Dynamic lift(downforce): Cat vs Tri-

Discussion in 'Multihulls' started by Doug Lord, May 1, 2019.

  1. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Vincent Prevost sheds some light:

    Excerpt 1:
    But when it comes to foiling multihulls , we can rest the question. Because the moment of recovery, it can also be dynamic (see box): with a trimaran, you can pull down on the drift of the central hull, and on a catamaran you can shoot the rudder which is in the wind - no need to use the big foil, saffron is largely effective enough. If we take an Ultimfor example, we can quickly gain 20 tons-meters, if we pull 2 tons on the central hull, since roughly the half-width of the boat is about 10 meters. On a moment of recovery of 150 tons-meters, it's already good. But on a catamaran, it's even better: by pulling 2 tons on the rudder in the wind, the lever arm being 20 meters, you win not 20 but 40 tons-meters. Or we could win as much by shooting twice less. It's interesting because we end up with a kind of gearbox: instead of shocking the mainsail cart, we can change the incidence of foiland it may be easier to move the flap of a carrier plane than to change a carriage position. And again, at these speeds, with small surfaces of planes on a central drift or a saffron, we arrive fairly quickly at 1.5 tons or 2 tons and we can gain 25% of recovery moment, this which is huge.
    Excerpt 2:
    Let's move on to dynamic RM. It is simply a matter of using the lift of a foil instead of the weight of the boat. On a multihull, you put a foil in the wind or on the central hull and it is given such an impact that it pulls down instead of pushing up. On a monohull, we put a foil under the wind and this time, to make the dynamic RM, instead of pulling down to the wind, we push upward leeward. "Dynamic RM is something new that redistributes cards," says Vincent Lauriot-Prévost . Whether for multihulls or for monohulls, by the way.
    Manfred.pech likes this.
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