Measuring problem follows ship grounding

The Port of Auckland is looking at ways to more accurately measure the height of the sea on the Manukau Bar after a ship grounded on it lastyear.

The 4500-tonne freighter Spirit of Enterprise lost its rudder when it struck the bar on August 16.

A Transport Accident Investigation Commission report said the ship would have eventually lost its rudder because its rudderstock was already weakened by a fracture.

However, it expressed concern over the standard of monitoring of sea conditions.

It said the bar was too far from South Head Signal Station for the signalman to accurately estimate the height of the sea and it was inaccurately estimated on that day.

Harbourmaster John Lee-Richards said a recommendation for a data-gathering buoy - called a wave-rider buoy - to be put on the bar was impracticable.

"The problem is the conditions out there are so violent that every three or four months you would be looking for the buoy because it would break loose and they are very expensive."

Instead tests were being done on another existing wave-rider buoy farther down the coast to see if the conditions it underwent were the same as those at the bar. If they were, data from that buoy could be used to estimate the height of the sea on the bar.

"We have to determine that yet."

Mr Lee-Richards said an interim measure put in place after the grounding allowing big ships to enter or leave the Manukau Harbour only during the hour before high tide had been superseded by new requirements.

Ships now had to have calculations done on the space under the keel before they could pass over the bar.

- NZPA