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OPTIMISING SAIL INVENTORY FOR IRC RATING

By Julian Plante - North Sails Australia
April 2008


While the new 2008 IRC rule from the Royal Ocean Racing Club (RORC) rating office is currently in effect for the Northern Hemisphere, the 2008 rule will be introduced in Australia during the winter season on the 1st of June. A review of this latest edition reveals a few notable changes as far as sail inventory measurement and management is concerned.

One of the most significant changes is the addition of a Headsail top width measurement (HTW) and the way Headsail area (HSA) is calculated. Combined with the IRC notice issued in January 2008, the intention of these rule changes are to discourage the extensively distorted leeches with pushed out roach at the top batten, and pronounced discontinuous hollow at the mid girth with a small batten to satisfy the rule.

As a result of these changes, the significance of shortening the mid girth to reduce the calculated sail area, has been made less powerful. The intention is to create a leech profile that is more even, and a fair curve between any battens and the rest of the leech, which will help prolong the life of the sails and make them easier on the eye! Previously, sailmakers had been exploiting a loophole in the way leech hollow was measured. The Equipment rules of sailing stated that where a sail edge is hollow, and the measurement point falls in the hollow, then this should be bridged by a straight line (unless there was a batten), and the shortest distance from the measurement point to the straight line measured. By placing a batten at the measurement point, the sailmaker could put a significant hollow in the leech at the measurement point to reduce the girth length (Figure 1)
Sail Design© RORC IRC Notice 2008/2

In their IRC Notice 2008/2, the RORC referenced rule 2.5 which states “The spirit of IRC requires that owners and designers shall not seek means of artificially reducing the rating of a boat”, and advised that they would be directing measurers to record the depth of any artificial hollow at a measurement point, and report this to the rating authority to decide if rule 2.5 is applicable and a rating correction factor applied. This determination appears to be at the discretion of the measurer, and the result should be to sway sail design back toward producing a leech profile that optimises fit with the rig and boat, rather than measurement purpose. Time will tell of course.

Changes influencing rating through mainsail measurement have also been introduced to provide greater equity for boats with smaller roach mainsails. This mainly affects boats with little or no roach including Cruiser/Racers, or cruising boats with furling mainsails. To achieve this, the minimum values of Mainsail Upper, Top and Half widths used in the calculation of mainsail area (rule 26.5.4) have been reduced.

Other changes to the IRC rule include the banning of battens in spinnakers, introduced by the development of the “Spinoa”, which was an upwind code 0 with battens and 75% mid girth to rate as a spinnaker. A change to the IRC rule by the rating office last year effectively penalised these sails out of existence, and the RORC have taken further opportunity to ban battens with the new rule introduction.

Finally, new rule 26.6.2.2 has been introduced in regard to a yachts downwind inventory, and allows for an extra spinnaker above the amount shown on a yachts IRC certificate in Category 2 or above races. It is important to note, that for this rule to come into effect, such a prescription must be referenced in the Notice of Race, and so this needs to go on any pre-race checklist to assist decisions on sail inventory optimisation.

Each year, the same questions arise as owner’s debate ways to improve their boats rating. Just to recap, there are some simple rules of thumb to consider when optimising your sail inventory this year:<

  • Re-measure sails – Mylar sails will shrink with time and use, therefore by remeasuring your sails periodically, they will have usually reduced in area.
  • Downwind area – If you have a relatively small downwind sailplan, then increasing your sail area is a positive performance gain compared to the rating penalty.
  • Rate low go slow – Cutting sail area looking for a rating gain, could be a false economy. Generally you could expect your boat to sail slower, and perhaps slower than the rating benefit. Rather, it is important when optimising your rating to consider the type of sailing and conditions that you expect to generally encounter, and the sail area for your boat that will make it perform well (efficiency), and this will assist producing a rating you can sail the boat to.
  • Bow Sprit versus conventional Spinnaker Pole – Smaller and or heavier boats will be generally better off sticking with a conventional pole and spinnaker setup. Lighter and or larger boats are able to sail fast enough to drag their apparent wind forward sufficiently, to achieve acceptable true wind angle targets downwind.
  • Big roach mains (and square tops) – Square top mains create extra sail area and more efficient shape. However, they require rigs, battens and luff slide systems that are sufficient to support the extra loads generated, and backstay systems which will not foul the head of the sail.

Before making any decisions, do your research and check with the experts to ensure the best results possible.