202634 Twisted ship

A six-hold panamax bulk carrier had loaded a full cargo of iron ore, but crew were unable to close three ...

... of the forward hatch covers. Each hold had two hinged hatch-panels forward and two hinged panels aft. The hatch covers were of the standard McGregor type hydraulically operated sliding panels.

As the hatch covers were being closed the leading rollers tended to skew off the guiding trackway in the hatch coaming, unable to roll further. The hatchway was no longer a rectangle but had become a parallelogram, whereas the hatch panels remained undistorted.

It was suspected that the vessel had slightly ‘twisted’. This was established by taking freeboard measurements at various points on both sides of the vessel. The readings clearly confirmed the torsional twist of the vessel. Diagonal measurements of the hatch coamings also confirmed twisting of the vessel. The three aft holds were re-opened and an inspection of the cargo stow showed that iron ore in these three holds was slightly to starboard of centreline, whereas the cargo in the forward three holds was slightly to port of centreline.

Bulldozers were used to level the cargo in each hold and diagonal measurements were periodically taken to ascertain if levelling the cargo was having the desired results. Finally, the torsion of the vessel was corrected, and the hatch covers were successfully closed.

Lessons learned

• The vessel had broader than normal hatch squares, being a combination bulk/container type, thus more susceptible to torsional forces.
• Even a slightly uneven distribution of heavy cargo was sufficient to twist the vessel so that some hatches could not be closed.
• Manuals usually mention maximum trim and heel conditions but a note on the need for proper cargo trimming/ballasting the vessel to avoid coaming deflections during loading is equally useful.
• When making the loading/discharge plan, consider the potential need to close hatch covers at any time, for example if it rains. Continuous proper distribution of heavy cargo is a good practice to avoid nefarious twisting effects.