A stability booklet, stability book, or trim and stability booklet is a document created by naval architects to help mariners calculate the vessels stability and attitude in varying conditions of load. The document is required of most larger ships by convention, being under the care of the master and always aboard the vessel. Stability booklets can range from 50-60 pages into the thousands of pages, depending primarily on the number of trim cases and load conditions evaluated.
A stability booklet is first and foremost a tool for the crew, used to ensure safe vessel operations. To this end, the data contained must be accurate and reliable. Assumptions must be stated, clear and logical. The organization must be consistent and conducive to use. Bulky booklets should be broken into individually bindered sections for ease of use. The booklet is also used to demonstrate compliance with stability requirements (see requirements, below). The stability booklet should contain enough information about the vessel (such as in the hydrostatics/cross-curves) to allow for future use - read in conjunction with the lines plan, the stability book may be used to create and calibrate a ships load computer or hull model (i.e., for a shipyard investigating modifications).
Not all vessels require stability booklets, however vessels of certain size, purpose or capacity are often required to have one prepared. The books must also pass approval of a number of bodies.
The stability booklets contents will vary between states, and may be more inclusive than described here. Individual stability booklets may not contain all parts, particularly if hand generated. Static characteristics (cross-curves, hydrostatics) may be required for a number of conditions of trim.
The introduction should include general information about the vessel. This could include:
- general arrangement.
- A description of the methodology used to generate the stability booklet (including how free surface effects were calculated, if tank contents were allowed to shift with trim/heel, how methodologies can be verified by hand, and what programs (if any) were used to evaluate the conditions).
- Description of the model or linesplan used: which appendages were included, the specific gravities of water used for generation of data, the extent of deckhouse or superstructure considered as effective, etc.
- Vessels principal particulars, IMO number, & callsign.
- Location, disposition, and quantity of permanent ballast.
- What regulations the vessel has been evaluated for (flag state, classification), the evaluation criteria of these regulations.
- Location and character of downflooding points - for example, if manual closures were considered as open or closed.
- a disclaimer (assuming good seamanship), including any restrictions or limitations on load, use, deck loadings, tank loadings, preferential fuel burning guidelines, etc.
- A definition of reference points and their location (particularly, the baseline used for draft marks fore/aft/midships); including sketches demonstrating the location and direction for all applied heel forces (tow heights, monitor heights, crane outreach & heights, etc.)
- A summary of the vessels required stability criteria in the various conditions.
- The supporting calculations for loadings, weather conditions, and heeling moments.
- The inclusion of the inclining experiment results, if applicable.
- The results of a lightship survey, if applicable, including the information of the sister ship and it's inclining experiment on which the weight characteristics are derived; where inclined, a copy of the vessels inclining test and approval letter.
- As desired, performance characteristics from sea trials.
Conditions of Load
For the vessels permissible draft range (ranging from light ship to the load line or scantling draught, whichever is greater), the following should be provided;
- Instructions on using the information within the book
- Worked example for a condition of loading
- Worksheets for calculating a condition
The following may be included within the stability book, or as additional documentation: