Sunreef Yachts has presented a wing sail that can rotate through 360 degrees, change its shape under way and raise or lower itself without crew handling. Announced on 10 November, the Sunreef Wing is intended for the builder’s next generation of sailing catamarans. For a cruising crew, the first question is how much work it could take out of setting and trimming sail over a long passage.
How the Sunreef Wing sail works
The wing is self-supporting and turns to suit the apparent wind, the wind felt on board as the boat moves. Sunreef says the system also adjusts the wing’s camber, the curvature of its profile, as conditions change. The yard says it can raise the wing at anchor even with the wind coming from astern, a useful proposition on a boat that may lie differently to wind and current.
Sunreef describes an AI-assisted control system that reads sailing conditions and coordinates the wing, rudders and propulsion. It also lists voice commands among the controls. For a crew, the immediate appeal is fewer routine trips to handle sails. The announcement leaves several practical questions open, including what the crew can operate manually after a power loss and how quickly the wing can be depowered or lowered in a squall.
What the performance figures tell us
Sunreef claims 50% more lift and 40% more propulsive force than a conventional sail of the same area in optimal apparent-wind conditions. Lift is the aerodynamic force perpendicular to the apparent wind. The forward component of the total aerodynamic force drives the boat. A gain in drive under one set of conditions gives no direct estimate of boat speed, which also depends on hull resistance, sea state and the boat’s heading.
The release gives no comparative test protocol or independently measured speed or upwind data. A useful sea trial would show the range of wind angles and speeds over which the figures hold, as well as how the rig behaves as the wind builds and the boat starts pitching.
What remains open for cruising crews
Sunreef says the wing can also harvest energy from apparent wind while motoring. The yard plans to manage it alongside the engines, hydrogeneration and its Solar Skin panels. The useful number here would be the net energy balance at a stated boat speed and in stated wind conditions, after accounting for any extra propulsion needed to overcome the drag of harvesting energy.
Sunreef intends to bring the wing across its sailing range. Its announcement gives neither a first production model nor an availability date. Until there are sea-trial results, the practical proposition for owners is automated sail handling, with the gains in speed, upwind progress and net energy still to be measured.
More from the builder: Sunreef Yachts.