International Offshore Rule
Encyclopedia
The International Offshore Rule (IOR) was a measurement rule for racing sailboats. The IOR evolved from the Cruising Club of America
(CCA) rule for racer/cruisers and the Royal Ocean Racing Club
(RORC) rule.
shape with length, beam, freeboard
and girth measurements, foretriangle, mast
and boom
measurements, and stability with an inclination test. Additionally, the IOR identified features which were dangerous, or it couldn't fairly rate, and penalized or prohibited them. The measurements and penalties were used to compute the handicap number, called an IOR length, in feet. A typical IOR 40 footer (a one tonner) rated 30.55 feet.
The IOR rule encouraged wide short boats with limited natural stability. The crew weight was to provide the stability. This developed into the situation about 1977 when the boats winning in most IOR categories were dinghies with centreboards. The managers of the rule realised that this was not a suitable direction for seaworthy yachts and heavily penalised boats with rising keels.
The IOR is also used to define level classes, which instead of time correction, a boat in a given class-level has an IOR-length less than a specified value. The Ton Classes (Mini Ton, 1/4 Ton, 1/2 Ton, 3/4 Ton, 1 Ton, and Two Ton)–as well as 50-footer, ULDB 70, and Maxi
classes—are examples.
Often accused of prohibiting great boats by encouraging mediocrity, the IOR was run by the ITC, or International Technical Committee of the Offshore Racing Congress
, chaired between 1979 and 1987 by the late Gary Mull
of San Francisco. Early boats penned by Mr. Mull with material information regarding rule changes were Improbable, a custom Mull 40 and Munequita, a production Ranger 37. Very well sailed, both won their respective SORC classes in the early '70s and featured heavy amounts of tumblehome
and relatively low initial stability.
s which were built for line honours, not corrected time. This is in part why IOR handicap racing died off. The boats did not offer exciting performance off the wind, which was another reason for evolution away from the IOR.
Peculiarities of IOR designs result from features that increase actual performance more than they increase IOR length, or other odd rules; IOR hulls bulge at girth measurement points; a reverse transom moves a girth measurement point to a thicker part of the hull; waterline length is measured while floating upright, so large overhangs are used to increase waterline sailing at speed; the stability factor ignores crew, so IOR designers assume lots of live ballast; after the 1979 Fastnet race
excessive tenderness was penalized; full-length battens were prohibited to prevent mainsail
roach area, but short battens became strong enough that the IOR had to start measuring and penalizing extra mainsail girth; mainsail area adds less IOR length than jib
area, so new IOR boats are fractionally rigged; The IOR encourages high freeboard
and high booms and prohibits keels wider at the bottom than at the top (bulbs). The IOR, in sum, encouraged heavy boats that lacked fair lines and clean hull forms.
are simply limited to 30m (98'); encouraging improvements in boat design, and exciting sailing; not simply rule modification, as still plagues the America's Cup
competition.
The introduction of VPPs, or Velocity Prediction Programs
, morphed the science of yacht performance measurement. Inherent to the IOR was the concept of a measurement officer taking discrete hull measurements and the IOR formula assumed the hull lines behaved continuously between measurement points. The IMS took the actual hull lines and analysed their continuum, essentially eliminating funny bumps or hollows in the ensuing yachts and generally rendering much cleaner, faster lines that were far more exciting, safer to sail, and had higher resale value.
Cruising Club of America
-History:It was launched in the winter of 1921-1922 by a handful of experienced offshore sailors interested in cruising and the development of the cruising type of yacht....
(CCA) rule for racer/cruisers and the Royal Ocean Racing Club
Royal Ocean Racing Club
The Royal Ocean Racing Club also called RORC was established in 1925 as a result of a race to the Fastnet rock from Cowes and finishing in Plymouth. The RORC is the principal organiser of offshore yacht races in the UK, including the Fastnet race, the Admirals Cup and the Commodore's Cup...
(RORC) rule.
Rule context - past and present rating systems
The IOR was superseded (in the early 1990s) by the International Measurement System (IMS) and CHS. While some IOR yachts race at club level in more or less their original form, others had major surgery to make them competitive within the new rules.Rule components
The IOR concentrated on hullHull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
shape with length, beam, freeboard
Freeboard (nautical)
In sailing and boating, freeboardmeans the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship...
and girth measurements, foretriangle, mast
Mast (sailing)
The mast of a sailing vessel is a tall, vertical, or near vertical, spar, or arrangement of spars, which supports the sails. Large ships have several masts, with the size and configuration depending on the style of ship...
and boom
Boom (sailing)
In sailing, a boom is a spar , along the foot of a fore and aft rigged sail, that greatly improves control of the angle and shape of the sail. The primary action of the boom is to keep the foot of the sail flatter when the sail angle is away from the centerline of the boat. The boom also serves...
measurements, and stability with an inclination test. Additionally, the IOR identified features which were dangerous, or it couldn't fairly rate, and penalized or prohibited them. The measurements and penalties were used to compute the handicap number, called an IOR length, in feet. A typical IOR 40 footer (a one tonner) rated 30.55 feet.
The IOR rule encouraged wide short boats with limited natural stability. The crew weight was to provide the stability. This developed into the situation about 1977 when the boats winning in most IOR categories were dinghies with centreboards. The managers of the rule realised that this was not a suitable direction for seaworthy yachts and heavily penalised boats with rising keels.
