Our first Foil Moth: Svelta.
Our first boat!
Its innovative design is based on an inner frame in glass and flax fiber able to withstand all the main mechanical stresses. Consequently, the outer hull pannels are just close the volume and guarantee buoyancy.
Thanks to the simple role given to them, we opted for eco-sustainable panels in Flax-PET sanwich. Its outer layers are made of aesthetic blue flax fiber, visible on the hull surface.
The wings are made with upcycled carbon fiber rowing oars, offered by the canoing team of Pavia.
The tubes are connected with bolts and nuts, using pure resin peaces collected from discards for nuts’ cushion purpose.
The mast base is made of the fore mentioned broken tubes, which are connected thanks to a flax fiber bond made by hand with no vaccuum, exployting the fiber bonding tension to guarantee a good layer adhesion.
The mast invitation is made in pure resin from discards, using gypsum as a Bladerider calc and a glass as container during various lamination processes where could be resin excess to discard.
The mast, boom, sail and foils comes from a Bladerider, shown below.
Our Bladerider®
Learn, Train and Fly.
As a new team, the presence of a state of the art foiling moth permitted us to learn and train from the beginning.
We bought a 2010 Bladerider for several purposes: mainly to permit the training of our skippers, contemporarily with the boat production, but also to experimetally understand the boat’s features and list all the aspects we reputed important to be mantained or to be innovated in the new models.
With an innovation focused on the hull production, the 2010 model permitted us to reuse the most cost effective parts in the competition: mast, boom, and foils are usually made of carbon fiber due to the enormous stress those parts are subjected to.
The reuse of old parts or discard/recycled materials is foundamental in eco-sustainable prototyping.
How does a foiling moth work?
The main forces that must be considered on the centreboard, rudder and respective foil components are those of drag and lift. The first is the component parallel to the flow, which tends to drag the object in its direction; the second is the force that tends to lift the object. What creates lift is the pressure difference created between the back and belly of the airfoil, formed by the moth’s wings. Considering a wing with finite elongation, due to the pressure difference, near the end of the wing the flow will tend to curl, forming vortices around the end of the wing itself.
These vortices downstream of the wing create a small downward component, called downwash. In turn, the downwash will add vectorically with the speed of the uniform current, thus producing a local downward sloping current near each airfoil. The angle between the chord and the actual speed is therefore no longer the geometric incidence, but the induced one generated by the downwash is subtracted.
Consequently, the effective lift will also be inclined by an angle αi compared to that created by the undisturbed flow. This causes a lift component to appear parallel to the undisturbed speed, i.e. a drag component also due to the downwash. This component is called induced resistance.
At the bow of the hull there is a rod that falls, due to the effect of gravity, downwards. Depending on the height at which the hull is located with respect to the free surface of the water, the rod is more or less inclined with respect to the horizontal. This means that we have information on how far the boat is from the water. The information is transferred along the hull via a mechanism which rotates the edge of the foil, varying the lift more or less. If this adjustment mechanism were not there, the foil could push the boat into the water or make it jump out like a dolphin.
In addition to this, the boat is equipped with a second rear foil, which is governed, via the rudder, directly by the skipper. This second foil may not be equipped with an adjustable flap, but may be fixed. In this case, it is the entire rear fin that rotates through measures that are made during the design phase. The orientation of this second part serves to regulate the progress of the boat which can be helm or leeward.
The skipper must always have under control the inclination of the boat with respect to the horizontal via the rudder and with respect to the vertical plane via the hauling of the sail as well as the balance of its own weight. In fact, the sail must be positioned in such a way as to capture the wind by managing the boom. The thrust it generates tilts the vessel almost as if it were falling sideways. To counteract this, the skipper positions himself on the wings on the opposite side with her weight.
The wings are lateral appendages generally formed by tubulars of light material which, if designed specifically, also become an aerodynamic element.