Is the forward foil on C-Fly sprung in some way, or does it just look that way because of refracition?
Location: Cocoa Beach, Florida Ac 34 Lets try to keep this relevant to the AC which pitchpole is now-but pitchpole prevention is a big topic which might deserve its own thread. Location: Melbourne, Australia Quite a good article by Richard Gladwell on sail-world. For now, I'm convinced that something malfunctioned on Oracles altitude control system which is what allows them to fly.
If the system had not had a malfunction of some sort there is no doubt whatsoever that the boat would not have pitchpoled.
Great sailing days coming up with Luna Rosa and TNZ: TNZ will get to race against foils similar to the ones on Oracle. It was November 2, 2011 when the team Luna Rossa Challenge 2013 announced their Notice of Challenge for the 34th America's Cup had been accepted. Originally Posted by Doug Lord If the system had not had a malfunction of some sort there is no doubt whatsoever that the boat would not have pitchpoled. Originally Posted by Stephen Ditmore You might be right, but I don't think this is obviously true.
Location: Gold Coast Australia Hi Doug - I'm not sure how the foils can prevent a pitchpole (PP).
Location: Gold Coast Australia Hi All - Plus its an interesting hindsight that the AC72 club voted to remove the use of the small rig.
Originally Posted by petereng Hi Doug - I'm not sure how the foils can prevent a pitchpole (PP). It's my contention that the foil control system failed on 17 or the boat wouldn't have pitchpoled. Sooner or later we'll get the real scoop on what happened and why but thats my tentative conclusion for now. Location: Melbourne, Australia An interview with Iain Murray ostensibly about the new rig on the Channel 7, 18 footer skiff but also discuss San Francisco AC. Location: argentina There's no need of a greate pitch angle to get CG and Lift Force vertically aligned (see my rough sketch, over a F. Lifting daggerboards are powerful at high speed, but any small loose of speed makes them stall (lift varies with velocity squared).
From pictures, Oracle17, Lunarossa and NZ all have their front-edge daggerboards at 42-47% of hull LOA from the bow. 25 knots is not an extreme condition, my feeling is that this incident will not be the last one, unless something changes. Originally Posted by quequen There's no need of a greate pitch angle to get CG and Lift Force vertically aligned (see my rough sketch, over a F.
I don't think I'd change a thing except that part of the altitude control system that malfunctioned. As an extreme example, ice sailing sleds with vertical wings and only thin blades touching the ice can achieve an 11 degree angle off the apparent wind. With  few rudimentary calculations then  and with out calling the design teams at Team New Zealand or Oracle I calculated that the apparent wind must be about 19 degrees on a downwind angle and about 16 degrees on upwind. Given these formulas, there was no other solution than to come up with about 19 degrees of apparent wind heading downwind and 16 degrees apparent wind heading upwind. Now there are a lot of other factors that play into all this like sideslip, tide, etc and I’ve not done those calculations so please consider this as completely rudimentary.
What I’m seeing here is that the apparent wind vector is shorter than the boat speed. The following animation shows the drag force increasing with speed and the accelerating force from the wings reducing. If this really got your juices going then I highly suggest our Electronic Navigation Course.
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This image is featured as part of the article Sauter Carbon Offset Design DynaWing AC72 Schooner Catamaran – 34th America’s Cup.