Practical implications for sailors and owners
In a handicapped race, the IOR length was used to compute a time allowance, in seconds per nautical mile (s/M) which was multiplied by the distance of the race, and subtracted from the boat's actual time, to compute the boat's corrected time. Longer IOR length gave a smaller time allowance.The IOR is also used to define level classes, which instead of time correction, a boat in a given class-level has an IOR-length less than a specified value. The Ton Classes (Mini Ton, 1/4 Ton, 1/2 Ton, 3/4 Ton, 1 Ton, and Two Ton)–as well as 50-footer, ULDB 70, and Maxi
Maxi yacht
A maxi yacht usually refers to a racing sailboat of at least in length. It is also a Swedish brand of smaller sailing yachts.-Origin:The term maxi originated with the International Offshore Rule rating system, which in the 1970s and 1980s measured offshore racing yachts and applied a...
classes—are examples.
Often accused of prohibiting great boats by encouraging mediocrity, the IOR was run by the ITC, or International Technical Committee of the Offshore Racing Congress
Offshore Racing Congress
The Offshore Racing Congress is an international body for the sport of competitive sailing and is responsible for the establishment and maintenance of rating and classification standards used to define offshore, that is marine as opposed to inland, yacht racing handicap categories.-Ratings and...
, chaired between 1979 and 1987 by the late Gary Mull
Gary Mull
Gary Mull He was a successful yacht designer behind these popular Fibre-reinforced plastic boats.- Early life and Education :...
of San Francisco. Early boats penned by Mr. Mull with material information regarding rule changes were Improbable, a custom Mull 40 and Munequita, a production Ranger 37. Very well sailed, both won their respective SORC classes in the early '70s and featured heavy amounts of tumblehome
Tumblehome
In ship designing, the tumblehome is the narrowing of a ship's hull with greater distance above the water-line. Expressed more technically, it is present when the beam at the uppermost deck is less than the maximum beam of the vessel....
and relatively low initial stability.
Age, compensation and competitiveness
To account for improvements in design and materials, boats are given an old age allowance, which decreases their IOR length as time passes. In spite of the old-age allowance, about 3/4 s/M/year on a 40 footer, boats over 2 years old were usually not competitive, and was of little value to the Maxi yachtMaxi yacht
A maxi yacht usually refers to a racing sailboat of at least in length. It is also a Swedish brand of smaller sailing yachts.-Origin:The term maxi originated with the International Offshore Rule rating system, which in the 1970s and 1980s measured offshore racing yachts and applied a...
s which were built for line honours, not corrected time. This is in part why IOR handicap racing died off. The boats did not offer exciting performance off the wind, which was another reason for evolution away from the IOR.
Peculiarities of IOR designs result from features that increase actual performance more than they increase IOR length, or other odd rules; IOR hulls bulge at girth measurement points; a reverse transom moves a girth measurement point to a thicker part of the hull; waterline length is measured while floating upright, so large overhangs are used to increase waterline sailing at speed; the stability factor ignores crew, so IOR designers assume lots of live ballast; after the 1979 Fastnet race
1979 Fastnet race
The 1979 Fastnet race was the twenty-eighth Fastnet race, a yachting race competition held since 1925, generally every two years. In 1979, it was the climax of the five-race Admiral's Cup competition, as it had been since 1957....
excessive tenderness was penalized; full-length battens were prohibited to prevent mainsail
Mainsail
A mainsail is a sail located behind the main mast of a sailing vessel.On a square rigged vessel, it is the lowest and largest sail on the main mast....
roach area, but short battens became strong enough that the IOR had to start measuring and penalizing extra mainsail girth; mainsail area adds less IOR length than jib
Jib
A jib is a triangular staysail set ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast...
area, so new IOR boats are fractionally rigged; The IOR encourages high freeboard
Freeboard (nautical)
In sailing and boating, freeboardmeans the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship...
and high booms and prohibits keels wider at the bottom than at the top (bulbs). The IOR, in sum, encouraged heavy boats that lacked fair lines and clean hull forms.
Development, simplification and revitalised racing
Today, modern Maxis or "Super-Maxi's"Maxi yacht
A maxi yacht usually refers to a racing sailboat of at least in length. It is also a Swedish brand of smaller sailing yachts.-Origin:The term maxi originated with the International Offshore Rule rating system, which in the 1970s and 1980s measured offshore racing yachts and applied a...
are simply limited to 30m (98'); encouraging improvements in boat design, and exciting sailing; not simply rule modification, as still plagues the America's Cup
America's Cup
The America’s Cup is a trophy awarded to the winner of the America's Cup match races between two yachts. One yacht, known as the defender, represents the yacht club that currently holds the America's Cup and the second yacht, known as the challenger, represents the yacht club that is challenging...
competition.
The introduction of VPPs, or Velocity Prediction Programs
Velocity prediction program
A velocity prediction program is a program which solves for the performance of a sailing yacht in various wind conditions by balancing hull and sail forces...
, morphed the science of yacht performance measurement. Inherent to the IOR was the concept of a measurement officer taking discrete hull measurements and the IOR formula assumed the hull lines behaved continuously between measurement points. The IMS took the actual hull lines and analysed their continuum, essentially eliminating funny bumps or hollows in the ensuing yachts and generally rendering much cleaner, faster lines that were far more exciting, safer to sail, and had higher resale value.