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Old 10-16-2008
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Sailboat design acronyms. IOR, MORC

Easy answer is just to enlighten me on what these abbreviations mean. That would be great, but I'd also like to get a better understanding of some of the design criteria that are/were typical of their time. What's the differences between the major designs?
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Old 10-16-2008
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These acronyms are abreviations for various rating rules. Rating Rules are different than Handicapped rules in that the boat is measured to obtain its rating and so designers can try to beat the rule to gain an advantage, but in doing so they are typically distorting a design in a manner inconsistent with the best design practices which would be followed if there wasn't a rule they were trying to beat. The most common are:
CCA- Cruising Club of America
RORC- Royal Ocean Racing Club
MORC- Midget Ocean Racing Conference
IOR- International Offshore Rule (or Rating)
MHS- Measurement Handicap System (I've seen other names that I can't recall at the moment)
IMS- International Measurement System
IRC- International Racing (I'm not sure what the 'C' means)

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IRC: Technically, IRC does not officially stand for anything. Originally, “IR” was an abbreviation for International Rule. However, since the Rule at that stage was not recognized under International Rule (sailing), that name was not permitted. So RORC simply decided to keep the initials as the name, and even after IRC received International Rule recognition, the name remained simply IRC.

Link: IRC (Sailing - Wikipedia, the free encyclopedia)

IMC: International Measurement System - Wikipedia, the free encyclopedia

MHS: What Jeff said but relevant info: US SAILING Offshore

IOR: International Offshore Rule - Wikipedia, the free encyclopedia
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The C is for "club"
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Typeforms

Each rule ended up creating a typeform, which simply put means that while each rule was intended to fairly handicap all vessels, the designers ending up discovering traits that were favoured by that particular rule. Here is a summary of the type forms (in my opinion),

CCA - American based rule. Relatively narrow hulls (compared to today) and shallow (for the day) with fuller ends and fairly steep and wide counter. The Cal 40 is a good example of a CCA type design.

RORC - English based rule. Beamier hulls with a more wineglass section and narrower sterns than CCA. Think of earlier S&S type designs.

IOR - Developed as a melding of the CCA and RORC. Sail area measurements more closely followed the CCA while hull measurements were more adapted from the RORC. Early type forms were more S&S type, quickly followed in the early 70's by the Peterson/Holland concept of short pintail sterns. Deep forefoot and U-shaped bow sections. Of course the Peterson trapezoidal keel became a feature of mid 70's IOR boats. Just when everyone thought the IOR promoted heavy, overcanvassed, downwind rollers - along came the Kiwis in the mid-late 70's with their big butt lightweight fractionals, which changed the landscape. Turns out that IOR Mark II actually encouraged lightweight fractionals rather than heavy mastheads, so the IOR quickly moved to effectively ban those types. Later (80's) designs were more moderate. Lightish weight designs with widish sterns and fractional rigs (up to the size where it was feasible)

MORC - This rule was limited to boats 30 feet and under. Short overhangs, wide sterns, moderate displacement and masthead rigs. Think Santana 30/30 or Pinnacle 30 as MORC typeforms.

IMS - Lightish designs with wide butts, short overhangs, plumb bows, fractional rigs, blended in keel bulbs (apparently IMS favoured this style as opposed to the distinctly separate bulb you see on most modern sport boats)

Not sure about the more recent rules - gave up caring about measurement rules a while ago.
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