Luna Rossa flies, but why that apprued trim? VIDEO

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The occasion is the launch of a preview video of the April 2020 Cagliari races, April 23-26, a true America’s Cup appetizer, and for the first time we see a little more than one-minute video of Luna Rossa in the air. The images are carefully taken without zooming in, from very far away, yet they are nonetheless interesting, both for the glimpse of the Italian boat under sail and for some of the technical details that emerge.

https://www.facebook.com/LunaRossaPradaPirelli/videos/1433261236823034/

What are we talking about? First of all, about the “apprued” trim that had been seen before in the Bermuda catamarans and is being revived on the AC 75s. The reasons are aero- and hydro-dynamic in nature: taller boat=less submerged foil, more risk of turbulence around the appendage, and consequently less control with the possibility of “pruata” in the water. In broad strokes, a comparison can be made with the “spinnout” in windusrf, although other factors also intervene in that case. In addition, it seems that choosing this downward bow trim is also important to reduce drag (resistance in the water), and the resulting turbulence, of the rudder at high speed. The important thing is that the short side of the T does not get too close to the water surface.

In addition, if the boat flies slightly with the bow upward, it increases the aerodynamic drag of the hull, which multiplies the risk of pulling out the foils. Giving an elementary example: let’s imagine if on the highway at 100 kmh we pull our hand out…If we hold it shear, straight, cutting through the air, we manage to hold it sufficiently still, if, on the other hand, we pull it up a bit by offering the greater surface area of the palm to the wind our arm is pulled upward). Of course, what we hypothesize are entirely partial explanations, which do not claim to be entirely correct, but they may give a minimum idea of the set-up we see in this video, and also in those published by Emirates Team New Zealand.

Mauro Giuffrè

 

 

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