A vortex is a whirling, often turbulent flow. Any spiral motion with closed streamlines is vortex flow. Movement of the fluid swirling rapidly around a center, called a vortex. The speed and direction of rotation of the liquid is greatest in the middle, and drops gradually with distance from the center. Vortex is a whirling wind, and that is what is generated. Theodore von Kármán (1881-1963) in 1911 described the phenomenon in which a fluids flow past an obstruction resulting in a formation of eddies alternately on one and the other side of the obstruction.

Vortex should wherever possible be avoided or minimized as the bounding vortex or force is sucked out of the effective profile. Larger vortex provides more resistance. The sail  top is the most overlooked and a important part of modern sailing. Right trimming starts from the top down because the top can have a very negative impact on both the sail and the boat’s motion in the waves. The issues are familiar but not what you can do about it.

Bird solves the problem with flexible wing tips, which compensates the difference between the vacuum and pressure moving towards the wing tip. This minimizes the vortex significantly and creates minimal resistance. Aerospace industry is today based on Winglets, vertical blade profiles on the wing tips, to minimize vortex. Winglets provide an overall, better aerodynamics and reduces wind resistance. Allows a larger mass of the aircraft, and reduces fuel consumption. Windsurfers discovered phenomenon of approx. 25 years ago. Sail twist turned out to be crucial for performance. Sails twisted / opened in the very top, but sailed faster, and was much easier to control.

Another major problem with profiles is stalling. Once a profile stalls, equalize the low pressure of lee side of the profile. The profile pull no more, and becomes a surface, pulling through the wind – a resistance. The more of a profile to stall, the greater the resistance. Vortex is formed around the tip of the profile, the sail top. The more pressure, vortex becomes larger. On a traditional mainsail vortex will move down through the leech, the more pressure, when the top is not behind the leech. In addition the vortex is forced down, bounding the effective sail surface. Sail surface stalls, and becomes pure resistance. Stalling sails is not something a windsurfer is fighting today, so that is something you can avoid.
There are currently present 3 basic methods to control the vortex at the top, and reduce the sail stalls.
• Move the leech / profiles aft upper corner at the top further behind. As an aircraft wing. (Fathead)
• Fit a transverse profile to stop the vortex’s hiking, Winglets. (Problem)
• Ensure that there is no difference of high and low pressure on windward and lee side. (Birds / E-twist)

Sail over the past several years has undergone a lot of development. The materials have been much more stable, and profile movement becomes more negligible. Also used profile battens to support the sail profile. Profiles become more defined, and requires higher demands to the crew and mates. The trail becomes narrower as the profiles become more accurate.

The traditional triangular sails with these materials is a major challenge for the crew and mate, as they must sail amazingly accurate. A task which is manageable on flat water with a steady wind. Vortex can be stabilized at the top and the sail will be effective most of the way down. Once the water is troubled and unstable winds will work with trim due to a narrow trail be a great job. The boat will most of the time not sail optimal. Vortex will wander up and down the leech, as the boat is sailing in the waves and changing sail angle to the wind. More or less resistance. It is therefore extremely important that the top of a traditional sail twist, not to create vortex, and thus unnecessary resistance. Upwind we need as little resistance from the mainsail as possible. The headsail is basically pulling and the mainsail balances. On open courses and especially with the wind the mainsail becomes more efficient. At these courses, we want more power than a traditional mainsail provides. Additional mast curvature only works longitudinal, and is forced to open the sail very much to avoid the top stalls. The traditional mainsail does not tolerate being squeezed hard.

One of the initiatives created to get the mainsail to pull more optimally in varying proportions and angles is  fathead headsail. Fathead sail plane is like a airplane wing, with the upper edge further behind. Such a corner vortex fixes and keeps it on top. To have an effect of Fathead sail, the sail is made with a bit profile. Vortex is formed over the top from the high and low pressure on luv and lee side of the sail. Wider top gives larger vortex. When the wind is going to increase the vortex is growing and increase the resistance. A flat top are still forming vortex, unless the top is angled down to the relative wind, where there is no difference of over and low pressure on the sail windward and lee side. In order to angle the top of the sail out there, is the only way to twist the top of the mast significantly (only works upwind), and simultaneously open main sheet. What we wanted to, was twisting / open the top, and keep power in the rest of the sail. Not twisting all the way up. At the same time we have a lot of sail hanging without force and profile. Sail area with resistance. A different problem with fatheat is that it very quickly restrict the boats movements up in the waves, because of too much drag in the top. The nose is forced down into the water, cut into the waves. The boat does not move freely and produces as a result of the sails, too much resistance through the water. Fathead is best on flat water, or on very large boats with lots of stability.

