Louay Habib interviews Mike Urwin, joint Chairman of the IRC Technical Committee, on some detail technical aspects of IRC.
LH: One objective of IRC is to provide a rating that will allow the existing fleet to be competitive while not being a disincentive to development - a delicate balancing act and one that is more important than ever in the current environment. Would you like to comment on the 2012 rating changes designed to change the balance between boats with non overlapping headsails and designs with overlapping headsails?
MU: Recent years have seen a steady trend towards new designs having non-overlapping headsails. This, and the trend among some boats originally designed with overlapping headsails to convert to a non-overlapping configuration, has prompted sail designers to develop improved designs for these sails in lighter airs. Allied with the fact that modern sailcloth is better able to deal with the higher loads in tall, high aspect ratio sails, this has changed the balance slightly in favour of the non overlappers.
The changes this year are twofold. We have firstly taken a fresh look at the efficiency of different styles of headsail going back to fundamental physics and recognising also the sail design and cloth improvements. As a result, we have made some detail changes in this area. Secondly, historically, IRC has taken no account of leech hollow meaning that any boat with a hollow leech headsail (sailmakers want to build hollow in to improve sail longevity and to minimise leech curl and ‘motoring’) was paying a small amount for area that they did not have. Reviewing this, we could see no reason not to properly account for leech hollow.
LH: There is always a question with new sails regarding size versus the rating and getting the balance right for a particular boat. What kind of help and information can be obtained from the rating office, e.g. Trial certificates.
MU: A trial certificate tells an owner/designer/sailmaker what the TCC would be for the proposed change. It is then up to the owner/designer/sailmaker to decide in the particular circumstances of that boat and the racing that she does whether the change is worthwhile. We do not and cannot give consultancy in this respect.
But (without giving away secrets!) the sort of questions that owners might perhaps be asking themselves are related to in what wind speed do we change down/reef? Is my crew generally underweight? Do we do lots of reaching? Do we race in predominantly light/heavy airs? Are we more competitve in light/heavy airs? Upwind? Downwind? What sort of courses do we do? All windward/leeward? Passage races? Etc, etc.
Answering those, and all the other issues, then helps in deciding how to configure the boat.
LH: How does IRC treat spinnaker pole length? And what about ‘prods’ shorter than STL?
MU: In the good old days, boats could have spinnaker poles to a maximum in length of J. 1mm longer incurred huge rating penalties. That has not been the case under IRC for as long as I can remember. Firstly, STL (Spinnaker Tack Length – the length of the longest pole or bowsprit or tack point on the deck) is linked to spinnaker area, not J. Secondly, if the pole is a little longer, or a little shorter, the TCC will be a little higher or lower. This then allows the owner/designer to vary (within reason....!) STL to suit the actual boat and her sail wardrobe rather than be constrained by the somewhat artificial J.
IRC does not care about boats with short (ie shorter than the spinnaker pole when measured from the mast face) prods. Provided that the boat is rated for a spinnaker pole, she can also have a centreline bowsprit no longer than the rated STL without rating increase. If the prod is longer, then its length from the face of the mast becomes STL.
LH: What, if any, special circumstances affect the rating of yachts set up for two-handed sailing? What if I race my boat two-handed and fully crewed, can I have two certs?
MU: IRC Rule 9.2.1 addresses short handed certificates. This is clear firstly that a shorthanded certificate is only valid for shorthanded races and secondly that only the data listed in that Rule can be varied from that on the normal (primary) certificate.
IRC TCC for shorthanded certificates is calculated in exactly the same way as for normal ceriticates. So, the only point of a shorthanded certificate is to allow a boat to hold two IRC certificates in different configurations, one for fully crewed racing and the other for short handed racing, avoiding the necessity (and cost) of continually amending and re-amending the certificate. The corollary to this is that a boat that is only ever raced short handed does not need to hold a shorthanded certificate.
LH: How is it possible for Hull Factor to change either during a year or from year to year?
MU: Except in the rare case of an error here, or clarification of detail by a boat, HF will only change during a year if the boat is modified. That may be any physical change: a new or modified keel, re-ballasting, a new/modified rudder, or removal/addition of fitout. This latter is addressed at http://www.ircrating.org/en/technical-a-certification/certificates-extra-info/99-removal-of-furniture.
The asessment of HF is continually reviewed to firstly improve our assessment methods and secondly to incorporate novel developments in the design and construction of boats. Any changes to our methods are incorporated at the beginning of the next certificate year. So, an HF change from one year to the next without any change to the boat is most likely to be due to a detail change or changes to the methodology that the rating offices use to assess HF.
LH: RORC races typically announce class splits well before the event, however some regattas do not, which means that competitors have little idea of which class they will be in and who they will be racing against. Does the rating office have any guidelines to remedy this or are there plans to address the problem at IRC events?
MU: No! This is a matter for event Organising Authorities, not us. Although we are always happy to advise Oas.
This is always difficult for events. For long standing regular events particularly those such as the RORC Series which runs over the course of the whole season, the pattern of entries will be well established allowing class breaks to be pre-determined. For events where the number and type of entries may well vary significantly from event to event, the organisers need to retain the flexibility to set class breaks based on actual entries. If the class breaks are set in stone months before an event, very uneven class numbers are often the inevitable result.
LH: What are the advantages of getting an endorsed IRC certificate?
MU: The disadvantage is that it will cost a little more in terms of both cost and effort. So, if you just want to get racing, don’t bother! Get the boat (and the crew.....!) up to speed first.
Once you are up to speed, having the boat weighed and measured for Endorsement is likely (but not guaranteed!) to result in a small decrease in TCC because of the rating office’s conservative approach to unproven data. As an example of this, for unweighed production boats, we will use the weighed weight of the lightest example of the design. The likelihood is that your boat will be a little heavier. A similar policy is used in respect of unmeasured rig data.
The intangible benefit of an Endorsed certificate is the knowledge among you and your competitors that your TCC is correct. So, when you win, you can hold your head up high at the prizegiving.
LH: How does IRC prevent a boat with a ‘cosmetic’ carbon fibre interior rating the same as a boat with an identical interior but one built for everyday use?
MU: We weren’t born yesterday! We have numerous photographs of boats showing vases of flowers, bottles of wine, napkins, etc, etc on the boat’s saloon table. Which is in fact the engine box…..!
IRC application forms include questions about a boat’s fitout and also the materials used. If we are in any doubt, we invariably ask for greater detail by way of drawings, or preferably photographs.
We then have a standard methodology to asses this aspect of the boat. Work on this during the last couple of years has further improved our ability to detect the purely ‘cosmetic’ and to be confident that we are getting this right.
LH: Thanks Mike. There are many more questions I could ask. But that’s enough for now.
Note: IRC is jointly owned by RORC and UNCL. Mike Urwin (RORC) and Jean Sans (UNCL) are joint Chairmen of the IRC Technical Committee.