Pinning the tail on the rating donkey


The new Infiniti 52 DSS is a breathtaking-looking race yacht whose successful creation demanded nearly as much fresh and logical thinking by the IRC rule managers as from the team that created her. Designer Hugh Welbourn and IRC rating manager Dr Jason Smithwick tell a complex story


Any new design starts with the client’s brief, and in this case we were asked to look at a predominantly offshore-oriented raceboat that would be sailed with a small crew – so a natural development of our successful previous 46-footer Maverick. We would be able to take much of the logic from that design and then see how best to translate it into something around the TP52 size. IRC-optimised was the primary rating


requirement for Hull #1, but interest in the boat from other corners of the world


52 SEAHORSE


necessitated that ORC and ORR would also have to be considered, along with more local systems such as CSA for the Caribbean racing. Our approach was very much focused


on all-round performance within the light- est possible framework commensurate with the rating implications, and then to have enough stability and sail area to make the resultant hull work as intended. DSS was always going to be a major contributor to the stability issues on a light hull, but we would still need something more than that at times to substitute for the reduced crew numbers and less weight on the rail. On the 46 we had used a canting keel


and this worked well, but the added complications of a canting system plus a canard for side force didn’t really fit the framework of the relatively lighter config- uration at 52ft. All the major rating systems have their


own now well-identified – but different – sweet spots and straying too far from these will land you with a one-trick pony. Not much use for offshore racing when you really have to be a good all-round boat.


This then leads directly into being able


to adapt the configuration to suit the mission, and by adopting water ballast along with a fixed keel/DSS base-boat we then had the means to cover the range from sailing short-crewed offshore, for the Transpac say, or inshore-focused with the maximum allowable crew quotient. A second heavier bulb option completes


the picture and is the only physical change required to shift modes between the two most extreme cases to maximum competi- tive effect (see Figure A, overleaf). One interesting insight from our early


initial runs is the relatively low rating cost in IRC of using water ballast at this size. There are more rating variations avail-


able as well – water ballast is split into two tanks port and starboard, so a single tank- fill rating plus a few more crew from the base of nine might be an option, especially if more sail changes are likely to be neces- sary as in, say, Mediterranean racing. Comparative numbers for ORR and


ORC were run for us by Greg Stewart, at the Nelson-Marek office in San Diego, along with times and deltas for US west coast races such as the Transpac and Cabo St Lucas, against known quantities in the Pac52 and TP52 classes, as well as other boats for which sound data was available. The same analysis was then run for other major offshore races including the Sydney to Hobart, Fastnet and Caribbean 600. All of this data helped us to assemble a good picture of the boat as a whole; but


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