It's all very well saying 'get an IRC rating' but then you are faced with an application form full of acronyms and jargon!   For those not familiar with IOR, IMS or later ORC rating certificates (and there we go again with the acronyms!) it can all look a bit daunting.   
There are of course the official IRC definitions which are part of the full rule text, and this is NOT intended to replace those, but it is a quick guide to what all the letters mean. Most measurements are taken in accordance with the 'ERS' defintions - the Equipment Rules of Sailing published by World Sailing (formerly ISAF).  

See also our simple sail measurement guide and measurement drawings.

IRC: (at present) does not stand for anything.. but watch this space!
RORC: Royal Ocean Racing Club - and Rating Office - joint owners of the IRC Rule
UNCL: Union Nationale pour la Course au Large - joint owners of the IRC Rule
TCC: Time corrector IRC
ISAF (International Sailing Federation) changed it's name in November 2015 to World Sailing.  Where this website still refers to ISAF please read as World Sailing.
LH: Hull Length (note that sales brochure Length Overall sometimes includes pulpit/bow roller, not included in LH)
LWP: Waterline length
BO: Bow overhang
SO: Stern overhang
y, h, x:  Additional measurements taken at the bow and stern
P: maximum hoist point of mainsail (on mast)
E: maximum outhaul point of the mainsail (on boom)
J: from the mast to the forestay attachment point
FL: Forestay length
STL: Spinnaker tack length
Mizzen rig:
PY: maximum hoist point of mainsail (on mizzen mast)
EY: maximum outhaul point of the mainsail (on mizzen boom) 
MUW: Mainsail upper (7/8) width (ie. taken 7/8 of the way up the leech)
MTW: Mainsail three quarter width (ie. taken 3/4 of the way up the leech)
MHW: Mainsail half width (ie. taken 1/2 way up the leech)
HLUmax: Maximum luff length on any headsail
HLU: Luff length of largest headsail
HLP: Luff perpendicular - from clew to luff
HHW: Headsail half width (ie. taken 1/2 way up the leech)
HTW: Headsail three quarter width (ie. taken 3/4 of the way up the leech)
HUW: Headsail 7/8 width (ie. taken 7/8 of the way up the leech)
HSA: Headsail area
SLU: Spinnaker luff length
SLE: Spinnaker leech length
SFL: Spinnaker foot length
SHW: Spinnaker half width (half luff to half leech)
SPA: Spinnaker area
Mizzen staysail:
LLY: Luff length
LPY: Luff perpendicular
Stability and safety 
STIX: Stability Index
AVS: Angle of Vanishing Stability
SSS: Safety & Stability System
Please let me know if I've missed anything! 



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Header images by:

John Crawley (CAN IRC)  
Jinno (c/o JPN IRC)
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