A load sensor on the windward shroud is something I've advocated in response to Tom Speer with reference to the windward foil deployment rule. Perhaps the sensor could release something other than the shroud ...?
Steve, you're suggesting the crew should have powered up the wing to lift the windward hull, while I'm suggesting they should have dumped pressure from the upper section. Do we need to talk this out, or do we just agree that the way these boats are currently set up "transition" is a sensitive time? Is a design change called for to make it less sensitive?
[note: If a RULE change is called for and it's too late to change the rule for America's Cup 34, the discussion can be had at
http://www.boatdesign.net/forums/sailboats/next-2016-so-americas-cup-ac-35-a-44996.html.]
Hi Stephen,
What I said was that the transition from not sailing at full speed to the bearaway may have contributed to the pitchpole. Transition from sailing upwind to bearing off around a mark on catamarans is always a sensitive time. If they had taken enough time to get up to speed, the boat should have been fully foiling before the bearaway began. On a catamaran the faster you are sailing when approaching a bearaway the safer it becomes, as you are then sailing into apparent wind and the tendency for the bows to go down decreases. When you power up from a standstill and try to do a bearaway immediately you haven't given the boat enough time to develop the apparent wind which gives you the safety margin. What I see in the video is that the boat only starts foiling mid-way into the bearaway, as the boat accelerates the windward hull falls in the water adding drag, with the rig powered up. So I think they made the error of trying a bearaway in rough conditions without setting themselves up to succeed at the manouvre first. So I think that part of the accident can be attributed to operator error, although I have huge respect for the sailors involved.
I do believe that the boat design was flawed in that if they had designed it to twist on purpose as some believe, it sounded like a really good concept that had too many variables, and they may have produced a boat more suited to flat water moderate wind sailing than what they sent it out in. In our language we say 'slim vang sy baas' which is not easy to translate, but basically means that a clever person is his own undoing. So if the engineers designed the twist into the platform, it was a great concept that couldn't be properly controlled, and if the twist was not intentionally designed into the platform, then it is as a result of trying to reduce weight to the point where they have sacrificed platform stiffness. Either way, I think they goofed. Most catsailors will agree that platform stiffness is critical, to the point where A-class sailors glue their beams into the hulls as a bolted connection allows some flex.
I don't think any rule changes are needed - we don't know what type of foiling height control TNZ is using, and some are speculating that OR17 were using manual foil AoA control, perhaps that was their undoing. The rules basically made it impossible to design foiling multi's, and TNZ's engineers acchieved the impossible, perhaps OR have to rethink their strategy.
My statement about NOT dumping the mainsail when the bows go down, is that if on a beam reach or deeper, you do this, you will power up the wing, not depower it. The way to stall any wing is to increase it's AoA, ie sheet it in. A stalled wing produces very little lift but still gives a lot of aero drag, so I'm not saying they would have saved it, but I know from experience that when the bows go down you sheet in the spinnaker & main and bear away as hard as you can. We have saved the boat this way many times when the rudders are clear out of the water and the boom-mast gooseneck is underwater ! The time to ease the main would have been while going into the bearaway, which they did not do. This would have been wise especially since they did not have the kite up.
If you are not a catsailor, none of what I just wrote will make any sense as it's completely contradictory to how you would think as a monohull sailor.
