200661 Heavy weather damage

02 Mar 2006 MARS

 

A large container ship was New York bound from Gibraltar straits in winter. The weather routeing service had recommended a rhumb line route south of the Azores in view of a storm predicted to develop off the Grand Banks. Some two days into the ocean crossing, the frontal depression had deepened into a severe storm. The passage plan was progressively amended in response to worsening route conditions advice from the weather routeing service, which forecast estimated worst swells of about six metres, and 'unavoidable rogue swells' of up to eight metres. During the following night, with the storm centre located about 800 miles to the north, the ship began to pitch heavily to intensifying swells coming from the starboard bow, while the wind blew at a steady force seven from almost right ahead. Speed was reduced in stages to about 12 knots, but this did not prevent the shipping of heavy seas and the odd slam under the bow. By daybreak, it was observed that although the sea conditions were only moderately rough, there was a very heavy WNW'ly swell running at an estimated 20 knots speed, and easily washing over the forecastle bulwark, which was estimated to be about eight metres above the sea. Bilge high level alarms activated in the forward fore peak void space and stores room and an investigation team entered this zone via the under deck passage.

Water ingress was noted through the chain locker access doors (not watertight on this ship) and via electrical cable penetrations on the forecastle deck. Some water was also seen entering the power distribution boxes via the insulation sheathing of the winch control cables. The spaces were wiped/mopped/blown dry and temporary drip buckets were rigged under ingress points. Speed and heading were adjusted further to keep the swell on either bow for best seakeeping, but green seas continued to come over the bow throughout the day.

The following morning, conditions had abated considerably and a team inspected the upper and forecastle decks. The following damage was observed:
  • Spurling pipe covers displaced and one lost overboard;
  • All electrical junction boxes water-logged due to improper sealing of covers and flanges;
  • Windlass control stand set back by water impact;
  • Anchor cable measuring device damaged;
  • Forward ends of seven deck containers on bay 01 port and starboard (P&S) outboard stacks set in due to impact of swell waves;
  • Low insulation on all motor windings forward.

Root causes/contributory factors

  1. Extreme swell height, coupled with low freeboard;
  2. Worst conditions encountered at night when magnitude of swell was not evident;
  3. High relative speed between ship and opposing swell;
  4. Poorly fitted lids on electrical junction boxes and loose conduit pipe flanges.

Other lessons

  1. Although the motion of the vessel was never unduly violent, vast quantities of green seas were shipped, especially during the night.
  2. Given the distance of nearly 200 metres from the bridge to the stem, and the high deck load of containers, proper judgment of the conditions on the forward deck from the bridge proved difficult.
  3. The wave break forward of bay 01 had sloping outboard edges, with the result that the outboard containers on deck were exposed to water shipped over the forecastle bulwark.
  4. In extreme cases, under similar head swells, the phenomenon of parametric rolling can occur, causing the ship to 'flop' to very large angles, whereby there is a very real possibility of containers being lost overside.
  5. At the first sign or suspicion of green seas coming over the bow, speed must be immediately reduced, preferably to less than 10 knots through the water, depending upon actual conditions.
 

 

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