On 30 November 2015 Franck Cammas almost lost his right foot when he went overboard and was struck by the horizontal stabilizer on the rudder of his foiling catamaran. The accident ended his hopes of qualifying for the Olympics in Rio. He will be on crutches until late January 2016, when he will begin four to six weeks of rehab. He was in the office working at a stand-up desk with his design less than 10 days after the accident, but it seems clear that he will miss the first America’s Cup World Series event of 2016, in Oman in February.
The Accident and Rescue
The accident occurred during pre-start maneuvers between the two GC32 cats the team uses to prepare for the America’s Cup. Trying to get a better position on the start line against his teammate and sparring partner Adam Minoprio, Cammas made two sharp turns in quick succession and lost his balance. He went overboard near the stern on the port side and suffered a compound fracture of both the tibia and fibula from the impact with the T-shaped rudder. Coach Betrand Pacé gingerly pulled Cammas into the team chase boat, Cammas’s foot attached only by tendons and arteries. Luckily the arteries were not cut, so he suffered relatively little blood loss. Pacé called for emergency medical services and a helicopter to transport Cammas to the university hospital in Nantes. During the 45 minute flight, Cammas continuously tested the feeling in his foot, reassuring himself that there was no serious nerve damage. At the hospital, waking from general anesthesia after two and a half hours of operation, he was relieved to see that he still had his foot. Professor Gouin, the surgeon, had needed plates and screws to reconnect the bones, as the foot had almost been torn off by the impact.
Safety at Speed
Training videos and this accident raise the question of safety precautions for sailing at high speed. There were no serious injuries when Oracle capsized their AC72 in October 2012, the cockpits protecting the crew. With no cockpits in their AC72, Emirates Team New Zealand lost two crew overboard during the Louis Vuitton Cup racing when they stuffed the bows while bearing away at the windward gate. The design rule for the America’s Cup Class catamarans requires cockpits for the crew as part of the safety measures. The AC45 cats being raced in the America’s Cup World Series are dramatically faster since being modified for foiling. The 32 foot long GC32’s have been clocked at over 39 knots. Sitting on top of the hulls of a foiling cat doing 30 knots or more seems like a very risky idea. Let’s hope there are no more serious accidents. Here is a video that shows the danger. It was shot during training on board BAR’s AC45F.
Many large catamarans experience near or full pitch polling incidences. Evidence of this issue is illustrated in many place on the internet particularly U-Tube. Foiling cats are particularly venerable particularly large cats with wing sails.
Listed below are the characteristics that contribute to the likelihood of pitch polling;
• Sea state
• Wind strength
• Height of the sails centre of effort above the boats centre of lateral resistance
• Height of the sails centre of effort above the boats centre of drag
• Height of the boats centre of gravity above the centre of water drag
• Height of the boats centre of gravity above the centre of lateral resistance
• Sail area to mass ratio
• Low pitch inertia
• Low crew weight to boat weight ratio
• Inability of the crew to move aft quickly if need be.
• Lack of resistance to pitch moments
• Low pitch and heave damping, the tendency for pitch and heave motion to be oscillatory
• Determination of the boats crew to maintain maximum possible speed
• Sponsor expectations
• Momentum of the boat at the initiation of the incident
• The ability to bear away at high speed without heeling over
Of these it is bearing away at high speed that is the condition most likely to initiate a pitch pole particularly if the centre of gravity of the boat is significantly above the centre of lateral resistance ( and centre of water drag). A high centre of gravity combined with centrifugal force generated in the turn holds the boat upright resulting in more sail force being able to be generated than if the boat’s track were in a straight line. This situation result is a very quick increase in bow down pitching moment. The most adverse conditions occur when bearing away from a close reach (TWA ~70 Degrees) at high speed to a broad reach (TWA ~110 degrees). The boat is accelerating with the apparent wind and apparent wind angle increasing. Simultaneously the lee way angle is decreasing and dependant on the rate of turn may go negative. The increased drive from the sail (wing) presses the boats bow down and the drop in leeway reduces the foil lift. In less than a second a bow down pitch rate is established that is near impossible to stop. Increasing the angle of attack (AoA) of the main foil will reduce the pitch motion but it will also cause the boat to lift higher out of the water. This sends a mixed message to the guy controlling the foil angle of attack. Initially the bow is pitch bow down “I need more AoA” : “oh the boat is lifting, I need less AoA”. The guy on the helm is busy at this time and another member of the crew should be allocated this task. Then as the boat straightens onto its new course the foil needs to be readjusted accordingly. If the bows hit the water before control is established the sudden increase in drag acting well below the centre of gravity and the boats momentum results in a runaway situation. Bow down pitch rate increases and it is virtually impossible to avoid crashing.
The situation would be much more acceptable if the rudder foils could be used to oppose the bow down pitch rate. The rudder foil would push the stern down and raise the bow, the boat would slightly reduce height increasing the main foil and no mixed signal to the guy controlling the rudder foil AoA. After all this how aeroplanes are flown. The rudder foils are akin to a rudder in the horizontal plane. I believe the rule makers failed to understand the dynamics of these high speed “flying” machines. No one would contemplate restricting rudder movements small changes in angle and expect the crew to steer by changing the AoA of the keel, but that if virtually what has been done.
Seen by Jack Griffin at April 14th, 3:31pm
Thanks for all the info, Alan!
I think you may be mixing up terminology…
The “rudders” (the vertical foil) are indeed like the rudder on an airplane in that they steer the boat, like the rudder on an airplane “steers” the plane. But of course the rudder on an airplane is usually on the trailing edge of the vertical stabilizer.
When you say “rudder foils” I assume you mean the wings on the rudders, or, in aircraft-speak, the “horizontal stabilizers.” You may be thinking of the elevators on the trailing edge of the horizontal stabilizer of an airplane. The AC Class rule forbids elevators on the horizontal stabilizers of the rudder, so, the horizontal stabilizer on the rudder of an AC Class functions more like a “stabilator” on an aircraft – the entire horizontal stabilizer’s angle of incidence is changed, which also changes its angle of attack.
Tom Slingsby explains a little about this, but without all of my pedantic references to terminology. 🙂 in this video.
Nick Holroyd explains it with a diagram in this video.