Earlier articles about the International Offshore Rule ('IOR') have looked at some of the key components of measuring a yacht under the rule, and deriving a handicap with the aim of allowing different size yachts to compete against each other at any venue around the world (Part 1 is here). Level rating was the non-handicap form of racing under the IOR, where each boat was designed to the same handicap rating, or ‘Ton’ class.  |
| Part of the big 43-boat fleet that contested the 1976 One Ton Cup in Marseille, France (photo Bateaux magazine) |
Looking at the level rating classes first, the glamour fleet were the One Tonners, which had the ‘Coupe Internationale du Cercle de la Voile de Paris’, or the One Ton Cup, as their holy grail. The Cup was so named because it was presented in 1899 by the Cercle de la Voile de Paris ('CVP') for competition by boats with fixed keels, rated at one ton or less under the French tonnage rule of 1892. These small boats, approximately 5m on the waterline, raced in Cowes or on the Siene until 6-metre class yachts were used for the trophy following the advent of the IYRU International Rule. The impressive trophy was just under a metre high and was carved out of a 10kg block of solid silver by a Parisian goldsmith.  |
| The One Ton Cup |
The last One Ton Cup in 6-metres was held in 1962. In 1965 the CVP declared that it should be used for yachts racing boat for boat at a maximum specified RORC rating (22ft). The clubs at La Rochelle soon after gave the Half Ton Cup for boats with an 18ft rating, and the Quarter Ton Cup for boats with a 15ft rating. The additional international racing that occurred under this arrangement became a major influence on the whole process for a change towards an international rating rule. With the arrival of IOR, it was agreed to use the same level rating concept. Thus in 1971 the One Ton class was defined at 27.5ft IOR, Half Ton at 21.7ft, and Quarter Ton at 18ft. There was also a Two Ton class which was not well supported at a 33ft rating and was changed to 32ft in 1974 (and later to 34.5ft). In 1974 the US delegates to the ORC presented a Three-Quarter Ton Cup for racing at 24.5ft, and the Mini Ton class was introduced in 1978 for racing at 16.0ft. In 1983 the rating limit for One Tonners was raised to 30.5ft, after a drop in support for the One Ton Cup at the old limit, and giving the class a dual purpose as they would now meet the lower rating limit for the Admiral's Cup. |
| The popularity of the Half Ton Class was evident from this photograph of a start during the 1976 Half Ton Cup in Trieste (photo Bateaux magazine) |
These limits were further adjusted to two decimal figures as measurement techniques became more precise (e.g., the One Ton limit became 30.54ft). The 50-Foot Class, followed a similar model using a limit of 40ft (increased slightly to 40.54ft in 1991), but used individual and variable ratings within this limit for some regattas, and no ‘Ton’ classification was applied to this fleet.
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| The 50-Footers enjoyed close racing on a level-rating basis for many years (photo Guy Gurney) |
In the same vein, Maxi yachts were those that raced under the IOR's rating limit of 70.0ft (which was subsequently eased in the late 1980s), but given the sometimes large variance in actual ratings for these large yachts their racing was usually based on handicap results, although line honours remained a keen focus.
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| Part of the Maxi fleet competing in the 1988 Kenwood Cup in Hawaii, with Sorcery (70.82ft IOR) leading Il Moro di Venezia (70.05ft), Ondine VII (70.04ft) and Matador (69.99ft) |
Associated with the Quarter, Half and One Ton Cups were race-specific trophies. For the One Ton Cup, these included the Trophee de la Societe Nautique de Marseilles, for the winner of the short offshore race, and the White Horse Trophy, for the winner of the long offshore race. |
| One challenge in changing Pendragon from her original configuration as a Three-Quarter Tonner to a One Tonner in 1979 was meeting the increased accommodation requirements for One Tonners stipulated by the ORC 'Green Book' regulations (photo Paul Mello) |
Each level rating class was subject to specific ORC regulations that governed the world championships (the ‘Ton Cups’) for each of the level rating classes (the ‘Green Book’). This set out the rating limits for each class, the rules under which each championship would be raced (such as the length and type of courses to be raced) and the maximum number of entries for any given championship. The Green Book also specified certain design parameters not otherwise covered by the IOR rule itself, such as the minimum height and area of headroom, freshwater capacity, the minimum number of berths, and even the minimum thickness of squabs to be carried.
