The problem for Vestas Sailrocket was that at over 50 knots small bubbles begin to form around the hydrofoil that sits underneath the boat to keep it balanced. This effect, known ascavitation, drastically increases the drag and meant that the team struggled to get much beyond 50 knots. The team spent 2012 designing and analysing new hydrofoils, but still experienced the same 50 knot limit: there seemed no way past this "bubble barrier". Last week, they finally found the answer by adding small perpendicular "fences" at several positions along the hydrofoil, which seemed to solve the problem.