VESSEL STABILITY

VESSEL STABILITY

Firefighting water allowed to accumulate aboard a vessel eventually will affect the vessel’s buoyancy and stability. Therefore, firefighters must continuously monitor and evaluate this water accumulation. Although fire personnel may be familiar with the theoretical concepts of stability (i.e., righting arm, metacentric height, and stability curves), they generally do not have the technical background necessary to make judgments on how a particular vessel will react. The effects of water on stability must be considered on a vessel-specific basis. How water affects a particular vessel depends on many variables, including size; displacement and arrangement; initial designed stability; weight and location of cargo, fuel, and ballast; and height of superstructure.

The higher the amount of water allowed to accumulate above a vessel’s center of gravity, the more it will adversely influence its stability. Water allowed to flow from one side of a vessel to the other will increase list by shifting weight to the low side—the free-surface effect. It is difficult to accurately predict when these effects may cause a vessel to list to a point at which the application of water must be interrupted. A vessel will not list in equal increments over a period of time. For example, a large vessel may slowly develop a list of 10 degrees over the course of five hours of water application. It then may incline an additional five degrees in just one hour as fire spreads to the superstructure, causing water to accumulate in high levels of the ship. Fire officers are advised to take the following measures to minimize the effects of water on a vessel’s buoyancy and stability:

  • Assign a functional sector to continuously monitor the amount of water applied on the ship and assess its effect on buoyancy, stability, and strain on mooring lines. Begin monitoring early in the incident by recording baseline draft and inclination.
  • Use water sparingly. If it doesn’t turn to steam, it’s probably doing more harm than good.
  • Begin dewatering operations early. Start bilge suction, and arrange for pumps to remove water.
  • Get technical advice. Realize that the data and calculations necessary to determine stability are out of our league. Decisions that can impact a vessel’s stability should be made after consultation with its master, chief mate, and the U.S. Coast Guard.

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