ORCV Safety - Cat1 and Cat2 Stability

Which way is up?


'Aspect Computing', © and with thanks to Richard Bennett, Sydney Hobart 1998

The following information has been designed to assist you with getting the correct information together regarding the stability of your boat.

The refinements to the Special Regulations that came into effect on July 1st 2009 had a major effect on the ORCV and the way that skippers must provide documentation demonstrating resistance to capsize for their yacht. We will be requiring all competitors to comply with the current 2017-2021 Special Regulations, they are determined by Australian Sailing.

The refinements require you to provide a declaration and proof of stability by one of the following methods for,

Category 1 Races:

  • ORCI Stability Index of 115 or greater, OR
  • ISO 12217-2 Design Category A STIX minimum of 35

Category 2 races:

  • ORCi stability index of 110 or greater, OR
  • ISO 12217-2 Design Category A STIX minimum of 32

Please note that for an ORCi certificate to be a valid proof of stability, it needs to meet the following requirements:
• The boat is still owned by the holder of the certificate
• The certificate has been issued in the last five years
• The boat has not been modified
• The current freeboard measurements have been confirmed as being consistent with the certificate.

If a boat has an old IMS certificate and the boat has not been modified, the ORCV may consider it in part towards satisfying the stability requirements on a case by case basis.

What do I need to do if my boat does not currently comply?
The first step is to find out if your boat has one of the following:
• ISO Category A statement from the designer or other appropriately qualified person (typically a naval architect) issued in accordance with ISO 12217-2. However for Cat 1 races, each individual boat needs to actually be inclined whether or not the designer has certified ISO Category A status for your boat.
• IRC SSS assessment shown on IRC certificate (this can be found on some IRC certificates, and added by way of an application) which is useful only for Cat 3 races and above
• ORCi certificate in your name that is less than five years old.

If you have one of the above and you are happy to declare that no changes have been made to your boat which will affect stability, then you will meet the new requirements.

NB: A GZ curve provided by the yacht designer is shown on an ORCi Stability & Hydrostatic Datasheet and is produced as part of the ISO 12217-2 calculations. By itself, for a Cat 1 race, a GZ curve does not meet the YA Special Regs for stability!!! In other words, for a Cat 1 race, the ORCV will not accept a GZ curve provided by a yacht designer on its own. Supporting documentation from an inclination test will need to be provided to demonstrate that the boat's resistance to capsize matches the designer’s data provided. For Cat 2 races, a GZ curve may be acceptable and the ORCV will review such boats on a case by case basis.

A good video showing an inclination test is available here.

Next steps (Should you not have one of the above):
1. Engage a suitably qualified Inclination tester and Measurer

2. Revalidate your boat's ORCi certificate, by contacting Australian Sailing on 02 8424 7400 to discuss the process required.

3. To have STIX information added to your IRC certificate, please visit the RORC Rating Office website at www.rorcrating.com, where a your boat’s designer is able to complete an application form to have the inclusion of designer calculated STIX, AVS, and Design Category, on a Boat’s IRC Certificate.

4. Send copies to the ORCV and/or upload into Topyacht

What will it cost me?

Inclination and freeboard measurements $300. Keep in mind that this is a measurer determined fee and it may change depending on how much time it takes the measurer.

Crane costs if weighing is required - note there are group weigh days organised by AS and/or clubs.

• Australia Sailing revalidation fee $450+gst

Visit the Australian Sailing website for further information on new and revalidated ORCi & IRC certificates.

Obtaining your boat's GZ Curve.
A GZ curve is calculated by the yacht designer or naval architect. It is easily done if you or the yachts designer has an electronic hull file. You will then need to provide an inclination and the boat's weight. If you have the lines plan of you yacht, some naval architects will convert these plans to a hull file. We cannot give you an accurate cost for this process as you will have to negotiate with the yachts designer or a naval architect. Please remember and as mentioned above, providing a GZ curve by itself will not meet the requirements of the Special Regs. It is one of several bits of information that are part of the calculations behind ISO and IRC category, and the ORCi/IMS data.


The GZ or stability curve is a graphic presentation of a boats static stability. As the boat heels, it develops a righting moment, which is the force created by the ballast and hull buoyancy that works to resist the heeling. The stability curve shows this righting arm (righting moment divided by displacement) as a function of heel angle. When the righting arm turns negative (at 123 degree for this diagram) the boat will no longer resist the heeling force and will capsize. An important measurement on the righting curve is the relative areas under the positive and negative parts of the curve. In this curve the positive is 3.96 times greater than the negative. That means it takes 3.96 times as much energy to turn the boat from upright to capsize as from capsize to upright.


How can the ORCV help you?

We can refer you to qualified measurers and any weighing days we know of. We are also happy to discuss the process. Please call Simon Dryden 0418 145 909, or email This email address is being protected from spambots. You need JavaScript enabled to view it. if you need any further information.

By Simon Dryden, Ray Shaw and John Curnow, with many thanks to Glen Stanaway and Susan Veal from Australian Sailing.


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