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| A closely packed fleet of One Tonners during the 1984 One Ton Cup, the first held under the new rating limit of 30.5ft |
Level-rating yachts were also campaigned in mixed fleet regattas (where they might further optimise performance and fall in or out of the class limit), which necessitated the use of handicapping and the application of time correction factors.
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| Close racing between a group of One Tonners during the 1987 Admiral's Cup (photo Bateaux magazine) |
A yacht’s IOR rating was a length measurement, expressed in feet. For a yacht designed with an eye to the rule, its rating might typically be around 8-10ft less than its LOA. In a handicapped race, the IOR rating was used to compute either a Time Correction Factor ('TCF') expressed as a decimal figure, and which for 'Time-on-Time' handicapping was computed against elapsed time to provide a corrected time; or as a Time-on-Distance allowance, expressed in seconds per nautical mile. Time-on-Time is similar to a general handicap or PHRF system. Time-on-Distance was used by multiplying the distance of the race by a time factor, and subtracting from the boat's actual time, to compute the boat's corrected time (the current IRC rule dispenses with the conversion between rating and handicap, by simply expressing a yacht’s rating by way of a TCF).
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| A crowded start line at the 1985 Admiral's Cup, with 57 yachts (representing 19 national teams) rating between 30 - 40ft IOR in a single fleet (photo Guy Gurney) |
This was a further complication in the level of acceptance achieved by the IOR, at least in mixed-fleet racing. This is because no matter how accurate the measurement system, if the time correction formula was seen to unduly favour one size of yacht over another, the system would lose support. |
| Startline action during the 1978 Quarter Ton Cup in 1978, held in Japan (photo Guy Gurney) |
Under IOR, and as with the former CCA and RORC, the USA continued to use Time-on-Distance while others used a single figure TCF, and this also resulted in different perceptions of the rule. A committee of ORC sat for several years attempting to reach a single compromise on time allowances, and duly dissolved itself without finding a solution. However, both approaches were based on the same principle, in that a higher rating gave a smaller time allowance, and vice versa. |
| The diminutive Farr-designed KevFlyer, rating just 20.0ft, racing in the 1980 Clipper Cup (photo Phil Uhl) |
The generally adopted formula for the TCF adopted by the RORC for IOR racing was, at least initially, a relatively simple calculation: TCF = (R1/2 + 2.6) / 10. For example, a One Tonner, with a rating of 27.5ft, had a TCF of 0.774, while a Half Tonner, with a rating of 21.7ft, had a TCF of 0.716. |
| International mixed fleet racing under IOR, with Half Tonners (eg Swuzzlebubble, KZ3494) racing alongside the Maxi Kialoa III (background) during the 1977 Southern Cross Cup (photo Phil Uhl) |
As with the IOR rule itself, the TCF formula underwent further evolution, with yacht clubs able to adjust the formula to suit their preferences. For example, in 1975 the RORC produced the following amendment: TCF = 0.2424(R)1/2/1 + 0.567(R)1/2. The only significance of this was to create a ‘hard point’ in the time correction factor graph at the place of a ‘base’ yacht of 29ft rating (TCF of 1.000). This formula withstood pressure for further change until the mid-1980s, where bigger yachts were given some easement following the dominance of One Tonners in the 1985 and 1987 editions of the Admiral’s Cup, but the swing of the pendulum lead to something of a rout by the fastest 50-footers in 1989. Such problems with finding the 'perfect' formula were, at least for the Admiral's Cup, subsequently avoided by changes to the regatta format from 1991 with boats racing in level rating divisions.  |
| Changes to the RORC's TCF in 1989 saw the ascendancy of the 50-footers in that year's Admiral's Cup, with Jamarella taking individual honours overall, followed by Will (second) and Stockbrokers Container in fourth (photo Peter Ludlow) |
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| The Farr-designed Shockwave on her way to winning the 1992 Two Ton Cup (held in conjunction with the 1992 Kenwood Cup in Hawaii) |
Part of the text used for this article is adapted from the book A Lighter Ton - The Champion NZ Yachts of the 1970s, 2012
