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One look at the Gunsails BOW sail tells you it’s different, very different! It has a specially developed mast to go with its radical head design and in contrast to established modern designs, doesn’t have a loose leech. To get the lowdown on the BOW and find out more about its design, we caught up with designer Pieter Bijl.

 Words Finn Mullen, Pieter Bijl. // Photo Pierre Bouras / Gunsails

WS: What is the BOW concept?

PB: The BOW concept is based on a new sail outline with an extreme bend curve at the top. This extreme curve is only achievable with the BOW FLEX mast. Due to the low luff tension and the innovative design, the sail does not have any loose leech. Thanks to a special friction bearing, which allows the mast to rotate within the boom, the mast can rotate inside the sail, thus allowing the upper area of the sail to twist and bend away. In contrast to the ‘Loose Leech’ concept, where only a small part of the leech twists, the BOW has a much larger area to adapt to the strength of the wind. When the wind strength and thus the wind load in the sail increases (high loading), the upper part of the sail turns leeward and the profile adapts dynamically. The holding forces on the boom remain the same. Only the profile adapts to the higher loading. When the wind force and thus the load in the sail decreases (low loading), the sail turns back to its original position. Now, the lower wind energy is compensated for by the more efficient profile. The drive, as well as the holding forces, remain the same. This ability facilitates handling enormously and also improves performance while going upwind. The described adjustment of the BOW is more dynamic and effective than the ‘Loose Leech’ mechanism. Due to the well defined and firm edge at the leech, there is no fluttering and the associated small stalls in the profile. Similar to a ‘Loose Leech’ sail, the BOW regulates itself in gusts and wind holes, but the available area is larger and more efficient. Thus, it covers a much larger wind range in total. For the windsurfer, this ability leads to an effortless and comfortable windsurfing experience, combined with the performance and drive of a camber sail. Due to its continuous drive and light handling, the BOW sail is predestined for foiling.

WS: What are the innovative features?

PB: We have been working for 2 years on this concept before bringing it to the market. During this development we were always shown the potential, but obviously when making something new you aren’t always making a step forward, but there were always qualities that were not only unique to the concept but more so very motivating to push forward. During the second phase of the development the concept really started to take shape. It was clear what parts and features where needed and more importantly, what could be discarded. The innovation is how the mast bends with the leech of the sail, allowing us to design the sail with a minimal amount of twist. Normally so little twist would kill the sails high end on a traditional sail. But with the mast bending so far back in combination with the mast being extremely soft in the top we have a constant increasing and decreasing twist depending on the lateral pressure of the wind. Then to even more enhance this effect of progressive and proactively adapting to the lateral pressure we added a rotating mast shim that allows the mast to rotate inside the boom head with reduced friction. With this rotation the sail really comes to life. The fine adjustments are done through the torque that the wind puts on the mast and the large adaptation to wind strength (lateral pressure) taken care of by the rotation device inside the boom head.

WS: How did you develop and refine these features and what benefit do they give?

PB: The development of this concept and its parts and features was simply a part of the testing; feeling and coming up with simple new solutions to enhance the strong points of the sail while trying to eliminate the bad. The big benefit of the BOW sail is how it adapts to the wind strength. Low wind will see the leech tighten up and actually pulls the centre of effort back to give the rider fin pressure when he needs it. In high winds the sail opens, releases excessive pressure and brings the draft forward to give a well managed amount of fin pressure and so keeps you in control for longer. On traditional sails, normally the centre of effort moves back in the upper end of their wind range, and with that the fin pressure increases and the lift increases up to the point that you can’t control the power. On the BOW sail, the sail actually starts to give downforce in the upper end and with a controlled amount of fin pressure you remain in control. Of course everything has its limits, but we strongly believe the wind range of the Gunsails BOW covers two traditional sails with one size.

WS: Were there any interesting milestones or workarounds in the R&D process?

PB: The mast bending and durability were of the highest concern, our challenge was how do we make a mast that allows such extreme bending? We wanted a mast that was still responsive but yet soft, so we worked a lot with our mast guys and created some interesting constructions to ensure the mast was doing what it needed to do and all that without breaking. Also the rotation bearing, when we started using this it was another eye opener to what is possible if one can come up with a simple, easy and innovative solution.

WS: Where do you see the product fitting into the market?

PB: It is a fast sail but not a racing sail just yet. I have no doubt this concept will be used in racing as it matures. However, for the moment the sail is well suited for riders who are looking for performance (freerace to racing) with incredible wind range and with great handling. The BOW has four cambers, it is therefore initially aimed at sporty windsurfers who use cambered sails. We currently need the camber in the BOW more in order to achieve the desired shape, less for the sake of driving performance. The next step for us in design is to transfer the BOW concept to a camberless freeride sail. For foiling, this sail is one of a kind, to have a sail that offers lift in light winds and downforce in the upper end allows you to foil much more
comfortably throughout a bigger range of conditions.

WS: Do these sails work with normal masts?

PB: Absolutely not possible. The mast is a uniquely designed piece. A normal mast would never be able to handle the BOW’s level of bending.

WS: What are the sizes available and price?

PB: For the first release our goal was to keep it as simple as possible, innovation is meaningless without simplicity! So to allow riders to get into this concept we have released three sails 6.9, 7.8 and 8.7 that all fit on one mast. With this sail range you will cover from 8 to 30 knots easily. If you want to get two sails the 6.9 and 8.7 will give you that range. If you want to sample just one size then the 7.8 will start you up at 10 to 12 knots and I pushed it well past 35 knots, where the sail was still controllable on the straights but became too much during the gybe. Prices – BOW 6.9 for €669, BOW 7.8 for €679, BOW 8.7 for €699 and €399 for the 490 mast.

For more information on the BOW concept, see www.gunsails.com/en/BOW2019.

“ We strongly believe the wind range of the Gunsails BOW covers two traditional sails with one size.”

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