A few years ago the BBC showed a documentary about a group of aerospace engineers attempting to recreate Da Vinci's flying machine. Using their knowledge they realised that a long narrow wing would be more efficient than the "fat" wings in the original design.
They wanted some authenticity about the design though for the sake of appearances, and so attached fabric strips about 30cm wide off the trailing edge of the wing to create the outline. When testing this design they found that they had, accidentally, made the wing even more efficient as the flexible trailing fabric held the turbulent flows from the upper and lower faces of the wing apart and reduced drag. If my memory serves I think they increased the range as a glider by about 15%.
Could some form of flexible trailing edge be attached to the foil? Obviously with the wedge you have significant vorteces on the trailing edge that help create the effect you desire, but the quantity of spray shown in the videos you have posted indicates huge energies when these vorteces collapse. The flexible trailing edge could reduce this while creating a pathway for air along the trailing edge.

Just a thought in a teacup! Probably rubbish....

Good luck anyway, it's been fun following your progress so far, can't wait for 60 to appear!

 Hi Sclynch,

Your understanding isn't quite right. Think of the foil in three sections, the FIRST foil is the upper long section which connects to the boat. The TRANSITION is the curved bit which curves through 90 degrees and the SECOND foil is the lower part whick extends to the tip.

The first foil is at 30 degrees to Horizontal, the second foil isat 30 degrees to vertical so that it is parallel with the wing on the opposite side of the boat. The transition foil curves through 90 degrees to join the two.

HERE YOU CAN SEE THE NEW FOIL OVERLAID ON THE OLD FOIL TO SHOW THE DIFFERENT SIZES. YOU CAN ALSO SEE THE LOW SPEED WATERLINE AND THE HIGH SPEED WATERLINES IN DARKER GREY CLOSER TO THE TRANSITION.

Right, so how the boat generates its ride height is typical of a true surface piercing foil (like Hydroptere)... but slightly different in our case. It should be noted that the foil is fixed rigidly to the boat and has no moving parts. As we start moving the foil is deeply submerged as illustrated by the low speed/static waterline above. A large part of the first foil is in the water.This is producing predominently upwards lift... and a small amount of lateral resistence. The second foil is basically opposing the wing forces although the lift from the first foil will result in net 'up-thrust'. VSR2 will rise out of the water and keep rising until the vertical lift generated by the wing and what remains of the first foil equals the down-force generated by the second foil and the static weight of VSR2 at the back. Basically we only need enough of the first foil in the water to lift the static weight of the boat. This is not much. A human can bare foot waterski at 35 mph. Anything more than this amount is just pure drag.

So, part of the wings thrust is lost in generating lift and part of the foils drag is generated in opposing it. This is an issue with the Bernard Smith concepts. In order to get both the wing and foil upright and have no vertical losses, you would need an infinitely wide boat. The dimensions of VSR2 are determined by the angles where you get diminishing returns i.e. 30 degree inclinations. This may all explain why we may never be quite as efficient as say Yellow Pages or Mac. Innovations... although we aren't too far off and we should have a lot more stability and power. I'm a fan of those two boats by the way. Brilliant boats well executed.

So, there will always be some rearward component generated by the drag associated with pulling the boat down... but it is understood and accounted for. What may not be quite so well understood is the loss of lift generated by the first foil so close to the surface... given that the first foil enters the water at such a shallow angle. We need to play with this. Also there are plenty of very subtle little twists and changes in foil profile in this area which also need to be dialled in. Remember also that the whole angle of the foil changes as the back does start to lift as the whole boat is pivoting 'pitch-wise' around the forward float. A change in pitch will have greatest effect on the first foil than the second... as it is more horizontal. We will continue to adjust settings to see what we can do to get VSR2 riding as designed in the most efficient manner.

Cheers, Paul.

 Yeah the cameras are getting smaller too Macca. The boat is similar to the grey nurse in some respects i.e. mostly sideways... but hopefully this one doesn't go over the top as often... and there's less dodgy stuff behind the seats!

I'm gettin mate... I'm gettin.

Cheers, Lars

 We have built a pretty serious VPP (Velocity Prediction Program) over the years for this boat. We did a nice big feasibility study at the start of this boat before we committed to the design. No point wasting time on a turkey. I am confident from a project managers point of view that we have had the right people with the right skills involved to monitor the VPP and its development. We are generally pessimistic about our inputs and try and include every aspect of what might ultimately contribute to overall performance. This includes things like wave height, spray drag, added weight etc. I don't have to weight long when I enquire about the effect of changing one parameter. Our VPP is pretty in depth.

VSR2 was basically designed to be the platform most likely to be able to drag the worst performing foil down the course at high speed in a variety of winds. She is a tough, powerful, stable and very efficient craft. The design speed is 65 knots. Everything about this boat is designed for life at 65 knots including the wing areas and fuselage orientation. Throughout the design one of our biggest worries was the ability to get to 65 knots... and this means sailing at 0-10 knots. You always have to compromise for these speeds at some stage.

So we assumed the worst case scenario for foil package i.e. an L/D of 3.5 and worked out how much power we needed to drag that down the course at 65 knots. This gave us an idea of what the wing had to do. throughout the build we generally tried to tweak the whole boat in our favour. 

Right now we still think we have the right foil... until we have run out of options. As mentioned, it only has to perform poorly to achieve 60 knots... but something is happening that won't even let us get to the mid 50's. We need to keep working through a process of elimination in order to find out what it is. The back of the main foil seems to be working fine. we are about to have a look at the rudder. Maybe it really is just a bunch of smaller cumulative things. We have the tools to find out. I hope we have the wind and time.

Cheers, Paul.