Poor welding has been blamed for a potentially dangerous incident last year when the rudder broke off a 1185-tonne cargo ship.
A Transport Accident Investigation Commission report outlines how the Auckland-registered Southern Tiare lost its rudder off the northern Hawkes Bay coast on June 4.
The ship was returning to
Napier from the Chatham Islands carrying livestock when it altered course to minimise the effects of rough seas.
The master was standing on the foredeck when he noticed the ship's head swinging back into the swell.
The second officer then told him that the steering had been switched from automatic to manual but was not responding.
The chief engineer reportedly heard a loud bang in the engine room and they eventually concluded that the ship had lost its rudder.
The bow thruster was used to keep the ship on a safe course.
Contact was made with the ship's base in New Zealand and a tug from Gisborne met the Southern Tiare at 2am the next morning and towed it to Napier. Investigations showed the rudder welds had been inspected a couple of years earlier and passed as safe.
But examination of the remains of the rudder assembly showed cracking to welds on the existing rudder assembly.
The report concluded the loss of the rudder itself was the result of poor weld fusion and penetration.
Water was likely to have entered the supposedly airtight gap between two sides of the rudder, adding weight to it and causing corrosion.
The bang heard by the ship's engineer was probably the sound of the rudder breaking off and hitting the hull.
There was no evidence it had struck a heavy object such as a rock, the report concluded.
The commission made safety recommendations to the International Association of Classification Societies urging vigilance when inspecting welds during construction.
The crew of the ship was considered to have taken appropriate action during and after the incident.
- NZPA
