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Design


With ongoing development, including a new rig and sails for the Jules Verne, the former Banque Populaire V is still getting faster. What is perhaps a little scary is that, according to co-designer Vincent Lauriot-Prévost, were the same team to repeat the project today there are far more substantial gains now on the table in terms of better foils and build materials…


As big as it gets (for now)


Denis Gléhen, head of design at Hervé Devaux’s engineering studio HDS, describes the creation of a new mast for Dona Bertarelli’s modest trimaran Spindrift 2


Today the development of large and aggressive multihull platforms, as seen in the last two America’s Cups, has been reined in a little with the move to a predominantly one-design Cup culture. But in France the creative spirit lives on, with a new generation of profes- sional skippers moving into classes like the Multi 100. Before all that, however, we were asked to put together an all-new, lighter spar for the recent Bertarelli/Guichard Jules Verne attempt with the former Banque Populaire V.


The Jules Verne Trophy was won in 2012 by LoÏck Peyron on the same VPLP-designed tri with a time of 45d 13h. But when Spindrift acquired Banque Populairein 2013, they were convinced that they could knock off more time, helped by substantial technical improvements (certain) and possible gains in the weather conditions encountered (maybe).


The objective for co-skippers Dona Bertarelli and Yann Guichard was to optimise the boat more globally, speeding her up in light air while preserving that astonishing heavy-air performance. As we began our analysis, it quickly became evident that taking BP’s performance up a notch would depend primarily on saving weight, in particular in the rig and sailplan.


The 2012 BP team recognised that they were only occasionally using the full height of the original 44.5m wing mast; hence weight could be saved with a smaller spar at little cost around the world. But simply shortening the existing rig was not good enough. To reduce aero drag and make use of the latest sail designs and construction, Spindrift 2would need a new mast – and that meant a completely new design along with new manufacturing tooling. That is where HDS-GSEA Design comes into play: specialising in structural calculations of complex beams, particularly masts, and other composite structures, our company is now among the global leaders in an increasingly sophisticated field.


Test phase


The original mast was designed around the moulds used to build the spar for Franck Cammas’s previous Jules Verne winner


Groupama 3, largely for reasons of cost. We already knew this mould shape was not optimum for our much bigger boat, and based on my personal experience of big offshore multihull spars I already had ideas about where development would take us. Beginning in 2013, we agreed with Spindrift to fully instrument their 40m trimaran’s rigging. We then conducted sea trials that allowed us to validate at full scale the accuracy of our existing rig simulation tools and calibrate them as accurately as possible to this specific boat.


Yann Guichard’s team’s decision to race the 2014 Route du Rhum with Spindrift 2 gave us another excellent opportunity to investigate the improvement options for a future spar. As a first step, the original 44.5m spar was shortened to 38m for the singlehanded Rhum. This meant we could also take our first steps towards exploring a new sail plan. We shortened the giant spar, built new sails, adapted the rigging and chainplates and were ready for Yann to set off across the Atlantic – the whole boat now littered with fibre-optic strain gauges.


The data the team brought back to us following the Rhum was also then compared with our modelling, giving us sufficient confidence to begin the design of the new mast. During this phase our own calculation tools were also constantly being improved, calculation methods, solvers, loops. Plus we improved the reliability of our tools to allow more accurate extrapolation of the results of shorter test sessions on the water to ‘around-the-world’ conditions.


Ultimately the testing phase extended to almost two years, but the end result was a strong foundation for designing a new spar (and making other improvements around the boat), as well as giving increased understanding for the race team of how to make their boat perform to the maximum. Integral to all this data acquisition also came a mass of information to assist the design of the boat’s new Jules Verne sail wardrobe.


Down to work


The scope of works was simple… ‘deliver the best possible mast for the boat and without any parametric constraints’. There are three principal parameters when optimising any mast:


SEAHORSE 45 


BENOIT STICHELBAUT


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