Articles Posted in Stability Reports

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Alaska-Iceberg1200x600-300x150Vessel stability refers to the ability of a vessel to return to its upright position after being heeled over by wind, waves, or other forces. If a vessel is not stable, it is susceptible to capsizing. Each vessel is unique and therefore needs its own stability report prepared by a qualified naval architect.

Vessel stability was in the news again after the National Transportation Safety Board released its findings regarding the sinking of F/V PACIFIC KNIGHT, the vessel that capsized in Bristol Bay on July 25th, 2018. There were several contributing factors, but they all led back to stability. An overloaded vessel and an inadequate assessment of the vessel’s stability was cited as the cause of this devastating accident that took the life of a 59-year-old fisherman.

Vessel stability is complex and must be calculated by a professional. It is recommended that new stability reports be completed every 10 years or after any and all changes to equipment or modifications are made to a vessel. Stability is not a constant condition; it undergoes continuous changes during each voyage and through the life of a vessel.

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Crab_fishing_boatThe overall safety of the commercial fishing industry is becoming safer every year. Those are the findings in a report issued by NIOSH in July of 2017. However, experts agree that an area that needs improvement concerns outdated stability reports. The US Coast Guard requires all fishing and crabbing vessels to carry a stability report which has been prepared by a Naval Architect. Problems arise when these reports are out of date.

According to A Best Practices Guide to Vessel Stability published by the US Coast Guard, vessel stability is defined as “the ability of a fishing vessel to return to its upright position after being heeled over by any combination of wind, waves, or forces from fishing operations.” If a vessel is “unstable”, it does not have sufficient ability to counter these external forces, therefore it is susceptible to capsizing.

The two variables in the stability equation are buoyancy and gravity. Buoyancy is the force acting to push the vessel up in the water, making the vessel float. In stability analysis, the total buoyancy forces are distributed over the part of the hull below the water, and the buoyancy of a vessel is a fixed variable as it is based on the architecture of the vessel. Gravity is the force acting to pull the vessel down in the water. The total weight of the vessel includes all gear, fuel, catch, ice, bait, etc. These weights are distributed throughout the hull, and mathematically combined into a single point called the center of gravity. Because weight is constantly being added and subtracted from a vessel, gravity is not a fixed variable; it is constantly in flux.