Understanding the Beast
by Simon Rogers
March 2004

“If I was building a boat for the next race I would definitely commission Rogers
Yacht Design, as I did last time. Anyone considering building a new VO 70,
you should talk to these guys.” Lawrie Smith, March 2004

Comparison of the new VO 70 to the old VO 60

Comparison of the new VO 70 to the old VO 60.

Rogers Yacht Design Ltd (RYD) commenced an internal detailed design study for the new VO 70 class back in September 2003, when the new rule was published. The first stage of the process was to put together a well organised, rounded and experienced design team whose brief was to cover not only the standard technical design loop criteria of mass estimate, weather study, hull matrix, VPP, CFD, and tank work but also to give major consideration at an early stage as to how these new VO 70s are going to be sailed, built and campaigned.

The Design team

Simon Rogers Head of Design, Rogers Yacht Design
Efva Willen Naval Architect & CFD
Jason Carrington Professional Sailor and Build Manager
John Levell Structural Engineer Consultant
Hali Barber Head of Production Design, Rogers Yacht Design
Tim McDowell Production Design, Rogers Yacht Design
Lawrie Smith Contributor

Simon Rogers is well known for his innovative and successful developmental designs. Good examples of the company’s involvement with these racing machines include: Jonathan McKee’s leading Mini Transat boat, Sticky Fingers the well known record breaking Whitbread 30 and the company’s involvement in the America’s Cup with GBR Challenge. In addition Rogers Yacht Design Ltd was commissioned by Lawrie Smith for his VO 60 for the 2001-2 Volvo Ocean Race; it was unfortunate that this design did not come to fruition due to the sponsor pulling out following the ban on cigarette advertising.

Efva Willen has worked with North Sails for many years as a Sail Designer and has spent a number of years working with CFD, wind tunnel testing and tank testing. She has worked extensively with projects which include Assa Abloy, Prada 2003, and Krazy K-Yote 2 and she brings a wealth of technical input to the design team.

Jason Carrington has brought practical and build expertise to the team with his experience as build manager for Assa Abloy. He has been round the World three times and he has clear ideas on how to sail, build and campaign the new VO 70s.

John Levell is predominantly known for his VO 60 and America’s Cup rig design, but with the recent completion of the design of the entire structure for Ellen McArthur’s new 75’ B&Q, John is now well placed to take on the new VO 70 structure for RYD.

Lawrie Smith has contributed by bringing to the table his racing experience as a past skipper and this has had a significant benefit in the way RYD has approached the design process.

The Design
From my article in Seahorse in September I touched on the importance of establishing the philosophy of the new VO 70 design and the way in which they differ from the VO 60s and how they are going to be sailed. The experience we have in our design team allows us to pull on extensive knowledge of the VO 60s and from this one very important fact keeps on coming up.

The VO 60s were sailed by twelve fit and professional sailors, and the boats were fundamentally underpowered (hence the introduction of Code 0’s) and the crews sailed the boats at 100% all the time. For the first time we saw significant fatigue related illnesses, massive body weight losses on the longer legs and the boats were all very even in performance on the water. One could say that the crews were physically at 100% as were the boats: the crew and the boats were well matched.

The VO 70s will be sailed with nine crew plus a media/ cameraman, who will have to be a sailor, in a yacht that is ten feet longer on the effective waterline.They are massively over-powered (50% extra upwind/ 62% extra downwind) and between 2-3.5 tonnes lighter in sailing trim. There is no way that even the fittest of crew is going to be able to get 100% out of the boat all the time. The boat’s ability and the crew’s capability are not matched for the first time in the Volvo Ocean Race’s history. We believe that while there is obviously an advantage to be gained through good design, which all design offices are currently developing including RYD, there are potentially far larger gains to be made through setting the boats up properly, minimising fatigue and stress, and ensuring that the boat is well balanced and controllable at all times. This race is going to be all about keeping up the averages and being able to carry the sail inventory further up the wind range, in control, whilst also remaining competitive in the windward-leeward in-port races. This new class is sounding more and more like the Mini Transat class, of which we have been at the front with Jonathan McKee and Brian Thompson over the past four years.

