Wing Driven Thing
The K8 is new sportsboat design powered by a cleverly designed and easily manageable wingsail that makes it capable of planing upwind and down. Intrigued? So were we, so we tracked down Bret Perry from Katabatic High Performance Sailing Solutions to find out more.
Sail Racing Magazine: Sum up the concept behind the K8.
Bret Perry: The K8 has been designed with ease of sailing in mind in order to attract a wide range of sailors. It is unique in that it’s powered by the world’s first production wing sail – a.k.a. the Semi Rigid Wing (SRW). The K8 has a modern hull design that is easily driven to planing speeds, both upwind and downwind. The hull is optimised to take full advantage of the wing sail and this delivers a fast yet highly stable race boat.
SRM: What type of racing sailor do you think the K8 appeals to?
BP: Our research tells us that many high-end performance sportsboats end up not being sailed because they require an athletic crew of around six people to sail them effectively. In contrast, the K8 is all about ease of sailing. It has a crew of four who sail the boat facing inwards – no ‘legs-over’ hiking is allowed – making it appealing to a wide audience.
The K8 is a technologically-advanced yacht that delivers great performance courtesy of the the semi rigid wing rig. The wide, chined hull provides great form stability and the wing drives the boat along easily in even the slightest of breezes. Twin rudders make it easy to steer even at pronounced heel angles and the wingsail adds a new dimension to the sailing experience. While it’s easy to quickly get the boat sailing fast, getting the most out of it requires some additional thought and learning some fun new trimming techniques.
Putting all this together, we believe the K8 will appeal sportsboat sailors who are sick of their bodies being beaten up every weekend, but who still want to get around the course quickly and have fun. The K8 punches well above its weight in the performance department, making it an attractive option for owners looking for a big boat feel but scaled down to a traillerable boat with a smaller crew and lower running costs.
SRM: Tell us about the team behind the K8.
BP: We have a four-person team managing the development, production and marketing of the K8.
The SWR was designed and developed by brothers Greg and Patrick Johnston, the two founders of Advanced Wing Systems.
Greg Johnston is an engineer with an MBA who has sailed all his life on everything from 18’ skiffs, Etchells, ocean racers and America’s Cup 12-metres. He is responsible for the detailed design, including the CFD and structural and component design. He also has 30 years of experience sailing with the SRW in various prototype forms.
Patrick Johnston is a shipwright and was behind the design concept at the heart of the SRW. He is now responsible for production co-ordination of the SWR and the build of the K8.
G Yacht Design’s Nicolas Goldenberg is naval architect who embraced the SRW technology early on. His RG650 Classe Mini 650 boat was the first ever completely international design to reach series/production status and now has 15 boats built.
I represent Katabatic High Performance Sailing Solutions and I have been a professional sailor for over 20 years. I’ve got 10 Sydney to Hobart Races under my belt and have worked on myriad of other international projects including America’s Cup and Volvo Ocean Race campaigns.
SRM: Explain how the Semi Rigid Wing system works.
BP: The SRW system is based around a highly aerodynamically efficient rotating mast. The wing is formed by two, fully-battened membranes that are flown from twin tracks on the back edge of the mast. From a distance, the SRW looks very much like a conventional rig and often people don’t immediately realise it’s a wing.
The SRW has been designed from the outset with practicality in mind. From a sail handling perspective, the system is not dissimilar to a conventional mainsail. It’s designed to be rigged like a normal mast with a forestay, side stays and spreaders. It’s also hoisted and stowed in exactly the same way as a normal mainsail. Each membrane has its own halyard but they combine inside the mast so one halyard can be used for hoisting.
When you are sailing, the shape of the wing is induced by mast rotation and the batten tension setup of the membranes. It’s very simple to get your head around; on port tack you rotate the leading edge to starboard and on starboard tack you rotate the leading edge to port. The counter-rotation action compresses the leeward battens, forcing them into an aerofoil shape – the more rotation, the thicker the wing.
The biggest differences compared to a conventional sportsboat rig come in how the wing is sheeted. Traveller sheeting is the main means of power control. Adjusting the traveller effectively changes the angle of attack of the wing, while the mainsheet is used to control twist and is more akin to a vang on a conventional sail. The outhaul is used to adjust the wing’s camber.
To make it more interesting, there are also two new controls: one for mast rotation, which affects the wing thickness and therefore its camber; and a control to adjust the section thickness in the upper part of the wing.
The SRW is a true aerofoil wing section, so it has quite different characteristics to a conventional mainsail. The mast on a conventional sail disrupts the flow at the worst possible point – right at the front of the sail. On the SRW, the mast forms the leading edge of the wing and has quite different flow characteristics. The power comes from the front of the wing, not the leach, so to achieve optimum shape you are always trimming for flow around the leading edge. This difference alone requires a bit of relearning at first, as the tell tails can be lifting for a significant part of the back of the wing and yet it is still working.
Essentially, you set the shape of the wing for the conditions and then trim angle of attack to control the power.
It’s the same trimming technique that modern America’s Cup sailors use - although of course, I am not suggesting that the SRW is as efficient as the very sophisticated double-element wings used on the AC boats.
SRM: Wing sail systems have never made it into production boats so far. What makes this system different?
BP: Greg and Patrick Johnston are the brains behind the SRW and have been working on the system for near on 30 years. Previously, soft wing designers have been seduced by the idea of a mythical wing which has the ‘perfect’ leading edge required for laminar flow. However, the reality for sailboats bobbing around out on the sea is that laminar flow is almost never achieved.
Turbulent air flow, where there is a very thin layer of disturbed air on the surface of the wing, is far more robust concept which can negotiate bumps and imperfections like sail tracks and sail stitching without breaking down or detaching from the wing.
The SRW works on the principle of inducing turbulent flow early, meaning we can incorporate practical design considerations, like hoisting, stowing and reefing.
Also, the K8 uses a jib and gennaker that has been designed specifically for the SRW and could also fly spinnakers and code zeros if required.
SRM: Describe what it’s like to sail the K8.
BP: One of the first things people comment on is the lack of noise from the wing. No matter what you do, there is no flapping or flogging noise.
In light airs the K8 can sail at close to wind speed in every direction. Even when it gets so light that other boats are wallowing or drifting, the K8 just keeps going.
As the breeze picks up the boat is quickly propelled to boat speed upwind and beyond wind speed downwind. Picking your upwind angles is important, as it is possible to sail the boat high and slow or low and fast, much like you hear the AC guys talking about their modes.
Because the wing does not luff, in the gusts you can simply point the boat higher (effectively reducing the wing’s angle of attack) enabling you to gain height. The limiting factor is the headsail which will eventually begin to invert. However, in strong puffs a skilful helmsman will be able to drive the boat over the headsail to keep the boat on its feet and make large height gains against conventional boats.
The wing performs really well downwind too, particularly once you are planing. The gennaker is flown from a fixed sprit and optimised for use with the wing. Trimmed right it can help the wing keep working at true wind angles deeper than 150 degrees. We have regularly seen a consistent 15 knots of downwind boatspeed in no more than 15 knots of breeze.
The big differences people notice when they first sail the K8 are the stability you get from the SRW and the ease with which you are able power up or down. Also, because of the stable and forgiving nature of the wing, it stays powered up even if the boat pitches and rolls through waves or you are punching through chop.
SRM: What is the regatta schedule for the K8 in 2016?
BP: We plan to have a K8 in Cowes for the J.P. Morgan Asset Management Round the Island Race, and at the inaugural IRC European Championships at Cork Week. After that we hope to head back to the Isle of Wight for Cowes Week.