LIVE #1 Electric propulsion

Following topics debated, we realized that electric propulsion was one of the subjects that generated the most discussion on the Excess Lab. In addition, these days we get a lot of requests for hybrid or electric propulsion boats. However, questions arise in terms of speed, range and additional costs.

Therefore we organized a ‘LIVE’ discussion earlier in the year with several members of the Excess Lab who were interested in the subject.

We wanted to share the main topics raised during this 'LIVE' event with you.

“With the Excess 15 prototype, the E'Lab, equipped with diesel-electric hybrid propulsion, we’ve succeeded in creating a system that is easy to use, works well and has shown itself to be very reliable,” explains Hervé Piveteau.

If we can manage to offer a 100% electric or a hybrid propulsion system on an Excess, we’re willing to bet that lots of boaters will be interested and in turn, that we’ll be able to lower the cost price of the option. As Excess is a builder of production catamarans, we need a minimum 20% take-up rate (proportion of buyers) in order to be able to offer these options.

The discussion with the Excess Lab members kicked off after Hervé presented the participants with four hybrid configurations under consideration for an Excess 11.

Each of the four options considered takes into account four variables: Boatspeed, 100% electric propulsion time, additional weight and cost.

We went on to talk about E'Lab, our Excess 15 that’s equipped with the Torqeedo hybrid propulsion system, because through the tests that have been carried out with this boat, we’ve been able to draw some interesting conclusions, notably in terms of power.

For a smaller catamaran, the size of an Excess 11, we know that you need about 10 kW of power to cruise at 6 knots, but that if you want to make 7 knots, you’ll need almost double that amount of electricity. And using the boat's resistance curves, we can see that we need to multiply the electrical power by four to make 8 knots. “I think this is something very important to keep in mind,” says Hervé.

Note also that these calculations are digital and theoretical. None of this takes into account wind, sea state or hull cleanliness. When you decide what power you’re using, you’ve therefore got to factor in a higher margin, because the external elements will clearly affect propulsion efficiency!

“Often at sea, you have to motor into a strong wind and maintain a high power level or conversely, you might be under sail, in light airs, but have a strong counter current. In such situations, I would need to be able to count on a speed of more than 6 knots” admitted one owner. “And I think a weight of 350 kilos [770 lb] for the electric motor is too much” he commented, referring to the first hypothesis the Hervé presented: 2 hours with 100% electric propulsion, at a speed of 6.5 knots, an option price of € 77,000 and additional weight of 338kg.

Another member recognized that it’s probably necessary “to wait longer before we see a reduction in weight and a decrease in prices for the solutions that involve electric propulsion”. The technology, as much in terms of motors as of batteries, progresses regularly.

One Excess Lab member asked about the current status of a hybrid option for other Excess models. “We decided to study an installation for the Excess 11, but that doesn't mean we're ruling out the option for the Excess 12, the Excess 14 or the Excess 15. It seems that the 11 offers a good compromise in terms of speed, range and cost,” says Hervé. “We’d like to try and achieve performance close to that of a diesel engine by seeking ‘unlimited’ range at 6.5 knots. When we talk about unlimited range, we mean the cruising speed that the hybrid electric drivetrain, supported by a generator, will allow you to reach without discharging the batteries. The generator will cover your propulsion needs for long periods.

“We need 2 hours of self-sufficiency in ‘all-electric’ mode to be able to leave the port and return in silence. That's a typical day's cruising for us when there’s enough wind to sail,” added one participant.

“We could also opt for a twin drivetrain system, i.e. a diesel engine in one hull and an electric motor in the other,” suggested another Lab member. We could even see a wider offer when it comes to energy, including additional solar panels, wind generators or an even more advanced management interface, in the style of what already exists in the automotive world …

We ended the discussion by concluding that there are real expectations from the members of the Lab that were present during the LIVE event on electric propulsion. We have to continue digging into this subject in order to satisfy this need. “I would like to buy a brand-new catamaran that offers durability, reliability and cutting edge technologies. And there are many customers like me” mentioned one participant. And we agree. This is why we’re committed to continue studying this subject.

It was a pleasure to exchange with our members on electric propulsion. Now, we’d like to invite you to participate and give us your input. Let’s continue the discussion here on this topic! What are your expectations on the propulsion of our future Excess catamarans