Nikola Tesla’s dream of transmitting electricity through the air without a single cable spent over a century waiting for its moment. The Serbian-born inventor devoted a large part of his career to attempting wireless power transmission over any terrestrial distance without energy loss. This ambition took shape in the Wardenclyffe Tower, a bold project that was ultimately never completed.

Yet that vision did not die with him. It survived in miniature, tucked inside the charging pads where we leave our mobile phones every night. Over time, it expanded—first to electric cars and buses, and now to a location where Tesla never imagined wireless power would be needed: out on the open ocean, miles away from any power grid.

The adoption of electric propulsion across marine vessels—ranging from small pleasure craft to ferries and Service Operation Vessels (SOVs)—has driven engineering teams to pursue a shared goal: wireless inductive charging. Early prototypes demonstrate that this technology can now top up vessel batteries both at berth and out at sea.

A project launched in 2017 by Finnish marine tech company Wärtsilä, in partnership with ferry operator Norled aboard the MF Folgefonn in Norway, marked the first commercial-scale trial of inductive charging in the maritime industry.

The system used large magnetic plates embedded in both the vessel’s hull and the port berth, transferring power across a gap of up to 50 centimetres without physical contact.

Paired with an automated mooring system, charging initiates less than a minute after docking, delivering over one megawatt of power at high efficiency. This pioneer project proved that removing physical cables in marine environments is entirely viable, eliminating long-standing issues with mechanical wear and saltwater corrosion.

However, engineers are pushing those limits even further. That is the goal of the Ocean Charger project, led by Norwegian shipbuilder Vard and SINTEF, one of Europe’s leading independent research organisations. 

“We have looked at a lot of solutions here,” adds Giuseppe Guidi, Senior Research Scientist at SINTEF. “And we have tested a possible solution that works almost like a regular electrical contact. But we can avoid all the problems because we transfer power inductively, encapsulating the plug itself in materials that can withstand just about anything”.

Beyond chemical exposure, ship motion presents a major challenge. Waves, wind, and tides keep vessels in constant movement, making it virtually impossible to hold them completely still alongside a pier. That swaying strains plastic and metal cables, risking bent plugs, loose fittings, or sudden power disconnections mid-charge—a potential hazard that engineers at Vard and SINTEF set out to solve with wireless charging.

The design relies on waterproof inductive charging coils installed on both the vessel and the charging station—a modern evolution of Tesla’s original concept. These coils transfer current across a substantial distance via a magnetic field without physical contact. It is “almost like putting a cup in a cup holder,” notes Guidi, describing a plug-and-play system that eliminates the need for precise alignment when lowering the plug into the receiver.

To handle such massive currents safely at sea, engineers at Vard and SINTEF designed custom heavy-duty cabling and electromagnetic components shielded against physical wear and extreme salt-water corrosion. They also developed control software capable of monitoring electricity flow in real time to minimise power loss.

While the validation prototype used for testing is compact enough to carry with one hand, the full-scale version will be three times larger and fifty times heavier, capable of delivering up to 5 MW in the middle of the ocean. Even at that scale, it remains a far more cost-effective and eco-friendly option for powering wind farm support fleets.

“The genius of recharging at sea in this way lies in the fact that locally produced electrical energy is used directly to recharge the ships, ensuring that very little energy is wasted,” says Vollset Lien.

The research team has also planned for low-wind conditions when turbines do not generate enough electricity to recharge vessels. For those scenarios, Vard proposes using Offshore Substations (OSS)—structures traditionally used to collect electricity from giant wind turbines and send it inland.

Thanks to inductive wireless charging, these substations are on the verge of becoming the floating charging stations of the future. By taking advantage of their location at the heart of offshore wind farms, maintenance vessels can recharge their batteries directly at the original source in the middle of the Atlantic or the North Sea, eliminating long and costly return journeys to the coast just to refuel.

Combining an OSS with wireless technology resolves the major logistical and safety challenges presented by the maritime environment. By integrating electromagnetic transmission systems directly into the substation or into connected buoys, the recharging process is managed in a fully automated manner via software, without the crew having to handle heavy high-voltage connectors on slippery decks in rough seas.

Furthermore, these substations can incorporate their own intermediate storage systems to accumulate energy, maintaining a constant, cable-free power supply for service ships even on days when the wind has stopped blowing.

With projects like Ocean Charger advancing towards their commercial rollout, the challenge is no longer proving that the technology works, but establishing it as a standard feature across electric vessels. Once adopted, refuelling on the high seas will cease to be an engineering feat and will become a task as simple as placing a mobile phone on a wireless charging pad.

Sources:

• Wärtsilä
• SINTEF
• Vard
• Science direct