The National Transportation Safety Board issued an investigation report on the capsizing of the fish tender ‘Pacific Knight’ while at anchor off Alaska in July 2018. The investigation identified several contributing factors to the capsizing, including poor stability assessment by the captain, vessel modifications, overloading and slack water in the tanks.
On July 25, 2018, about 0630 local time, the commercial fish tender Pacific Knight capsized while at anchor about 11 miles south of Dillingham, Alaska.
Two of the three crew members onboard were able to escape the vessel and were rescued by a nearby Good Samaritan fishing vessel. The third was unable to escape and drowned.
About 1,439 gallons of fuel and 300 gallons of hydraulic oil were found onboard,with an indeterminable quantity released in the water.
The Pacific Knight, valued at $1.55 million, was declared a constructive total loss.
Probable cause
NTSB determines that the probable cause of the capsizing of fish tender Pacific Knight was the captain’s inadequate assessment of the vessel’s stability and the risks related to vessel modifications, slack water in the tanks, and overloading of the vessel.
Analysis
Witnesses to the sinking of the Pacific Knight recalled the vessel capsized to port and sank rapidly, leaving only the starboard quarter out of the water.
The vessel had no reported problems, and the hull showed no post-salvage signs of leaks or damage. Thus, there is no evidence that any hull damage, machinery defects, or structural failures led to the capsizing and sinking of the Pacific Knight.
At the time of the accident, the Pacific Knight was likely overloaded. According to witness accounts, while at anchor prior to the accident, the Pacific Knight had a very small freeboard and a stern trim that submerged the vessel’s name on the transom.
Even for vessels whose overall centre of gravity remains constant, a vessel operated at a deeper draft (lower freeboard) typically has less stability than when operated at a lesser draft (higher freeboard) due to a reduction in righting energy.
It also tends to lower the range of a vessel’s stability as seawater can enter any openings and downflood into compartments at lower angles of heel.
Further, excessive stern trim also reduces righting energy and makes downflooding through aft openings occur earlier.
As such, with slack water in the main fish hold, an induced heeling moment on the vessel from an external force such as wind, waves (even small ones), wake from another vessel, vessel movement from the current while at anchor, or contact with the bottom would have likely induced a list.
The list would have caused water in the fish hold to flow to the low (port) side of the vessel, and this free-surface effect would have been detrimental to stability.
The cumulative effect of these factors likely resulted in a condition of neutral stability, with little reserve buoyancy or righting energy to resist capsize.
The last stability assessment of the Pacific Knight was conducted in 1996, about 22 years before the accident, and would not have included any modification done to the vessel since then.
The weight and placement of the two cranes that the captain added to contract for tendering a month before the sinking likely increased the vessel’s vertical centre of gravity (based on the position in which the cranes were found when salvaged).
Though not required for uninspected fishing vessels like the Pacific Knight, once the vessel was substantially modified by removing and adding equipment, a revised stability assessment should have been conducted to reflect the changes.
Had it been, the captain would have had the necessary information to safely load the vessel for specific operations.
Read the report in full: NTSB-Capsizing-of-Fish-Tender-Pacific-Knight
