A British team of rocket scientists reveal their answer to safe foiling offshore
As America’s Cup Defender Oracle regroups and rebuilds after a spectacular and catastrophic pitchpole, a small team of rocket scientists on this side of the Atlantic is continuing to develop a very different hydrofoil configuration aimed specifically at resolving the problems of foils in waves.
The C-Fly project uses an innovative foil configuration that it’s designers claim makes it impossible to pitch pole.
I went to Weymouth to sail her and the cat is our Boat of the Month feature in the current Dec issue of YW.
This short video was shot and edited by the team as we sailed in Portland harbour and Weymouth Bay. The breeze was 14-16 knots, sufficient to see us sitting steady at 22-23 knots in the flat water inside the harbour.
Outside the harbour the south easterly wind direction was blowing into Weymouth Bay making the sea state more of a challenge.
YW Dec 2012 Issue for the full feature on what makes this innovative foiling configuration so stable in waves and why this could be the next step for hydrofoiling offshore.
YW feature excerpt:
The use of four foils is certainly an unusual configuration. Most surface piercing foilers are arranged in a triangular arrangement where the main foils are forward and the aft foil acts like the tail plane on an aircraft, balancing the boat fore and aft as well as resisting any forward pitching force caused by the rig. The trouble is that if this aft foil lifts out of the water, the stern is no longer held down and the boat can pitch pole. Which is precisely what happened to the French team in 2009.
“Our configuration means that the boat is supported in each corner,” he continued. “The further the bows are pressed down, the more foils are immersed and the greater the lift they produce. In fact each foil can exert a maximum of 1.5 tonnes of vertical force at a speed of 40 knots on a boat that weighs around 500kg.”
But this is just the start.
“One of the problems with any high speed foil is that of cavitation,” explained Richard Varvill. “When a wetted section starts to cavitate you lose control. With the extreme pitching and high angles of attack as the foil hits and breaks clear of the water through waves, we knew we had to design a ventilated foil so that the foil worked without being in direct contact with the water as wetted sections are.”
Of the 20,000 man hours that has gone into developing this cat the team spent a considerable amount of time in a high speed test tank where they developed the superventilating foils. The most noticeable feature here is that the forward foil surfaces are stepped which helps to draw down air from the surface at key areas to keep the foil ventilated.
But there is a further twist to these innovative foils, literally. The forward foils also rotate to form the steering arrangement for the cat at speed. Connected to conventional looking tillers aft, the configuration is to sailing what a rear wheel steered dumper truck is to a car, especially at low speed where you have to tune into a different motion when tacking. In full flight however, you would be hard pressed to tell the difference between this and a conventional arrangement.
Another significant feature of the C-FLY configuration is that there are no moving parts on any of the four foils to adjust trim or ride height. The entire system is self balancing, something that the team believes is essential for long distance offshore foils. In light winds all four foils can be lifted clear of the water to allow the cat to sail in a conventional displacement mode, another advantage an indeed requirement for maintaining a good average speed offshore.
Underway and in 14-16 knots of breeze with flat water inside Portland Harbour she felt sure footed. With a reef in the mainsail C-Fly rose onto her foils with ease and accelerated to a steady 22-23knots. As gusts swept across the harbour her leeward bow dipped with each puff but never felt precarious as she added a knot or two to her speed. Indeed, she seemed to revel in beam reaching, an angle that would normally cause high performance cats problems.
But the bigger test was outside in Weymouth Bay where the waves were running at around 1m and the breeze was up. Once again she appeared to do exactly what the designers had said, riding the waves with far more confidence than her guest/journalist crew member who couldn’t resist the natural reaction to crack sheets each time she felt pressed.
Taking the helm for a few runs back inside the harbour it was clear that there are still a few bugs to iron out, the most noticeable being the vibration sent back through to the tillers. Having recently conducted some underwater video analysis of the forward foils at speed the team is convinced it can now rectify the issue. She’s pretty wet as well, especially if you’re the forward most crew member where the force of the jet of spray from her front windward foil provides a hint of the forces that are involved to provide a stable cat platform. But overall she was stable and easy to get on with quickly.