Stability:
Errors in Calculations
The Club appreciates that the pressures placed on Masters when in port undergoing cargo operations means that time is often short. However such pressures do not diminish the Master’s responsibilities in ensuring the vessel is in a seaworthy condition at all times. This includes correctly assessing the vessel’s stability.
We have seen many instances whereby errors have been made in calculations and unfortunately they are always negative errors – vessels do not have related claims because of a positive stability condition.
If the calculations are being made by hand, then it is good practice to draw up a pro forma prior to the assessment being made. This will require fewer inputs to be made into the calculation at the time of execution and reduce the exposure to mistakes. A suggested format is contained in Appendix 1.
Computers
The Club recommends that all dry cargo vessels especially those carrying containers are
provided with a computer (loading instrument) and proprietary software specific to the vessel
for calculating transverse stability and if applicable, longitudinal strength. By using such
software (which is Class approved) the potential for arithmetical errors is reduced as
calculations are carried out automatically, data input is minimal and the results are obtained
almost instantly. If the loading condition is such that the minimum stability requirements are
not met, the areas of concern are highlighted to the user.
In the early days of PC use on board vessels, the computers for stability calculations were required to be “type approved”, however this is not always a requirement today and Members should clarify the position with their Classification Society. A dedicated computer should be used for stability purposes and no other software should be loaded so that there is no possibility of the stability program becoming corrupted.
The following page is a computer screen output from a stability software package developed and marketed by Shipboard Informatics Ltd. London, which is one of many software packages available.
The programs are relatively easy to use as they are tailored to meet each vessel’s configuration (e.g. weight and buoyancy configuration). The deadweight weight data for cargo and consumables is entered and the stability calculations are made immediately. If any of the minimum stability criteria is not met, the error is highlighted in red, bringing it to the attention of the user.
Such a program removes the majority of the possible errors that can occur when carrying out manual calculations. It permits more complex calculations to be carried out quickly which give the Master all the stability (and longitudinal strength) information required in order to ensure the vessel is in an acceptable condition for departure, arrival and during all stages of the voyage.
Stability Software Screen Display
In addition to the advantages already stated, because the programs are easy to use it enables the inevitable last minute changes to loading plans to be thoroughly investigated quickly.
The ease of use will also encourage more frequent investigations into the stability condition of the vessel.