ORCV Safety - Cat1 and Cat2 Stability


Which way is up?

ASPECT_RichardBennett

'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 changes 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, determined by Australian Sailing.

The regulations require you to provide a 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 (which requires a minimum STIX value of 32)

Please note that for an ORCi certificate to be a valid proof of stability, it generally 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 in any way that impacts stability (this may need to be verified by confirming the current freeboard measurements are 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. This should be sufficient for Cat2 races 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 most 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.

  • An old IMS certificate may be helpful and will be considered by the ORCV on a case by case basis.

  • Screening Value, a number derived in accordance with Appendix B, Section B5 of the Special Regulations but is only applicable to Cat3 races or above.

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 by submitting the ORCV Stability Declaration, 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, the ORCV will not accept a GZ curve provided by a yacht designer on its own. Supporting documentation or calculations, typically requiring an inclination test will need to be provided to demonstrate that the boat's resistance to capsize matches the designer’s data provided.

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 (the ORCV can provide the contact details of locally qualified people). In order to interpret the inclination test results you will need to know the exact underwater shape of the hull which is provided in an electronic hull profile. This is usually be available from the yacht designer and if necessary can be determined by a local measurer which will involve additional time and cost.

2. Revalidate your boat's ORCi certificate, by contacting Australian Sailing on 02 8424 7441 to discuss the process required.

3. To have STIX information added to your IRC certificate, please visit the RORC Rating Office website to see if your boat has an assigned STIX Rating that can be in turn added to your IRC certificate by contacting the IRC Rating Office. This alone is generally sufficient to meet the requirements of Cat2 racing.

4. Send copies to the ORCV and upload into Topyacht

What will it cost me?

Inclination and freeboard measurements typically a few hundred dollars. 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 which is a cost effective way to obtain your boat's weight.

• Australia Sailing revalidation fee of about $500 (contact Australian Sailing for the exact fee).

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

Stability Curve.

XLR8 stab

The GZ or stability curve is a graphic presentation of a boats static stability and is produced during ORCi or STIX analysis. 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.

 

ORCV_Icon ASPECT_RichardBennett

The GZ or stability curve is a graphic presentation of a boat’s static stability and is produced during the ORCi or STIX analysis. 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.