Under sail, autonomy is at hand

Nautor Swan is one of sailing’s icon shipyards. Since its opening in 1966, its boats have made history for elegance, performance, build quality and reliability.

More than 2,350 boats have been built, with lengths ranging from 10 to 40 metres and models ranging from cruisers and blue water yachts to pure racers.

Among the yard’s latest launches is the Swan 88 DreamCatcher, a maxi sailing yacht designed for cruising and the first Swan to feature a diesel-electric solution expressly requested by its owner. The on-board propulsion and energy management system was developed with Torqeedo, a pioneer and market leader in electric mobility on water (operating since 2005, Torqeedo produces electric and hybrid systems from 0.5 to 200 kW for commercial and leisure applications). The system therefore manages both propulsion, which although on a sailing boat does not seem to be the priority, is nevertheless a key factor during navigation, manoeuvring and in terms of safety, and the power supply of the various on-board consumers. The Swan 88 DreamCatcher is a maxi-yacht 28.27 metres long, weighing 54,100 kilos; it is a yacht with a series of systems that require a lot of energy (just think of the professional kitchen with ovens, fridge, freezer, induction burners, the air conditioning system, the on-board hydraulic systems used to adjust sails and manoeuvres, the infotainment and navigation systems, etc.).

Sailing at 8 knots, the yacht is energetically self-sufficient

The Swan 88 DreamCatcher is the result of three years of collaboration between Nautor Swan and Torqeedo Customized Solutions business unit. The yacht features an optimised version of Torqeedo‘s Deep Blue system consisting of a custom-developed 120 kW electric drive system with direct drive, two 45 kW generators and 160 kWh of energy storage. An additional 50 kW electric motor keeps the on-board hydraulic systems pressurised. It is a system that allows the yacht to reach a maximum speed of 11.4 knots when powered by the engine and achieve energy independence when sailing in good conditions, thanks to the use of the hydrogenerator.

A few days after the launch of DreamCatcher, a second Swan 88 equipped with a 230 hp endothermic engine was put in the water. The two boats recorded the same top speeds, and even in terms of cruising range and the litres of diesel taken into the tanks, the hybrid-electric and endothermic versions are very similar. What is different is the weight, with an increase of around 1.5 tonnes for the hybrid-electric version.

An important factor for the system is the propeller, the 120 kW Deep Blue inboard motor, developed for the Swan 88, drives the yacht’s controllable-pitch propeller. This propeller is a significant advantage for an electric drivetrain, as its pitch and performance characteristics can be changed at the push of a button. This feature allows for a seamless transition between sailing and motoring modes. Under power, the system delivers high torque and thrust and is optimised for efficiency. While sailing, the system minimises drag for optimal sailing speed and performance or can be optimised for maximum renewable energy production. In hydrogeneration mode, Deep Blue’s advanced algorithms continuously monitor and adjust performance several times per second, providing renewable energy production, the speed loss due to use of the hydrogenerator is small, around 1.0 knot when the boat is fully powered up by the sails.  

At around 8 knots of sailing speed the Deep Blue system makes the boat independent by generating sufficient energy for all on-board systems. Given that a yacht like DreamCatcher can reach 8 knots even with light wind, it is capable, for example, of crossing the Atlantic while keeping its batteries fully charged without needing to start the generators.

The high-capacity battery bank consists of four Deep Blue Battery 40 totalling 160 kWh; these are prismatic cell LiNMC batteries that Torqeedo developed with BMW. It powers the zero-emission propulsion system, and a 50 kW Deep Blue motor that keeps the yacht’s hydraulic systems pressurised, including the bow and stern thrusters, windlass, and winches. DC/DC converters ensure the yacht’s 24-volt electrical system and electronics are always online. Amenities that require a lot of power, such as the air conditioning, oven, watermaker, dishwasher, and washing machine, are also integrated into the Deep Blue energy management infrastructure courtesy of a 22 kW DC/AC inverter. These amenities provide the utmost comfort and convenience, while the Deep Blue system ensures their power consumption is efficiently monitored and managed

Deep Blue is a holistic system that not only generates its own green power while sailing, it also manages, balances, and delivers energy to all of the yacht’s onboard systems. Developed with the aim of simplifying its use, all controls are integrated into the yacht’s multifunctional displays, thanks to a joint development between Torqeedo, Nautor Swan and Navico (among the reference players in the supply of integrated systems and products for energy management, digital control and monitoring, networked devices and marine electronics).

Autonomy and recharging

Aside from the yacht’s complete self-sufficiency when sailing with the hydrogenerator in operation, as mentioned above, its range still reaches four-digit figures.

According to data collected by the yard, DreamCatcher in motoring mode with generator running and a speed of 10 knots achieves 1,000 nautical miles of autonomy and dropping the speed to 7.5 knots the autonomy rises to 2,000 which, to return to the example above, corresponds to half the Atlantic crossing.

In 100% electric mode DreamCatcher sails for about 1.5 hours at 10 knots and 5 hours at 7 knots. Once at anchor the yacht, with the electric utilities for hotel services running, can stay about 12 hours without having to switch on the two 45 kW generators that recharge the high-capacity battery bank on board in about 1.5 hours.

For shore charging, the integrated 22 kW onboard charger brings the batteries to 100% in six hours.

The noise when the generators are running is extremely low. Depending on whether one or two generators are running, the yard points out, the noise levels recorded are around half or even ¼ of the corresponding endothermic boat.

(by Paola Bertelli)