Carrying the philosophy of control, minimising fatigue and maximising average speed in a boat that is fundamentally over canvassed, one is tempted as a designer to push towards wider designs. This has been borne out in our VPP work; however the performance in a windward-leeward in-port race favours a narrower hull, which is worth 20% of the overall points, and therefore we feel that a compromise is going to have to be found. We do not want to be the extreme boat in the fleet but be in the ball park and spend our time optimising the rig, sails and structure where we believe the real gains will be found.

Bulb weight, like the VO 60s, will be critical and we believe through our study with Jason and his experience with Assa Abloy (which had the largest bulb in the last race) a minimum weight boat is definitely achievable with a 4500 kg bulb and this bulb weight could be increased. Every kilo that is saved in the structure goes straight into the bulb and hence the bulb weight could be considered a gauge as to how well a boat has been built, i.e. the heavier the bulb, the lighter the boat has been built within the scantling rules. When one also considers that the bulb is swung 40 degrees either side of the centreline, the bulb weight is going to be even more significant to the yacht’s overall righting moment and performance.

Another major performance gain in the next race will, we believe, be in the sail inventory and ensuring that all the bases are covered whilst also allowing enough specialist sails in a very limited inventory, both on the boat and for the overall race. The polars for the VO 70s are very different to those of the VO 60s with the apparent wind much further forward; headsails and reaching headsails are going to be carried far deeper and spinnakers will be flatter and less overlapped, whilst bowsprits may be used to maximise luff lengths.

We feel that now that the gennaker (potential Code 0) has been removed and replaced by another reaching headsail, the upwind sail wardrobe has been simplified. Having said this we did not feel that the masthead Code 0 had a sufficient range to justify having it on board for all legs anyway, due to the limited righting moment of the VO 70s.

CFD calculations in the Sailview software, developed by Peter Jackson of the Yacht Research Institute, University of Auckland, New Zealand

CFD calculations in the Sailview software, developed by Peter Jackson of
the Yacht Research Institute, University of Auckland, New Zealand.

Bearing in mind that the boats will probably be reefing their mains in 12 knots of true wind, getting the sail inventory cross-overs optimised for these boats is going to be a huge task.

Appendage design is going to be critical to the balance of the boat and whilst small appendages have less wetted surface area and therefore less frictional resistance in light airs, control will be king. Currently we are working hard on appendage combinations but we feel that CBTF will not be an option. We feel that the forward rudder will be vulnerable in the Southern Ocean and whilst it may be better for the in-port races, it will always be down for the offshore legs. We think that twin versus single rudders will boil down to structural weight considerations, drag of the windward rudder and the beam of the boat. Twin leeboards versus a single centre line canard is a less obvious choice, but we feel the twin boards will track better, although they will require one crew member to tack them for the in-port races when crew are going to be at a premium.

Our deck layout is now well defined and with Jason’s input we have drawn on all our experience from the VO 60s and adapted the layout for optimum ergonomic use, minimum weight, maximum longitudinal stiffness and maximum power in the winch package. A lot of head scratching has gone into producing a deck layout that works well on a windward leeward in-port race as well as short handed in the Southern Ocean.

The rig has seen some significant changes since the recent rig weight reduction. With the rig weight at the original 675 kg, there was little reason to use PBO rigging, as the minimum weight could easily be achieved with rods, which have a smaller diameter for a given stretch and therefore less windage. Now that the rig weight has dropped to 625 kg our feeling is that the V1 and D1 shrouds will remain as rods, as they will be more resilient to wear and tear, and that the forestay could be either rod or PBO. The rest of the rigging may well be PBO, minimising fatigue in the terminations, minimising weight to achieve the minimum 625 kg overall weight and increasing the maximum strength of the rigging by 30%, whilst maintaining the same stretch. It will be good to know, as a designer, that there is a decent reserve in the rigging just in case the sail makers decide to fit a masthead flat reaching spinnaker after the boat is built, as happened with the development of the Code O.

There are so many other areas to cover like canting keel systems, internal structural layouts, bowsprits versus poles, aft water ballast etc. but the boat that wins the next race will be, we believe, the one that is properly set up, with a crew that has confidence in sailing the boat, with a well sorted sail inventory at the start of the race and not half way round. The winner may well not have the fastest hull shape, but it is going to have to be the best set up and best balanced in all conditions to allow the crew to push it to their maximum. There is an enormous amount of work to be done and the RYD team is well established to take on that challenge and is now 5 months into the design.

~End~

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