Integrity of Nansen-class frigates questioned by Helge Ingstad investigation

In its investigation into the collision between Norwegian frigate Helge Ingstad and tanker Sola TS in November, the country’s Accident Investigation Board (AIBN) has raised questions about the watertight integrity of the Nansen-class frigates, bringing shipbuilder Navantia into the spotlight.

A preliminary report released on November 29th found that confusion on the bridge of Helge Ingstad during a 04:00 watch turnover was the proximate cause of the accident. However, the subsequent sinking of the ship was said to have been caused by progressive flooding overcoming the watertight integrity of the frigate.

The Accident Investigation Board Norway has issued an addendum to the preliminary report, warning that the issues that sunk Helge Ingstad could apply to other Navantia-built ships.

“The AIBN has found safety critical issues relating to the vessel’s watertight compartments. This must be assumed to also apply to the other four Nansen-class frigates. It cannot be excluded that the same applies to vessels of a similar design delivered by Navantia, or that the design concept continues to be used for similar vessel models. The AIBN assumes that its findings are not in conformity with the required damage stability standard for the Nansen-class frigates”, the investigation found.

Navantia has offered to work with Norway on the investigation in order to clarify the accident. It said that it would “analyze all the possibilities, considering that some of the mentioned possibilities … are concluded from a very preliminary investigation”, adding that Navantia had not received any official communication or consultation about possible causes.

The AIBN found that the initial assessment by the crew in the wake of the accident was that some crew quarters, the aft generator room and the ship’s stores room were flooded, but that the ship was stable and could survive if the situation remained relatively controlled. The crew then witnessed water quickly flooding into the gear room via the ship’s hollow propeller shaft, with flooding then creeping into the engine rooms through the bulkheads. The board’s initial assessment, based on crew interviews, was that the stuffing boxes did not work as intended. “This meant that the flooding became substantially more extensive than indicated by the original damage. Based on the flooding of the gear room, it was decided to prepare for evacuation.”

The AIBN advised the Norwegian military to assess its ships to address the safety concerns, and advised Navantia to “conduct investigations into the issues identified during this initial investigation and to ascertain whether this is also an issue relating to other vessels.”

The AIBN’s preliminary assessment was that the accident was not caused by any single act or event, but by a series of interacting complex factors and circumstances. The investigation team continued to seek to identify and understand these factors. So far, the AIBN said that it had not seen any indication of technical systems not working as intended up until the time of the collision.

Meanwhile, during the weekend of December 1st and 2nd, the Coastal Administration continued monitoring the Helge Ingstad with daily inspections of the oil spill equipment. Patrol boat Bergen and anti-pollution vessel Utvær were in the area and had collected about 50m3 of oil mixture by December 1st. In total, about 90m3 of diesel mixed with water had been recovered by the Utvær.