In 2005, the Storm Trysail Club, along with several other major yacht clubs, worked to implement the IRC handicap rule in the USA. IRC replaces IMS, which was rapidly waning. The IRC rule was chosen because of its great success in Europe and Asia. Within a year, over 500 certificates were issued in the U.S. and that�s expected to double in 2006. The following is an article, written by Greg Stewart of Nelson/Marek Yacht Design, about changes in the IRC rule for 2006 and how a boat owner can optimize his or her boat. This article first appeared on the US-IRC web site.
Greg, and everyone else in-the-know, says, the way to make sure you are getting the best possible rating is to bring your sails to your sailmaker to have them measured for IRC. Do not use the measurement certificate that was issued when your sail was new! All sails shrink over time.
IRC RULE CHANGES FOR 2006
Default Mainsail Cross-widths
Changes to rules 26.5.2, 26.5.3, and 26.5.4 amend the default value of Mainsail Upper Width (MUW) from 0.26*E to 0.22*E, and set the lower limit for rating credit to 0.20*E. This replaces the 2005 scheme in which IRC assessed the MUW as .26*E for mainsails even if the actual value was less. So for 2006, the ranges for mainsail cross-widths without rating penalties are now:
Width Default Values No Penalty Range
MUW .22*E .20*E to .22*E
MTW . 38*E .35*E to .38*E
MHW .65*E .61*E to .65*E
These defaults are similar to IMS and typical PHRF rating limits, and may limit the trend towards the extra-large upper roach mainsails within IRC.
Overhang Factor
A new rule, numbered Rule 23.2, Overhang Factor, has been added, which states: �Overhang Factor (OF) is an assessment by the Rating Authority of the bow and stern overhangs of the boat and their contribution to sailing length.� It appears that the method of determining the Overhang Factor from the measurements of overhang lengths and slopes is unchanged.
Hull Factor
Rule 27.2 is now titled Hull Factor (HF), and a new rule, numbered Rule 27.2.1, has been added, which states: �Hull Factor (HF) is an assessment by the Rating Authority of the features of the boat and their character and efficiency when compared to a basic cruising configuration.�
Note: It is not yet known whether there are any new practices that will affect how the Overhang and Hull Factor assignments are made, which in turn affect the IRC rating. Barring any significant change in approach, and based on the released information, it appears that the same attributes cited above will be favored by the IRC in 2006.
IMPROVING COMPETITIVENESS UNDER IRC
For existing yachts looking to improve their performance under IRC there are several means to consider, which include:
Record Accurate Sail Dimension
For yachts re-using their existing sails in 2006, it can be worthwhile to have the mainsail and large headsails re-measured to account for sail shrinkage. Also, the changes to the mainsail cross width measurements for 2006 may result in a rating reduction if the cross widths are within the no penalty range; if they are not, discuss with your sailmaker any reasons why they should not be.
Bow Down Measurement Trim Depending upon the hull form, a more bow-down measurement trim may be desirable to improve the yacht�s Overhang Factor assessment. Note that since IRC measurement is performed with the yacht in the empty condition, it may be necessary to relocate significant weight components (batteries, engine, rig, keel) to alter the trim, since no internal ballast should be onboard.
Install Heavier Keel
Since ample stability is encouraged, and internal ballast is harshly rated, the keel should include all of the ballast required. For many existing yachts, particularly those designed for IMS or IOR measurement handicap where stability was rated, quite a significant increase in stability and performance is possible with such a new keel, and often the impact on TCC is little or nothing. Prior to changing the keel or stability, a thorough engineering review, and possibly modifications, of the yacht�s supporting keel structure, chainplates and rig strength is required.
Change Rig Type
For yachts with multiple in-line spreaders and running backstays, a new rig with fewer swept-back spreaders and no runners may provide a significant reduction in TCC. This may also afford the opportunity to modernize the sail plan proportions and add larger masthead spinnakers. Prior to such a major rig change, a thorough engineering review, and possibly modifications, of the yacht�s supporting structure is required.
Note: The IRC allows up to six Trial Certificates each year to study the effect of an hypothesized change. Re-measurement is required before making most changes, and the local rating authority should be contacted for confirmation. Note also that IRC rule 2.5 states, �The spirit of IRC requires that owners and designers shall not seek means of artificially reducing the rating of a boat, e.g. increasing performance without a corresponding increase in rating.
Greg Stewart is a Naval Architect with Nelson/Marek Yacht Design, Inc. in San Diego, CA, who can be reached at [email protected].
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