Rio cycle
Paul Hobson: ‘This is probably the cycle where I have seen the most equipment devel- opment. We have seen new boats, masts and sails and have had increased custom requests as the sailors look for that little edge.’ Hobson is most interested in the Finns since they allow more experimentation. ‘Because you can develop equipment the Finn is a unique class in the Olympics; they can also measure in two sails at the Games. ‘As we expected, the specific wind range (7-12kt) we were looking at for Rio meant sails that generate power while being flex - ible and forgiving. To save as much weight aloft as possible, for some years now we have also been using carbon headboards and battens, Cuben Fiber patches and for some sails even Cuben batten pockets. ‘While all Finn sails are obviously built to maximum dimensions, there are no restrictions on shape, meaning that we custom-fit each sail to the sailor’s specific mast(s) plus his height and weight. In today’s Finn fleet there’s also a wider weight range than before, with successful sailors now ranging from 88 to 104kg. The Finns also allow development in sail material, so Hobson says North devel- oped its own cloth during this cycle (the Xi Range) which has now become standard for their medium/heavy air sails. Mean- while, for their light/medium air sails the company uses a well-proven cross-cut laminate from Contender (Maxx). For the 470 class Nobu says that there continues to be a steady stream of customi- sation requests even within the tighter constraints of the class rules.
‘Our 470 mould shape requests have mostly come from the customers,’ he says. ‘What they require depends on the modes they want to perform. With our analysis and development tools we feel confident we can give them what they need.’
40 SEAHORSE
Specifics – 470 sail development North Sails Japan have pioneered their own methodology for 470 class sail development, using specialised tools and techniques more suited to this size of boat. The tools are more sophisticated than North’s generic software because the CFD and VPP elements have been calibrated and refined to be specific to planing dinghies, giving greater accuracy and therefore a shorter optimisation cycle. The use of telemetry in testing, photo
analysis using the Advanced Performance Analyzer (APA) tool and even real-time wind measurement at the 6m level relevant to a 470 rig have all contributed to this high level of accuracy.
‘Kinetic effects on small boats make conventional testing methods a real chal- lenge,’ says Nobu. ‘Therefore we had to develop a system to collect data from the test boats plus the relevant wind data from an instrument-equipped chase boat, then package this all together into a PC-based platform for analysis using the APA. This gives us a good handle on incremental gains and losses during testing sessions.’ Another important variable is the wind itself: given that the short height of the 470 mast sits within the boundary layer with most aero models, which assume a height of 10m, wind calibrations can be especially important in the modelling process. Images taken from the masthead in testing are fed into the APA to digitise sail shapes for comparison with other shapes in other conditions. CFD tools are then used to simulate test runs. As other para meters – such as live boat and rig geometries – are needed in this modelling, so mast and boat dimensions and stiff- nesses must also be rigorously measured. ‘The aerial images are great for record- ing a lot of information, and we record everything,’ said Nobu. ‘In the same photo we can see not only the sail, but also the
Above left: a 470 mainsail for Rio 2016 described using North’s Spiral design software and (centre) the 3D panel layout that will be used to achieve the shape derived from the Spiral output. The 3D layout produced by North’s Panel Design Programme then outputs the file for the laser cutters (left). Among its functions the 470 analysis package developed by Masanobu Katori allows live masthead sail imagery (above) to be displayed alongside numeric shape variations – all monitored in real time on the chase boat
mast, the rudder and the position of the crew. We see the range of headstay adjust- ment, spreader lengths and angles, mast base and shroud positions.
‘We use a laser measurement system we originally developed to measure mast stiffness – which can itself really vary a lot for a mast that weighs only 6-7kg.’ For sail development for Rio they needed to be ready for everything: sails that could twist off on the wavy offshore courses and sails that could be flat and sheeted in hard on the smooth waters of Guanabara Bay.
That said, while several different teams worked with North in preparation for Rio, Nobu says that due to the wide variability in expected conditions some crews eventu- ally opted for older, established designs because they knew them better and felt they could adapt them more reliably as conditions demanded.
‘We thought the venue would be mostly light winds, so our initial focus was in that direction,’ says Nobu. ‘But we realised after more research that anything could happen there, so then we needed to look at more adaptable shaping options.’
Another important aspect with the 470 upwind sail plan is matching mould shapes so main and jib work together efficiently. And this match can again vary by what the sailors want in their mode choices; for example, if a flat mainsail shape is desired, then the jib shape has to be tailored in harmony and not optimised independently as would be usual in bigger boats where multiple jib options are often available. Olympic sail design… a highly complex set of equations each involving the tiniest of detail variances.
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