How to develop a perfect sail inventory before a boat has been built

In fact preparing a wardrobe of sail designs for a still to be launched performance yacht is not so hard... if you have the tools for the job

How do you develop the perfect sail inventory and sail shapes for a boat that hasn't even been built? We’re talking about X-Yachts’ new XR 41, the company’s first pure raceboat for a number of years which is intended as a pivotal model that will take the Danish yard back to its roots as a builder of championship-winning production yachts. Chris Williams of North Sails says the best route is always to start the process at an early stage of the design phase.

The goal of winning a podium place at the 2025 ORC world championship in Estonia demands that this design performs to the optimum right out of the box. ‘Being involved at an early stage allows us to avoid compromises and ensure that the sail and rig setup is optimised right from the start,’ Williams says, ‘rather than making adjustments later.’

Williams has huge experience in this field, with notable projects including the Melges 40, as well as custom boats such as a Carkeek 40, 47 and 60 and several TP52s. For the XR 41 he’s bringing the design processes associated with these grand prix style racers to a production yacht. This may be an unusual step, but the final outcome will bring massive benefits to XR 41 owners.

As part of the process, for example, Williams says they modelled different rig sizes, checked different headsail versus mainsail areas and even analysed the best fore and aft position for the mast. ‘This project definitely benefited by getting North Sails involved early and not just being given the sail plan and told to make sails that fit those dimensions,’ he adds.

It also enabled the design team to follow trends in some of the more established grand prix classes and as a result the XR 41 will have many of the cutting edge features that you would expect of a custom raceboat, even though it’s a production design. For example, at this level it’s becoming the norm to sail with more mast rake while using mast step shim stacks aggressively so that you don't need to pull the headstay tight to tension the rig. The North design team will also work with the sparmaker to ensure sail shapes are optimised for the mast stiffness and headstay tension targets, as well as the spreader sweep angles and geometry of the rig.

Williams says they ran about eight different rig geometries to find the optimal configuration. This process also involves checking the performance of sail shapes across a range of wind conditions – six, eight, 10, 12, 16 knots and upwards – ensuring that the sails perform optimally in all scenarios.

He also highlights the importance of integrating sail design with the rig and both keel and rudder design. In addition to top sailors including Bouwe Bekking and Jesper Radich, the North team is also working with KND’s Roland Kleiter, whose inputs including the fine tuning of the appendage sizes to make sure everything's perfectly balanced.

The design team also has the huge benefit of access to the North Design Suite, which allows for precise modelling and adjustment of sails and rigs throughout the design process. The software packages cover sail shape (Spiral), sail structure (Warps), rig design (Desman), computational fluid dynamics (Flow) and flying shapes under load (Membrain).

The starting point is Desman, which creates a virtual 3D model of the boat and rig. It allows every element of the rig to be modelled, including shroud sizes, mast stiffness both longitudinally and athwartships, as well as the geometry of everything from the spreaders to backstay and shroud locations. ‘This gives us a really accurate model of the mast that we can combine with the sail shape and structure outputs,’ says Williams.

Spiral then allows three-dimensional sails to be placed on the Desman model before wind pressure or load are applied. Every dimension of the sail can be precisely adjusted.

‘Warps is a really powerful programme that allows us to put structural tapes anywhere we want in any density or orientation,’ adds Williams. A large catalogue of different tape styles allows designers to choose optimal ratios of different materials, including carbon and Dyneema, to give the sail exactly the properties they desire.

Flow introduces wind pressure to the sails created by Spiral and Warps. Pressure varies across the sail’s surface based on the specific design and the strength and direction of airflow. Membrain balances wind pressure, sail shape, and rig forces using data provided by Flow to deform the aero package as a unified structure. New data is then sent back to Flow for optimisation by the sail designers.

This enables the designers to trim and tune the sails, making all the adjustments that are possible when afloat, with changes in loads of standing rigging, sheets, and so on calculated continuously. It also shows designers the flying shapes of each sail at a variety of heel angles, traveller locations and apparent wind angles. They can even alter halyard and outhaul tension to see the differences in sail shapes, as well as determining the differences that variation in rig tune make to sail shapes. This is a critical factor given the significant influence rig tune has on sail shapes.

This stage of the design is an iterative process, so Williams says they typically carry out a few loops, improving the sail shape and optimising the trimming each time. ‘One of the nice things about the North software,’ he says, ‘is each loop can be very quick. If I design a mainsail with the draft too far forward because it has too much luff curve, for example, it only takes 10 minutes to redo the whole model and try a sail with different shape inputs.’ The software also means the North Sails team can provide detailed tuning guides even for a one-off or prototype boat.

North’s 3Di technology means the exact designed shape can be transferred to the finished sails every time. ‘What we design is very close to what we see on the water,’ says Williams, ‘as the robotics used for making 3Di sails means we build the sail with really high precision.’

3Di also offers an enviable blend of performance and durability so it’s ideal for the XR 41 project. A key benefit is that the designed shape is retained as the sail ages, even after many thousands of miles. It might cost a little more initially than other options but its excellent performance and longevity offer great value to owners. ‘3Di provides a unique blend of performance and durability,’ Williams says. ‘The sails’ ability to maintain shape and performance over time offers great value, especially for sailors competing in diverse racing environments.’

The sails for the XR 41 will also benefit from Helix, North Sails’ Structured Luff solution, which simultaneously reduces halyard loads and luff sag, creating a more aerodynamically efficient flying shape. The mainsail, also Helix, offers better shape retention, load distribution and easily repeatable sail trim settings using a hydraulic cunningham.

The shift from traditional pinhead mainsails to square top mainsails also brings significant performance benefits and, while the XR 41’s mainsail won’t be as extreme as that of a TP52, it will be larger than existing typical ORC designs. Benefits will include improved light air performance, quicker acceleration off the start line, out of tacks and at mark roundings, as well as enhanced downwind speed.

What does it feel like when the sails first go up on a new raceboat? ‘As accurate as our tools are there's always a little bit of excitement,’ says Williams. ‘This is a year-long process by the time the first boats launch and it’s always part of the learning process for us.’

How much did the typical weather conditions at the venue for the 2025 ORC World Championship influence decisions about the sail inventory and sail shapes? ‘If you want to win a championship, you need a really good all-around boat,’ says Williams. ‘It's easy to win a single race if you make a boat that's really good in light air or really good in breeze, but the goal here is to have a really good all-rounder.’

That's also great news for owners who want to take their boats to different events. They benefit from the reassurance their vessels will be just as well set up as the professionally sailed works boats and that their sail inventory will remain just as competitive the following season.