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    IRC Optimisation at a Glance.

    David Armitage, Head Sail Designer for Quantum Sail Design Group discusses several opportunities for optimising your sail plan.

    • Additional downwind sail area provides a good trade-off between rating and performance.

    • Square-top mainsails are the rage, and with good reason. However, be careful of too large a girth. Modest proportions seem better.

    • The luff perpendicular (aka LP, measured from the luff to the clew) seems to be penalized disproportionately. When determining the size of your largest headsail, consider where you’ll be sailing.

    • Reducing the headsail luff length can have a significant positive impact on rating. Losing the very top of a skinny triangle may not be much of a loss in terms of boatspeed, particularly on boats with non-overlapping headsails.

    Click Here is read the full article



    Improve your IRC Rating

    The following articles are reproduced with permission as appropriate, and copyright is as shown individually.

    Yachting World IRC articles by Matt Sheahan:

    Part 1 (published February 2010)

    Part 2 (published March 2010)

    Copyright Yachting World. No reproduction is permitted without express permission.


    IRC Challenge Race for Phuket King's Cup

    With IRC fleets growing in Asia, the 2010 Phuket King's Cup Regatta introduces the IRC Combined Fleet Race on Saturday 11th December - the final day of the Regatta. With start line off Kata Bay on Phuket Island's West Coast, this race allows cruisers and smaller racing yacht to take on the 'grand prix' racers on a level-playing field.

    'This is the first combined fleet race of its kind in Asia,' announced Simon James, Race Director.
    The number of IRC rated boats globally is approximately 7,500 in 40 different countries, 7% of which are in Asia and of those, 15% are in Thailand. Growing in global popularity, the IRC rating system is operated by Royal Ocean Racing Club (RORC), UK. The 2010 RORC IRC National Championship in the UK had 54 entries while in 2009 the Phuket King's Cup Regatta saw 87 IRC rated boats take part.
    'Each year the fleet of IRC rated boats grows. To my knowledge, the Phuket King's Cup Regatta attracts one of the largest IRC fleet in the world,' added James. 
    Since 2007, the Phuket King's Cup Regatta has seen a 65% increase in IRC rated boats, in part due to the growing number of IRC boats in the region. Japan, for example, has seen an increase of 133% 2007-2009, significant for the Phuket King's Cup Regatta as an independent survey by Infinity Communications & Consultant found that almost 10% of the 2009 Regatta fleet were Japanese.
    For the first time in Asia, the 2010 Phuket King's Cup Regatta will include one IRC Combined Fleet Race and one OMR Combined Fleet Race. Both will take place Saturday 11th December - the final day of the Regatta. Each class compete for a separate trophy and the bragging rights of being the 'IRC Winner' or 'OMR Winner'.
    The final day's race does not count to the overall Phuket King's Cup Regatta series which will be raced over four days instead of the traditional five days, this year.
    'The IRC Combined Fleet Race on the final day of the Regatta is a great idea which will give the cruisers and cruiser/racers a chance to have a go at the flat out racers. IRC is firmly aimed at all types, sizes and styles of boat and so this is an ideal use of the rule,' commented Mike Urwin, Technical Director RORC Racing Office.
    'While the spread of TCCs and range of boat types will inevitably mean that conditions on the day will potentially have a significant effect, I look forward with great interest to seeing the results.'
    Attending the 2010 Phuket King's Cup Regatta in official capacity are Jenny Howells Technical Manager RORC Rating Office, Emma Smith Ratings Secretary RORC Rating Office and Regatta Official Measurer Malcolm Runnells from Australia. 
    'We decided to shake things up a little on the final day this year, and think competitors will enjoy it. It'll be great to see all IRC's compete against each other and all OMR boats against each other. I'm sure we'll see some interesting results,' commented James.



    β€œAre we winning?

    “Are we winning?”

    You’re ahead, but is it enough? Mike Urwin explains how to calculate your position on the race course.

    Originally printed in 2005 IRC Yearbook

    Simplistically, each 0.001 of rating difference between two boats represents a corrected time difference of approximately 3.6 seconds per hour. This will however only be absolutely correct for boats rating very close to 1.000. So how can you be certain whether you are beating your rivals on the race course?

    Starting with boat A rating 1.010 and boat B rating 0.995, if Boat A sails for one hour, her corrected time will be 1.010 hours which is 1:00:36 (1 hour 0 minutes 36 seconds). Boat B will beat Boat A if her corrected time is less than that. To find out what this means in terms of time, we want to find Boat B’s maximum elapsed time. To do this divide Boat A’s corrected time by Boat B’s rating - 1:0:36 / 0.995 = 1:00:54. In other words Boat B can sail for up to an extra 54 seconds before her corrected time is more than boat A's. An easier way of doing the same thing is to divide the rating of boat A by the rating of boat B – ie 1.010/0.995 = 1.015 and 1.015 hours is 1:00:54.

    Notably, boats A and B have a rating difference of 0.015, thus confirming (54/15 = 3.6) the 3.6 seconds per 0.001 noted above. But if the boats are faster or slower, while the maths remains the same, the answer starts to vary from 3.6. If boat C rates 1.110 and boat D rates 1.095 (the same rating difference of 0.015 as A and B) the time difference for an hour’s racing is 1.110/1.095 = 1.0137 which is 1:00:49 – equivalent to 3.27 seconds for each 0.001.

