Vessel stability is a fundamental component of seaworthiness so it is in the interest of all owners/operators to learn about this topic and ensure that their vessel possesses a satisfactory level of stability in order to ensure its safety as well as that of the people on board.
A vessel’s stability is the measure of its ability to withstand high winds, waves and other forces resulting from its operations (lifting, trawling, towing, etc.) and resist capsizing by returning to an upright position after being heeled over. Naval architects can determine the stability of a vessel from the lines plan 1 and the results of an inclining experiment 2.
The righting arm curve - a graph showing the forces acting on a vessel at different heel angles
This is documented in a stability booklet which gives the master an idea of how the vessel will respond under various loading conditions. The bottom of this page contains resources for more information on understanding the basic concepts of a vessel stability to help in the understanding of stability information.
Have a stability assessment conducted on your vessel and take corrective action if needed. Assess your vessel’s stability periodically and have all significant modifications to your vessel verified by a naval architect to determine their effect on the stability of the vessel. Be particularly careful about any modification that may have an impact on the weight of the vessel or on the watertight integrity of the hull and the superstructure.
For smaller vessels and vessels operating in protected waters, simplified methods for assessing stability are available.
General precautions against capsizing
(from the IMO Code on Intact Stability)
“Compliance with the stability criteria does not ensure immunity against capsizing, regardless of the circumstances, or absolve the master from his responsibilities. Masters should therefore exercise prudence and good seamanship, having regard to the season of the year, weather forecasts and the navigational zone, and should take appropriate action as to speed and course warranted by the prevailing circumstances.”
The applicable standard for intact stability 3 depends on vessel size and type.
TP 7301 - Stability, Subdivision and Load Line Standards (1975) sets out the requirements for: fishing vessels, passenger vessels carrying more than 12 passengers, tow boats, cargo vessels, and offshore supply vessels.
Small Craft - Stability and buoyancy – assessment and categorization (ISO 12217-1) applies, with some exceptions, to small non-pleasure vessels 4 built on or after April 1, 2005.
- Guidelines for Using the ISO Small Craft Stability Standard ISO 12217-1
- Frequently Asked Questions about Using ISO 12217-1
Small non-pleasure vessels built before April 1, 2005 do not have to meet specific requirements; however, owners and operators are encouraged to verify that their vessels have adequate stability. Ship Safety Bulletin 07/2006 sets out options for verifying stability.
For some small vessels, the Transport Canada Guide to the Simplified Assessment of Intact Stability and Buoyancy of Small Non-pleasure Vessels is a valid option.
Damaged stability requirements increase a vessel’s ability to withstand flooding and remain stable in case the hull is damaged. There are currently two standards for damaged stability:
- TP 10405 - Ship Safety Passenger Ship Operations and Damaged Stability Standards (Convention Ships) (1993)
- TP 10943 - Passenger Vessel Operations and Damaged Stability Standards (Non-convention vessels) ( 2007)
As explained in Ship Safety Bulletin 10/2007, TP 10943 was revised October 1, 2007. The timetable for compliance with the revised requirements ranges from six months to eight years, depending on the size of the vessel, the area of operation and the current degree of compliance to the Standard. Newer existing vessels (those less than twenty years old) are allowed additional time to comply.
Owners must confirm the extent of their vessel's compliance with the revised Standard. In their own interests, this should be done sooner rather than later because, for some larger vessels, the schedule may call for implementing the provisions by April 1, 2008. The sooner the assessment is carried out, the more time the owner will have to determine what, if anything, should be done to meet the provisions. Transport Canada will not be assessing damaged stability for owners. Marine consultants who have stated they are available to assist with stability assessments
Anyone that will be carrying out an assessment should be advised that particular attention should be given to the accuracy of the lightship data (Part III of the Standard). Owners should also be advised that when reviewing the damaged stability of the vessel, the intact stability calculations should be updated for 75 kg per person (SSB 05/2007).
Fishing Vessels and Stability Booklets
A stability booklet is a tool used to determine the limits of a particular vessel’s stability.
A fishing vessel must have a stability booklet if it:
- is more than 150 gross tons; or
- carries capelin or herring in bulk; or
- has one or more factors that decrease stability identified in Ship Safety Bulletin 04/2006
Other Sources of Information…
To better understand stability and stability booklets, check out the following links:
- Fishing Vessel Stability Simulator
- Small Fishing Vessel Safety Manual - TP 10038
- A Best Practices Guide to Fishing Vessel Stability- United States Coast Guard
- Safe at Sea – Measuring Stability – a 15 minute video on the development of a stability booklet based on a real inclining experiment (available from FishSafeBC)
- Fishing Vessel Stability – Make it Your Business - the handbook for the FishSafeBC stability education program (available from FishSafeBC)
FishSafe BC is a British Columbia fishing industry driven program for improving safety on board commercial fishing vessels. The FishSafeBC Stability Education program is designed for fishers and their unique operating conditions. Courses are facilitated by fishers, who are able to communicate the material in a way that others can’t. Talk to your local association about organizing courses in your area.
1 [a depiction of the hull form]
2 [evaluation of the vessel’s floating condition and of the effect of weight movements on the heel angle in order to accurately determine the vessel displacement and centres of gravity]
3 [an undamaged vessel’s ability to right itself]
4 [vessels used for other than pleasure that are 15 gross tonnage or less (approximately 12 metres or less in length) and carry no more than 12 passengers]
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