is that the brakes are not adjusted according to makers’ recommendations.
Further key issues related to technical failures causing loss of anchor are listed below:
- Check the anchor carefully when in dry-dock for wear and tear.
- Check the securing of the D-shackle pin as often as possible.
- Adjust the brake band when the lining is worn. Read the instructions.
- Replace the brake lining when required, without delay.
- Check the condition of all devices for holding the anchor tight in the hawse pipe.
- Do not buy second-hand anchors or chains without certificates.
- Watch out for fake certificates. The price may be an indication.
- Make sure that the deck officers know the maximum environmental envelope the equipment can hold and make sure this is reflected in the shipboard anchoring procedures.
- Properly implement routine inspections and maintenance of essential components of the anchoring equipment. Class should always be contacted when repairs are to be carried out on the anchor and chain.
- When ordering new ships, evaluate the possible need for increasing the anchoring equipment beyond minimum IACS class requirements especially if you will be anchoring in deep waters.
To share this knowledge with the maritime industry, DVN GL has developed an awareness video which can be viewed here
Source: DNV GL