    Similarly, boat E rates 0.910 and boat F rates 0.895 (again 0.015 less). The time difference for an hour’s racing by Boat E is 0.910/0.895 = 1.0168 which is 1:01:00 – equivalent to 4.0 seconds for each 0.001.

    For a given fleet of boats, this can then be dealt with by creating a table of time allowances for the fleet.

    The table above is the ideal way to deal with this. For occasions when you do not have this for whatever reason, another simple way of dealing with it is to divide 3.6 by your TCC. eg, 3.6/1.100 = 3.3 seconds or 3.6/0.900 = 4.0 seconds. The answer in each case will then be closer to the correct time allowance per 0.001 rating difference between your boat and a reasonably closely rated competitor. The answer will still be approximate, but rather better than just using 3.6!

    Mike Urwin


    HULL FACTOR; The IRC Thermometer!  

    IRC Hull Factor (HF) assessment is today to all intents and purposes wholly objective.

    The concept of HF first appeared in CHS, the Channel Handicap System, back in the 1980s. Initially, HF was wholly subjective. It was assessed by the two IRC rating offices using little more than intuition. With at that time CHS being largely an escape route from IOR for cruiser/racers and with only a small fleet centred largely in the UK and France, this worked perfectly satisfactorily. With the international growth of CHS through the 1990s, continued subjectivity plainly could not last.

    A significant part of the IRC Technical Committee’s work during this period was therefore aimed at developing ‘objective methods to answer a subjective question’. Thus, when at the end of the 1990s CHS became IRC, HF was already very largely objectively assessed. With continued work since then, HF assessment is today to all intents and purposes wholly objective.

    HF, perhaps because of its very nature, continues however to cause upset among owners and designers. The designers have a pretty good idea of what works under IRC in terms of the basic design parameters (length, weight, beam, draft, sail area, etc). But then along comes HF to upset all of that!

    Within the confidentiality constraints of a secret rule, plainly we cannot divulge the complete inner workings. We can however attempt to de-mystify and to explain the concepts.

    What is HF trying to achieve? It is addressing the otherwise unrated elements of a boat. It is making a judgement of the likely ‘efficiency’ of the boat on a scale between pure cruiser and pure racer. A thermometer perhaps!

    IRC philosophy is to permit cruisers to race against cruiser/racers against racers with all boats having a chance of success. This then of course does not prohibit the design, construction and racing of one- off ‘IRC designs’. It does mean that IRC must at the very least attempt to recognise these designs for what they are. And that is where HF comes in with the aim not of ‘killing’ the boat, but rather of identifying and quantifying that under the apparent finery of a cruiser hides a racer.

    How then does this happen? The starting point is the information contained on the IRC application form: Hull form, Keel Type and shape, Rudder, Hull material, Accommodation and Accommodation Materials, Other Appendage configuration. Expanding a little on these:

    We do not have the hull lines. We do know the general hull form, whether it is fair form, IOR inspired, clinker etc.

    We know quite a lot about the keel, particularly with in 2008 the publication of 13 generic keel types. We know whether it is just a fin or whether it is some form of low CG keel, whether or not it is a lifting keel, etc, etc.

    We know how many rudders the boat has and whether these are transom mounted, hung on a skeg or are spade configuration.

    We know what the boat is built from. Concrete through steel, aluminium, glassfibre, to the most exotic and up to date carbon and nomex.

    HF Le Theromometre de l’IRC Final MJU 080206 1 Mike Urwin & Jean Sans. February 2008We know how it is fitted out. Is it a completely stripped out dayboat or grand prix inshore racer? Or is it a fully fitted world girdling cruiser with running hot and cold everything. Or, as nearly always, something in between. And what materials have been used in the construction of the interior?

    We also know whether or not it has a novel appendage configuration. A canting keel or twin lifting daggerboards perhaps.

    And through the boat’s displacement/length ratio we have some idea of parametrically how heavy it is.

    And finally, we have any other information provided by the designer/builder/owner which may influence any of the above. The inclusion of some completely novel feature for instance.

    And how is this applied?

    We know that every aspect of a boat will have some affect on its speed. Weight carried as fitout is less ‘efficient’ in weight terms than the same weight as lead in the keel bulb. Concrete construction will result in a higher proportion of all up weight in the structure than steel than aluminium than glassfibre than carbon/nomex. A full fitout results in more weight distributed through the boat; higher pitching moment and in all probability a higher vertical centre of gravity. Etc etc. We can then assign a numerical value to each element using objective rules and methodologies developed over the years.

    Combining these then gives us HF

    That addresses new boats. When an existing boat is modified, a new keel or rudder perhaps, or changes to fitout (which must of course be declared), the same process is used.

    So, unlike the early days of CHS, HF assessment under IRC is as objective as it is realistically possible to be. Yes, of course there are subjective elements that we can never entirely escape. Is an extra berth worth as much as a microwave oven, a watermaker or a flat screen TV? But that is avoided by taking a global view of fitout rather than applying the principles of the contents of a trolley at the supermarket checkout! And anyway, the differences in the final assessed value of HF would be small, and even smaller in terms of TCC.

    And putting the whole thing into context, ultimately within the sensible range for a particular concept of boat, the effect of HF on TCC is small, generally less than 0.005. Certainly smaller than the apparent importance ascribed to it by many owners and designers. In reality, the effect is far less than the gains to be made from hull preparation, rig tune, sails, navigation, tactics, etc......

    Jean SANS and Mike Urwin February 2008