Learning from Practical Experience
The following are some of the mods and changes to the program we have made based on practical experience.
In this picture you can see the forward boom that we have since installed. It has a number of purposes. It can be used to fit mass-balancing weights on, it is used as a point to fit a forward control line as seen here so I can sheet it against the mainsheet and fix the angle of the wing in relation to the boat and it is a great place to take wind readings that relate directly to the center of effort of the wing.
The angle that VSR2 sits to the wind whilst stationary can be determined by the angle we fix the wing at using the mainsheet and forward bridle. As the wing has a mass imbalance i.e. it is tail heavy, it always tries to hang tail down/nose up and hence in a sheeted in position. The wing will keep trying to fall down against the mainsheet until it is effectively hanging off the mast in at -90 degrees. This means that if you stand on the beach holding the nose of the boat with the wind behind you, the wing will fall inwards and the boat will continue to rotate until it is almost at right angles to the wind. The wing will be feathered but the boat won’t be. To stop this we simply fit the forward bridle and fix the wing out at +30 degrees when handling the boat whilst stationary.
As it currently stands, we are not going to utilise many of the full feathering capabilities of the wing. This is due to the fact that VSR2 doesn't like to tow in a straight line behind the RIB and we don't want to tow her over 8 knots back upwind as this may add an unnecessary element of risk into the days activities. The fact is that we will typically only do three or maybe four runs in a day and we can do this by lowering the wing at the end of each run. We would rather focus on making this a fool-proof procedure than exposing our vulnerable side by towing back up the course. Where towing back up the course really fails is in the angle that VSR2 tries to sit to the strong side-wind. VSR2 tries to sit sideways. The aerodynamics overtake the hydrodynamics. As soon as the small ‘V’d’ floats are being pulled sideways, they start to lose any lifting properties they have and just become draggier. It all becomes a mess. I can lower the foils and tow the boat faster to favour the hydrodynamics... but then it really all just gets loaded up and a bit sketchy. We simply decided it was unnecessary.
We have also seen that we don't need to sheet the wing through extreme angles for general sailing. As we are no longer relying on the wing to fully feather, this means we can greatly simplify some of the systems and reduce the amount of string necessary to control it. VSR2 is getting simpler and that's a good thing.
Leward pod flying at only 38 knots boat speed indicates that the whole wing is over-inclined, especially as it is doing it with no wing flap deployment.
This wing is much thinner than our first wing on VSR1 and whilst this makes it more efficient at speed, it also makes it more prone to stalling at low speed. It feels a lot more on or off than the first elliptical wing.
We have come to the conclusion that it is more efficient to turn the whole boat to the wind during the start-up/acceleration phase rather than just sheet the wing. This is because it allows us to sheet the wing into 10 degrees where all the sections line up and thus give the greatest efficiency. As VSR2 accelerates and the apparent wind builds and moves forward I simply bear away down the course and continue accelerating. If I need to slow down or moderate my speed in order to cruise into the course, then I just sheet out to about 20 degrees until I am happy with the boats position relative to the shore before sheeting in again. At the end of a run I ease the wing out to around 30 degrees, then bear away to give myself room to turn into the wind without hitting the shore... and the turn into the wind as per any normal sailing boat. She stops relatively quickly this way.