Lake Ontario Offshore RacingRacer InfoIntro to Stability Screening

Intro to Stability Screening

One of the primary areas of concern for the Lake Ontario Offshore Racing Group is racers safety. Beginning in 2012, improvement efforts in this respect were two-fold; we have standardized the published Minimum Equipment Requirements across all events and have introduced the racing community to Minimum Stability Requirements for monohull yachts.

During these introductory years, the Organizing Committee will review entries for all races, determine a yacht’s Stability Index value based on sistership data and communicate with the owners of yachts that appear to fall below internationally accepted stability requirements for offshore events. Individual yacht’s Stability Index certificate is not a requirement, although a minimum is now set in the Notices of Race; this less formal approach will help race organizers and boat owners assess a yacht’s ability to resist capsize while promoting overall safety for the events.

Whereas formal stability screening has been used in oceanic races for years, the screening used for freshwater offshore races has tended to be less rigorous.  A significant hurdle is the lack of Stability Index value for boats in the types and size range in our fleet; high performance rating systems such as IRC, ORR and ORC already assign a Stability Index on the boat’s rating certificate, while most other entries will be assigned a Stability, Safety and Screening Numeral (SSSN) calculated by an engineer.

Background Information

Sine 1998, yacht manufacturers cannot place boats on the market in the European Community without compliance with the Recreational Craft Directive. One of the elements of the RCD is stability and compliance with ISO standards is required; the level of compliance has to be printed on the hull plate in the form ISO or CE Category as per below. Additional information is available at the International Marine Certification Institute.

There are many types of races ranging from trans-oceanic races beyond the reach of any outside rescue facility to inshore races of short duration where rescue boats are available along the entire race course.

ISAF, the sailing sport authority, has divided offshore races into 7 categories; in the Offshore Special Regulations they strongly recommend that for Categories 0 through 4 races the race organizer should require compliance with a minimum stability/buoyancy index.

Crafted as a yacht manufacturing design tool, the International Standards Organization (ISO) created the ISO 12217-2 standard for sailboats longer than 6m, with design categories (A to D) for different types of sailing conditions as they relate to wind and waves. These are used as a general guide to suitability for meeting the OSR categories as per the following table:

Summary of Maximum Design Category Conditions under ISO 12217-2
ISO Category A B C
ISAF OSR Category 1 and 2 3 4
Significant wave height* 7 4 2
Wind in knots 55 40 27

* Height in metres. Some waves will be double this height.

Stability/Buoyancy Screening Systems

The preferred systems for stability/buoyancy screening are:


Any boat, no matter where she was built, sold in the European Economic Area (EEA) since June 15, 1998 is required to have undergone a certification process involving many ISO standards. The standard germane to this discussion is ISO 12217 Part 2. These boats will carry an ISO Category label.


Boats independently verified as meeting the minimum sailing weight, STability IndeX (STIX) and Angle of Vanishing Stability (AVS) under ISO 12217-2 and meeting the other standards are assigned an ISO category as summarized in the table below. A STIX value is typically obtained via the IRC Rating Office or a naval architect.

Since this is the most recent and arguably most sophisticated screening tool available to date it is the preferred method.


In addition to using hull shape to determine the yacht’s rating, the International Measurement System (IMS) based rules such as the Offshore Racing

Council Congress (ORC) and the Offshore Racing Rule (ORR) offices calculate a STaBility IndeX (STBIX) that appears on the yacht’s rating certificate.

Stability, Safety and Screening Numeral

The Stability, Safety and Screening Numeral (SSSN) is an older system developed by the RORC in the early eighties; the same input parameters as required for a PHRF certificate can be used to calculate a stability value, thus for almost any sailboat.

Unlike the STIX and STBIX values, SSSN estimates stability from rather basic parameters as compared to the more rigorous and detailed process used by the other systems. SSSN is not intended, nor should be used, for unconventional boats including those with moveable ballast, wings or excessive flare.

Corresponding ISO 12217-2 Minimum Values
ISAF OSR Category 0 1 2 3 4
ISO Category - A A B C
STIX - 32 32 23 14
AVS - 130-0.002m
but always ≥100°
but always ≥100°
but always ≥95°
STBIX 120 115 110 - -
SSSN - 35 28 15 10
Minimum Sailing Weight (m) - 3,000 kg 3,000 kg 1,500 kg -

OSR Category 4 values are recommendations.


The Lake Ontario Offshore Racing committee requires a minimum stability values associated with OSR Category 3 events for all overnight races (Lake Ontario 300 Challenge, Susan Hood Trophy Race and LOSHRS 100-mile race) and recommends a minimum stability values associated with OSR Category 4 events for all LOSHRS daytime races.

Required values will be in the following order of preference for OSR Category 3:
  • minimum ISO Category B
  • minimum sailing weight of 1500 kg
  • minimum IRC STIX of 23 and minimum AVS of 130-0.005m but always ≥95°
  • minimum ORC or ORR STBIX of 103
  • minimum SSSN of 15 except for boats with moveable ballast, wings or excessive flare.
Recommended values will be in the following order of preference for OSR Category 4:
  • minimum ISO Category C
  • no minimum sailing weight
  • minimum IRC STIX of 14 and minimum AVS of 90°
  • minimum SSSN of 10 except for boats with moveable ballast, wings or excessive flare.
  • these minimum are not mandatory for entry into LOOR OSR Cat 4 races but are recommendation based on international best practices.

Note: that compliance with any of the screening systems mentioned herein does not guarantee total safety or total freedom of risk from capsize or sinking.

With special thanks to Richard Hinterhoeller for his efforts at researching the various screening systems.

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