SVN solovelanet

49 SVN Solovelanet Global However, AC75 will go even further. The dou- ble mainsail will most likely go all the way down to the main deck, a few inches from the maneuver area. That's why the main deck is still a highly strategic topic and each team has a strong interest to make it as flat and uniform as possible. But maybe the most interesting advanta- ge of this revolutionary mainsail is that it is conceptually split into three sections. Of the 87 feet of the mast height, the crew will be able to control basically every aspect of the mainsail on the first 8 and on the last 12 feet. Among all the teams, Luna Rossa seems the one who dares the most, going without a pro- per boom. Instead, the mainsail base looks like being controlled by a complex system of sheets and mechanisms. Still a lot is being speculated over this system and not much has been disclosed. Moreover, the mainsail head portion is adjustable and allows for shape control. On so doing, for example, it is possible to have a really powerful mainsail in the bottom part, while the upper part not only less loaded, but even producing downforce when needed. This trick is key in the starting phase. Let's see how. First step: take off Thanks to many videos and computer rende- ring shared by each team of social networks, we already have a clear picture of the AC75 when flying. However, what we still don't know is how those boats can reach such flying condition starting from zero speed. Paul Goodison, world and Olympic champion and American Magic's wing trimmer, shared some interesting insights about how hard the ma- neuvering of the AC75 can be. When the boat is still, the foils are set in their resting position under the boat. In such con- figuration, they act like a traditional keel with an overall weight between 2.5 and 3 tons, which is not that much for a 75 feet monohull with such huge sail area. If you tried to gain speed by trimming both sails like you would do on a normal boat, you would probably end up capsizing pretty soon, given the poor righ- ting moment provided by the keel-like foils. It would be preferable to ease the mainsail and open the windward foil a bit. M athematically, the (linear) moment of a force F, applied on a point P with respect of a center of rotation O is defined as the product of the force magnitude and the distance, perpendicular to the force, between the center of rotation and the line where the force is applied (see Figure 3). This is also called torque. Note the following: ● The further the force is applied from the center of rotation, the larger is the distance, the greater is momentum; ● Likely, the same moment can be obtained by a smaller force applied further away, or from a greater force applied closer. Intuitively, a moment is the ability of a force to make an object rotate around an axis. In a sailing boat, the wind makes the boat roll around its longitudi - nal axis by applying a rolling moment when hitting the sails. This moment is compensated by the so- called righting moment generated by the foil or the keel. According to what we said before, we note that the distance between the keel and the longi - tudinal axis of rotation of the boat is shorter than the one between the axis and the center of forces applied on the sails (sail center). However, this is not the only moment acting on the boat. When referring to mainsail and jib as "tacking sail" and "bearing sail" respectively, we state the intrinsic tendency of these two sails to apply a ya - wing moment around an hypothetical vertical axis. When these two opposite moments compensate each other, the boat is in equilibrium. Lastly, the jib can sometimes generate on the boat an annoying pitching oscillation which cannot always be miti - gated by the mainsail. So far we said that the ae- rodynamic force can be decomposed into a parallel and a perpendicular component with respect to in- coming wind. Actually, there is a third component in the vertical direction, much smaller than the others two, that "pulls" the bow vertically. This is the rea- son why, by sailing close-hauled with strong winds and moderate waves, the use of a small staysail can be beneficial in terms of reducing the pitching oscillation. In fact, in this way the distance between the sailing center of this sail and the mast is redu - ced, hence reducing the moment (see Figure 4). The righting moment

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