Damage to an anchor windlass hydraulic motor

Outline:

An unexpected windlass failure – things always go wrong at the most inconvenient time and place!

What the Reporter told us:

The vessel anchored off port at an open anchorage, with no navigational hazards in the vicinity, on 31 December. On 02 January, at about 02:00 hours, the weather started worsening with strong winds up to 30-35 knots, gusting to 40 knots, and heavy rain. The crew observed that the anchor chain started slipping continuously from the brake and through the chain stopper. The Master was called and the engine room was notified. At 02:30 hours the Master commenced heaving up the anchor. At about 02:40 hours, when the 4th chain shackle was on deck, the windlass control unit and hydraulic motor developed a leak. Simultaneously, the crew realised that the windlass motor had lost power and they could no longer heave up the anchor.

A spare motor was available onboard and the crew replaced the defective motor. The job was completed at 13.50 hours and the anchor was heaved up safely at 14.50 hours.

During the repairs, the Master used the engines and managed to maintain the vessel in a safe position.

From the investigation that was carried out, the following should be noted:

• The vessel was anchored in a water depth of 34 meters with 6 shackles in the water.
• The vessel was in normal ballast condition. The drafts were 6.0 m (F) and 8.0 m (A).
• The prevailing weather conditions during the incident were NW winds 30-35 knots with gusts up to 40 knots and the sea state was high, with swell up to 4 meters. The deterioration of the weather had been predicted and relevant weather forecasts, via NAVTEX and INM-C, were available onboard.
• The Officer of the Watch (OOW) did not alert the master promptly when the weather started deteriorating. However, no instructions had been given on this issue in the Night Order Book or anywhere else.
• The windlass and anchor motor were in good operational condition prior to the incident. However, the ability of the windlass and the anchoring system to withstand the excessive loads/stresses that are applied in heavy weather was not assessed properly.
• The anchor chain stopper and its securing pin were damaged, most probably due to the high forces applied, leaving a gap which enabled the anchor chain to slip.

CHIRP Comment

CHIRP and the UK’s Marine Accident Investigation Branch (MAIB) have several cases of dragging anchors, the latest for CHIRP was published in Maritime Feedback 45. MAIB report 28-2012 details an incident where windlass damage was the precursor to a series of incidents.

Mariners do not always appreciate the limitations of an anchor, even when they take into consideration the depth of water and amount of cable to be used.  If winds of Force 6 are expected, the generic advice is for ships to heave anchor and go to safe waters or out to sea. Wind, wave and current limitations for an anchor system are given in the DNV-GL article highlighted below. Procedures and training should cover an understanding of the environmental and operational limitations of the anchoring equipment. Proper maintenance following manufacturer’s recommendations is essential. It is important to note that the wind speed limit should be greatly reduced as the wave height increases, because the anchor design assumes that anchoring takes place in sheltered waters. In addition, the effect of windage is much greater on a ballasted vessel, particularly larger vessels.

DNV-GL, The Swedish Club and GARD have published some excellent advice.  Most anchor losses are avoidable. References within the DNV-GL article include an anchor loss video “Anchor loss prevention” which is well worth watching.

In addition, the Board highlighted the fact that there have been several cases of anchor windlass motor explosions, some causing serious injury. An article from the Maritime Accident Casebook further discusses these. Maritime Accident Casebook – exploding windlass refers.

The DNV-GL anchor loss article states that 34% of anchor losses are due to weather, 24% due to the winch or motor failures, and 21% due to operational procedures. The above links are well worth reviewing to ensure that you do not become another anchoring statistic.

All of the references mentioned above can be accessed from the publications page of the CHIRP MARITIME website https://chirpmaritime.org/publications

Report Ends