Generally speaking, we have the following problems:
• Traditional mainsail lacks power on open courses. Partly because of sail area, and partly because of the   mast curvature is only longitudinal.
• Traditional mainsail stalls easily and require constant trim unless the weather is constant.
• Traditional mainsail twist typical middle of the sail up to a flat top.
• Fathead have much power but too much resistance.
• Fathead rapidly becomes a problem upwind from heeling and resistance.
• Fathead react like traditional mainsail also only on the mast curvature upwind.

With EVOSION 34 and E-twist I wanted to solve the problems with the correct trim of a simple rig. A good trim for the benefit both of cruising and racers, as the boat simply sails better. Evosion 34 with E-Twist can also sail and be balanced by a small crew.

In order to solve the very issues and combine them into the knowledge I have brought from windsurfing, I have had to develop a new twist control system. One of the biggest tasks is to minimize the resistance upwind when the wind increases, and generate power downwind. E-Twist combines the benefits and solves problems!

E-twist operates with 2 halyard. One of the top and one around. one meter below. The lower fixed and the upper trims the top. The same principle as when you bend the mast top. Profiled or flat top. The flat top minimizes vortex and stalling, and with it the resistance, as the sail is twisting out to the relative wind. The best compromise to minimize resistance upwiind, increasing the movement of the boat, and maximize power on downwind. With the E-twist you can define the twister over a smaller area, and achieve the same effect. A major part of the sail, could be more effective, by sacrificing a small part of the sail. Total an increase in efficacy and a better interaction between the headsail and mainsail. The E-Twist leech should be no larger than achieving perfect twist. The need for the amount of twist varies according to wind strength, direction and sea. Twist is trimmed easily by tightening or relaxing in one halyard, an extra gear. A system that is simple to control, and not least, a boat that is easier to control.

E-Twist trim function lies in the sail, and is independent of mast curvature. Sail twist on all courses. If you want a more hollow sail downwind, close the top. E-twist works equally well on a reefed sail. Especially here, the E-twist has a big advantage over traditional trim. It is not necessary to sail with 2 halyard. The mainsail can be operated with only one halyard, and acts simply as a medium-size Fathead. One advantage of cruising.

 Acceleration and top speed is mitigation properties. Acceleration requires power. As described earlier, power is also resistance. Top speed requires minimal resistance. To take full advantage of the sails, one need a boat that can be speed up to exploit an optimal trim. If a boat is not sailing with low resistance, the sails need constant power to keep the boat going. Power associated with resistance is holding the boat from accelerating further. Evosion 34 is designed to take advantage of E-Twist optimal. A boat with little friction, and a weight distribution that allows to operate with full pressure on the rig without a full crew on the side.

This description is based only on the importance of the sails influence on the boats sailing characteristics. Sail Properties viewed as a larger and more coherent whole. Only when the designer has defined the sail plane and hull, and composite construction according to the desired concept, you start to optimize the rig, sails profiles, flow, trim as a whole and balance of the boat. E-Twist has a significant and noticeable impact on the boat’s sailing characteristics. It is obvious when you sit in the boat, and can feel the effect. I can only suggest to try first if you have doubts about the efficacy and how it works. With Evosion 34, I show that this is the start of a new generation of sailing.

“The Wing” at the BMW / Oracle trimaran is using the same basic principles as the E-twist. The possibility of moving the twister to where it has the most effect. The top is made narrow. They have the ability to open and close the top as needed. E-Twist is a similar twist konrol system. Designed to operate in a traditional mast. This is how the future of sailing will be in one or another form!

The next phase is the problems of the headsail, when the headsail basically have the same challenges as the mainsail. Vortex is also formed around the top of the headsail, and destroys the flow and power over the portion of the mainsail, which is affected by this. Rig design as we know it today does just that certain challenges. The solution is underway and I will get back to this.