Ocean Empire LSV by Sauter Carbon Offset Design – The World’s First Self Sufficient Zero Carbon Superyacht. The second AC72 for ETNZ has curved boards and there is no line on the outboard side to pull it down.
Luna Rossa launched their AC72 with straight boards with winglets and has tested S-shaped boards and boards with a kink rather than a smooth curve. Note the line to pull the board down and compare with ETNZ’s S-board in boat 1 and the curved board in boat 2. After speed testing with OTUSA in February 2012 they began modifications to increase foil lift (but not enough for full foiling) and to reduce aerodynamic drag. After repairing damage from their October 2012 capsize, OTUSA relaunched boat 1 with different foils on each hull – a straight board with an upturned winglet on starboard and a curved board with a horizontal winglet on port. This image displays the difference between the boats sailed in the 33rd America's Cup in 2007 and the latest AC72 boats. My take on the Oracle pitchpole is that there was probably a failure somewhere in the foil control system.
With that broken they could not increase the lift on the lee hull enough to keep the windward hull out. Anyway, after certain pitch angle, central lifting-force will not right the boat but, on the contrary, it will contribute to capsize it. If the foil control system was working properly it is my opinion that the boat would never reach that angle. NauticEd is an International Sailing School using advanced interactive eLearning sailing courses. I was watching it on Sunday – the wind was at about 15 knots, yet the boats achieved 43 knots angling downwind and 25 knots angling upwind. Airplanes with an asymmetric wing shape can gain lift with around 5 degrees off the airflow. This was done by observing their tacking and gybing angles and plugging it all into the sine and cosine formulas. I only have a Masters in Engineering – and you can bet a whole pile of dimes that a PhD guy will come back to me on a full explanation.
Watch the wind vectors through the maneuvers and also watch the boat speed increase as it bears away. With limitations on our minds now removed  – you can see that boat speed can just keep on increasing and increasing until the forward component of the force from the wings equals the drag force on the boat. In particular it delves into the calculation of true wind and shows how important true wind direction is when navigating. How to navigate using optimum speeds and how to find your best course to achieve your destination in the fastest time.
You’ll gain the confidence, working knowledge and user experience, through various animations, to fully work a chart plotter device and apply this to your sailing navigation. We have crewed charter boats in the favourite yachting hotspots in the Mediterranean and Caribbean as well as worldwide locations. When they launched their second AC72, the S-shaped boards were replaced by C-shaped boards and the board on starboard has a gentler curve. This reduces drag but not nearly as much as in full foiling with the hull completely out of the water. They have announced that their second AC72 will launch in late May and will be able to foil.
Videos usually show them foiling on the port board, so perhaps the starboard board is better suited to upwind sailing.
I had set up Alinghi's fan club and had become one of the commentators for their VIP guests during racing.
If somebody reads something along the lines of an analysis of the altitude control system on the two boats please post it here.
It would have been sensible to remove the small rig but require the big rig to be able top be split like they have added a panel to the AC45. And if 17 is designed like most multifoilers I am familiar with then the daggerboard supports about 80% of the total weight which means the center of lift of the daggerboard foil is ahead of the boat CG. At the same time, while in a bearaway, a sudden braking caused by the stall and hull landing, can increase pressure on the windward side of the wing. The America's Cup has a long tradition of drastic modifications to fix problems or attempt to speed things up and I think this occasion warrants such development. Now with hydrofoils mounted on the Americas Cup AC72 sailing catamarans, we’re seeing sub 20 degrees off the apparent wind.

Had the drag force equalled the accelerating force before the boat hydrofoiled then the boat would not continue to accelerate.
As the boat gets closer and closer to the apparent wind angle the forward force component reduces.
Now they test different shapes in each hull – so they will be able to test more designs. Even before beginning modifications, they added a winglet to their rudders, visible in the photo below.
They modified a board from their trimaran that won the America’s Cup in 2010 since it would take 3 months to build a new board.
But the most fun was running "The African Queen" - my own VIP spectator boat for South African challenger "Shosholoza." We didn't win all the races but we never lost a party!
I think that they have some sort of push-pull rod connected near the top of the foil trunk and that they can very quickly move the top of the foil fore and aft-as they would have to to be able to reliably fly manually.
The engineering design effort and atmosphere over the past three years must have been intense, ground breaking and so innovative. We observed the true wind speed, the boat speed and the angle off the wind and thus we solved for the remaining. True wind speed matters only in that it helps to get the boat up on the foils but at high boat speeds, by looking at one of the vector diagrams above, an increase in true wind speed will only  marginally help to increase the apparent angle which marginally increases the forward forces.
They put wing sails on the SL33s and modified the daggerboard cases so they could test foils and learn to foil. Its also interesting that hydroptere is much wider then an AC72 yet its rig is much smaller. The mainfoils are incredibly powerful and I'm pretty sure that the pitchpole would have been averted had something not malfunctioned. The biggest revolution has come from the introduction of the wing being able to gain lift from closer angles to the apparent wind AND in a massive reduction in drag. You now have to release your self from the boundaries of old monohull sailing with big hull drag.
Think about drag next time you’re towing a dinghy behind your cruising boat on a close haul. The rudder is the obvious element to trim the platform but that is difficult under the rules. The AC72 has an enormous rig and its not very wide (overall beam) Its a very very overpowered boat and must be handled with the outmost of respect.
But the limiting factor is how much forward force can the winged sail garner out of the wings from the angle between the boat heading and the direction of the apparent wind. The only factors we are now dealing with is drag from the hydrofoils and the force that the wings can eek out of the wind it sees.
This requires an increase in force and the only way then to maintain speed is to bear way – whoops. That angle can never be zero else the boat would be moving straight into wind and that’s not possible under these universal laws. As the apparent wind gets closer and closer to the front of the boat the accelerating force reduces. Once the boat starts pitching, if the CG moves past the daggerboard then the weight of the boat plus the sailing load overturning moment wants to pitchpole the boat. 1) I can't see how the foils can provide a restoring moment, the only chance is using the rudder and I don't see how this can be done, especially since it is now out of the water 2) The bouyancy force (bouyancy is always up) is the only restoring moment in the system.
17 is very slender fwd and as we have seen does not have enough bouyancy in this condition.
From watching videos of many multis PP,ing it seems to me about 45degs is the critical angle. So if the designers figured out the sinkage and CG etc at 45degs the only thing left is the sail drive moment. I believe this is wrong the main has to be pulled in to depower (in a bear away) not eased which increases the pitching moment.

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