© Steb Fisher www.steb.com.au
SAILS AND YOUR IRC RATING
By Julian Plante - North Sails Australia
June 2007
While it is argued that the success of the IRC rule so far lies in the secret nature of the rule itself, optimizing the sail inventory to improve your boat’s rating becomes more of an exercise in rule of thumb developed from trial, error and experience. One new variable is the 2007 edition of the IRC rule, which until we start seeing some feedback from any rating changes on existing boats, or results from trial certificates, is somewhat of a grey area.
There are some simple ways you can optimize your sail inventory for IRC:
Re-measure Sails
Mylar sails will shrink with time and use, therefore re measuring your sails periodically, they will have usually reduced in area.
Increase Downwind Area
If you have a relatively small downwind sail plan, then increasing your sail area is a cheap performance gain compared to the rating penalty. For example, fractionally rigged boat with a hounds spinnaker hoist usually benefit from fitting a masthead hoist and spinnaker.
Another way to get more area is increasing spinnaker pole length (STL). A note of caution though, the biggest sail possible (and pole length) is not always the best and the best sail usually results from finding the right balance between size and efficiency.
Rate Slow Go Slow
If you cut down your sail area looking for a rating gain, then your boat will usually sail slower. There is a certain sail area for your boat that will make it perform well (efficiency) and this will generally produce a rating you can sail the boat to.
Bow Sprit vrs Conventional Spinnaker Pole
The move toward bow sprits has improved sail handling and made sailing more fun, all with the bonus if a rating gain for not carrying a spinnaker pole (or articulating sprit) which you can carry aft of the centerline. However there is a loss of performance for boats which do not generate enough apparent to bring their wind forward to a certain angle.
Boats which cannot achieve this apparent wind angle (generally small to mid-heavier displacement boats) will chase bigger spinnaker areas (SPA) to get depth down the course, but excessive area (and pole length) is penalized by the rule and is not efficient in terms of performance. Canting keel and lighter displacement yachts are examples of boats which are able to drag their apparent wind forward by sailing faster.
Big Roach Mains (and square tops)
As seen in the multihull fleets and America’s Cup, big square top mains create extra sail area and more efficient shape. However, they have highly developed rigs to support the extra loads and backstay systems which will not foul the head of the sail. The big top mains are measured now by the addition of a top girth measurement (MGT). However, it seems that rating penalty is balanced by the performance gains for some boats.
Headsails
Recent rule changes have limited the head width on headsails, which has stamped out experimentation with fat heads. Shortening the luff length (LL) of your headsails lowers the half leech point and half width measurement, therefore only has the effect of reducing the sail area, which comes under the heading of rate slow, go slow.
It is important to remember that as a rating rule, as the rule director Mike Irwin commented “good sailing is not penalized,” and neither are items like new sails which will give you a performance gain without rating penalty. There are other ways you can spend time and money optimizing your boat, such as changing your keel, rigging and so on, but the rating benefits may be unclear.