MODX: An electric 70ft catamaran with inflatable wingsails!

The MODX is a 70ft catamaran with fully automated twin inflatable rotating wingsails set on telescopic retractable masts and powered by electric motors with variable pitch, hydrogenerating propellers.

Every now and again something really different comes along, and this was one of those concepts you don’t think will come to reality. I say that, having spoken to the design team about it years ago, and seen plenty of renderings of what it might look like.

So, the curiosity of such a venture we expected. The fact that our video tour from its launch at the International Multihull Show in May was one of our fastest to reach 100,000 views, less so. Also noteworthy with that video is the sheer amount of largely positive comments supporting the technological development (when you consider that these comments stem from a typically sceptical audience).

Everything about this project is quite fascinating, from the VPLP-designed wave-piercing hulls to the automated power and sail systems. A primary goal for the MODX is to offer zero CO2 emission cruising by utilising completely renewable energies.

The scheme carries plenty of credibility, thanks to design by VPLP and construction by Océan Développement, the yard responsible for the fleet of MOD 70 ocean racing one-design trimarans built in 2008.

However, it’s those enormous wingsails which spike the most interest, of course.

Built by Aeroforce, a company set up specifically to develop the technology, these twin AF125s are each 125m2 inflatable wings with auto trim functionality. They’re claimed to be 1.7 times more efficient, safer (no winches/ropes), and create 20% more space aboard than conventional rigs.

Blow up sails

“Powerful and stable wings that can be automated is why we developed Aeroforce,” CEO Jean Guyon told me during the yacht’s premiere in La Grande Motte. “The MODX’s goal was to be energy independent. So we needed a fast boat, but it’s also why there are wingsails – the target was that in 10 knots wind, we should do 10 knots boat speed.”

The telescopic masts are formed of six sections which rotate around bearings at waterline and deck level. The masts are 23m high when fully raised and have a deep reef to reduce the sailplan to 65%. (It’s worth noting that most sailing footage so far shows the yacht in reefed format.)

The wings are housed in huge cradles above the coachroof and take eight minutes to hoist and inflate. Made from thermoplastic polyurethane (TPU), these sails are inflated to a comparatively low pressure of 100 millibar, or around 10 times less pressure than a typical inflatable paddleboard – which allows pumps to be used for inflation rather than compressors.

The wings also have a trailing flap, which works like those of an aeroplane to increase lift by 30-40%, Guyon estimates. He explained how the airfoil shape increases airflow on both sides of the wing, “so pointing is quite good at 40-45° to the apparent wind.”

In terms of performance, the MODX has hit 21.5 knots in 25 knots of wind at 150° to the apparent, or 9.5 knots in 11.5 knots at 46° apparent – which is already very close to the initial target of 10 knots in 10 knots of wind.

The gearbox and rotating chain used at the mast bases allow for 360° rotation of the wings, providing a tangible benefit for spilling wind. Consider how smooth and quiet gybes can be when you can completely open the sails and rotate the masts downwind through the gybe. This brings us to the yacht’s impressive automatic operation.

Auto functionality

The MODX is piloted from a single wheel and internal helm station, adorned with touchscreens. “The project is trying to attract people from power without the complexity of sail,” is how VPLP’s Mathius Maurios explained the concept to me.
“It’s about being on the water without being stressed.” With this in mind, the project team wanted a fully automated sail/wing control system, as easy to use as cruise control.

They worked with Madintec to develop a highly sophisticated yet approachable wing, hydro and energy management system.

This French company has developed performance autopilot systems for many of the top IMOCA 60 teams. So when you look at the helm station on the yacht, on one side is the throttle control for the electric engine, and on the other, a more crude, simple throttle lever (which looks like something out of a Thunderbirds rocket).

So, in terms of piloting this 70ft performance catamaran, once wings are raised, the operator simply pushes the wing throttle lever forward, selecting from 0-100% of potential force. Therefore, it’s not just an auto-driving boat, but one that uses auto-tuned sails too. If you only want 50% of the power available, it’ll release the sails to spill more wind.

Silent sailing, silent power

With no running rigging, the coachroof can be pushed out to maximum beam, creating the largest area possible for solar panels. The MODX has 70m2 of panels, which provide a peak of 15kW, or up to 35% of its electrical energy mix. Although the company is looking into a flybridge alternative to cater to demand, this wide, flat surface on the first boat is also ideal for harvesting rainwater, and there are two 400lt tanks dedicated to this.

At the heart of the electrical system is a 250kWh LFP lithium battery bank – as a comparison a battery in a large electric car is around 90kWh. It’s enough for guests to live aboard for 10 days without sun, wind or engine use, or provides 110 miles motoring range at 5 knots. When sailing, the variable pitch propeller can hydrogenerate power back into the battery bank. So, at 15 knots boat speed, it’s possible to generate 16kWh back into the system.

Unfortunately, what we can’t show you is the nucleus of the MODX system: its technical rooms. I was granted a quick look but not allowed to take photos or video. These are located at the mast bases at the foot of each forward companionway and house the electrical and telescopic mast systems, in a cocoon of carbon fibre with significant bulkheads to help support the latter. Otherwise, the MODX is built in glassfibre, using bio-sourced resin and 40% recycled foam.

The rest of the interior in the first boat is suitably luxurious, particularly on the main deck, which offers motoryacht-style comfort, near-surround ocean views, and 135m2 living space in the saloon, fore and aft decks. However, we can’t go into more accommodation detail as it’s a largely customisable space to suit private, charter or ‘expedition’ use.

A MOD Future?

So what is the future for this concept, and what size vessels might the Aeroforce wings be practical for? “The initial design was for 55ft, but we needed more solar to reach the efficiency targets,” Guyon explained. The right balance of solar and boat speed was found at 70ft. He added that doing a 100-footer would be easier than a 55: “I don’t see the potential in less than a 100m2 wingsail size.”

Aeroforce is also looking at the obvious potential of its wings for commercial shipping, as well as for leisure monohulls, where they might provide less heeling moment and more thrust.

MODX specifications

LOA: 21.33m / 70ft 0in
Beam: 10.00m / 32ft 10in
Draught: 2.00m / 6ft 7in
Air draught: 4.60m / 15ft 1in
Wing area: 2 x 125m2 / 2 x 1,345ft2
Displacement: 30,000kg / 66,138lb
Electric motors: 2 x 20kW / 2 x 27hp

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