irc YeArBooK 2010
Screening
ISAF Offshore Special Regulations note that: ISO 12217-2 is expected to
be capable of being used as a guide to general suitability for competition
table 2
in Special Regulations race categories. This comparison is also shown
iSo Design category A B c D
by Table 2 (right).
Minimum STIX or RORC STIX 32 23 14 5
It must be clearly noted that if categorisation of races is by definition of
Minimum AVS 130-0.002*m 130-0.005*m 90 75
the required ISO design category (A, B, C, or D), that boats must satisfy SR Category 1-2 3 4 N/A
both the STIX and AVS requirements for that design category.
Where ‘m’ is the boat’s Minimum Sailing Weight
Alternatively, Organising Authorities may instead specify the numerical
S minimum qualifying requirements for STIX and AVS.
cheme
irc Stability and Safety Screening indices –
SSSn and StiX
q: my boat has a ‘sistership’ which has a different keel. can i use the
common queStionS
same data or will i have to get my boat measured?
A: ‘Sisterships’ are boats that are to all intents and purposes identical. So
q: What is StiX?
model variants require individual assessment.
A: It is the Stability indeX derived by the International Standard for the
q: how do i know if my boat has been officially assessed or if the
stability and buoyancy of boats, ISO 12217-2. STIX is calculated from
required data is available
the physical characteristics of each boat and is a number generally in
A: The RORC Rating Office publishes a list of boats for which STIX and AVS
the range 5 to 50. In a similar manner to the SSSN system, a higher
data is available, either assessed by a Notified Body or as IRC STIX.
value suggests greater seaworthiness.
Please see this list on our website www.rorcrating.com.
q: how does StiX work?
q: What happens if some of the data is not available for my boat?
A: The International Standard defines four Design Categories for boats
A: If either of stability data or a hull file are not available, then neither STIX
broadly related to ocean, offshore, coastal and local sailing. These
nor Design Category can be calculated and your certificate will show
are analogous (but not directly related) to the ISAF Offshore Special
SSSN only.
Regulations Categories. Each design category has a minimum
qualifying STIX value and also a minimum qualifying AVS (see below)
q: there is a hull file available for my boat, but stability has not been
which is linked to the minimum sailing weight (m in kg) of the boat.
assessed. What do i do?
A: A boat’s stability may be assessed either theoretically by a naval arch-
itect in accordance with the ISO Standard, or directly measured by an
Design category A B c D
inclining test.
Wave height (metres) up to approx 7 4 2 0.5
q: What are the requirements for theoretical assessment?
significant significant significant maximum
A: ISO 12217-2, Annex C, para C.2.2 Vertical Centre of Gravity, requires
Typical Beaufort wind force up to 10 up to 8 up to 6 up to 4
that theoretical calculation of Vertical Centre of Gravity (VCG) shall
Calculation wind speed (m/s) 28 21 17 13
be based on the calculated mass and centres of gravity of individual
Minimum STIX Value 32 23 14 5
components, raised by the addition of 5% of (Fm + Tc), where Fm is
Minimum AVS (degrees) 130-0.002*m 130-0.005*m 90 75
freeboard amidships and Tc is draught of canoe body, in both cases in
minimum operating condition.




q: What is ‘AVS’?







"
!

q: if theoretical assessment is not possible, how do i get my boat
A: Angle of Vanishing Stability, also known as LPS, Limit of Positive
inclined and what does this cost?

Stability. It is the angle beyond which a boat becomes unstable and





 
    
A: The RORC Rating Office and other National Authorities have measurers
will capsize to an inverted position.
trained to carry out inclinings. A paper is available from our website (www.
q: how is StiX calculated?
rorcrating.com) detailing how the inclining is carried out and specifying
A: In a similar manner to the calculation of SSSN, STIX is the product of a
the required condition of the boat. The Rating Office charges £22/m







#

number of different safety/stability-related features. These are:
LOA for the inclining itself. The owner will then need to consult the boat’s
Length, Dynamic Stability, Inversion Recovery, Knockdown
designer or other qualified person to calculate the stability at the required
Recovery, Displacement/Length, Beam/Displacement, Wind
angles of heel and supply the other required data.

!








#


!



 



 

Moment, Downflooding, and Reserve Buoyancy.
q: Will the calculation of StiX and AVS involve any additional q: Will StiX and AVS be automatically calculated for my boat?






measurement? A: Yes, provided that the Rating Office holds all the necessary data and the
A: Since 1998, the European Union’s Recreational Craft Directive (RCD) owner has completed and returned the appropriate form available from
has required that all new boats (except pure racing boats) sold in the EU

www.rorcrating.com.
must have been assessed for STIX/AVS by a Notified Body – an officially
q: What happens if i modify my boat?
recognised assessment agency. Many boats pre-dating this have also
'
"






!



A: Modifications to sails will not generally require any additional re-
been assessed. These boats will not require any more measurement.
measurement for STIX/AVS. Modifications to rig and/or ballasting may
Other boats may require some measurement. However, any which




 
!





require that the boat’s stability is re-assessed. Modifications to the hull,
have had their stability assessed (either theoretically or by an inclining
keel or rudder may require a new hull file. Please contact the Rating
test) for any purpose or for which a sistership has been assessed
'*"!
$(!,$!, "&,%#


11+)/12-0.///


'"'"!
Office with specific detail.
and for which a hull file (a computerised lines plan) is available will be
assessed by the IRC Rating Authority on receipt of a request by the
q: how do i use the StiX number and the AVS value on my irc
owner accompanied by the required data. In this case, certificates will
certificate?
use the nomenclature IRC STIX to show that the calculation has been
A: Exactly as with SSSN, the Race Committee will set minimum qualifying
carried out by us rather than a Notified Body.
values for each parameter depending on the nature of the race.
58
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IRC2010 Screening STIX.indd 58 27/11/09 10:28:16 1257436877845_page1_Wave2PDFRoute.pdf 1 11/5/09 4:01:20 PM
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