Yesterday, shortly after noon, we sailed from Vienne. Once a major Roman city, Vienne prospered beside a river that carried goods, people and ideas between inland Gaul and the wider Mediterranean world.

This week, the Rhône carries us and about 100 other guests aboard Riverside Ravel between Lyon and Avignon. We’re on a four-night sampler cruise with Hamburg-based Riverside Luxury Cruises.

After dinner and some very good wine, we strolled up to Ravel’s wheelhouse as the captain guided the ship through Gervans lock, the last lock before Tain-l’Hermitage on our downstream journey along the Rhône.

While he attended to the navigation, we spoke with the engineer. It was a good place to ask a question I suspect many passengers never think much about: What, exactly, is moving this ship?

From the dining room, a river cruise can feel almost effortless. You finish dinner, perhaps linger over a glass of wine, and that evening or the next morning find yourself in another port of call. In the wheelhouse, that same journey becomes a series of practical decisions about power, current and maneuvering a long vessel through narrow locks.

Disclosure: Riverside Luxury Cruises hosted our four-night cruise aboard Riverside Ravel for this review. All opinions are my own.

The Price Of Admission: Two Coffees

Captain Philippe Stypa had a wonderful, understated sense of humor. During the safety briefing on embarkation day, he invited guests to visit the wheelhouse and see how it all worked, adding that there was a cost. That prompted a few questioning looks around the room.

The price, he explained, was two coffees: one for him, black with no sugar or cream, and another for the engineer. It was a welcoming and good-natured way to introduce the ship’s open-bridge policy.

On another visit, as we were leaving Tain-l’Hermitage and heading downstream, I asked to photograph the captain and the engineer. They turned toward me, and I took two or three pictures. The captain then turned back toward the river. “Oh good, we’re still on the river,” he said with a laugh.

That dry delivery made the moment. I appreciated the invitation to see the ship at work and the understated humor of the man in command. The captain and chief engineer made us feel welcome in their workplace.

Electric Motors, Powered By Diesel

The engineer explained that Ravel’s propulsion motors are electric, supplied by generators driven by diesel engines. That arrangement is called diesel-electric propulsion. The motors move the ship, but diesel remains the source of their power. So what’s the advantage?

The advantage is flexibility. The diesel engines do not have to turn the propellers directly; generators supply electricity that can be distributed between propulsion and the ship’s hotel systems. This can allow the generating engines to operate closer to their most efficient load even as demand from the propulsion motors changes. As marine propulsion specialist Wärtsilä explains, that operating flexibility can reduce fuel use compared with running engines inefficiently at low load. The benefit depends on the system and how it is operated; diesel-electric does not automatically mean lower fuel consumption in every situation.

The system dates to Ravel’s construction. A technical company involved in commissioning Crystal Ravel, as the ship was originally named, described work on its electric propulsion and DC electrical network in 2018.

During our conversation, the engineer described six electric motors serving propulsion and maneuvering. He explained that two provided the main propulsion, with the others helping position the bow and stern. Those maneuvering units are called thrusters, and they rotate 360°. Watching the captain work through the lock gave their purpose an immediate context: Moving forward is only part of navigating a river ship.

The River Can Help—Or Hinder

One of the most interesting points concerned the direction of travel. Going downstream, the current was helping us along. The engineer gave us a much higher power figure for traveling upstream. I asked whether that meant almost three times as much power, and he confirmed that it did under the conditions we were discussing.

That comparison described a particular operating situation, rather than a rule that every upstream journey uses three times as much power. Speed, current and operating conditions matter. But it made the river’s influence on the ship much easier to understand.

Passengers tend to think about the river in terms of scenery, ports and water levels. The engineer thinks about the energy required to move through it.

A Floating Hotel Needs Electricity Too

Propulsion is only part of the demand. The ship also has to operate as a hotel: galleys, lighting, refrigeration, ventilation and all the other systems that make life aboard comfortable. In summer, the engineer told us, air conditioning adds a substantial electrical load—particularly during the searing heat of this past summer in France. It is easy to overlook that when you step from a hot Rhône afternoon into a cool lounge. Comfort has an energy requirement of its own, even when the ship is tied up.

A useful distinction helps put these demands into perspective: kilowatts measure power, while kilowatt-hours measure energy used over time. For example, a hypothetical system drawing 100 kilowatts (100 kW) for one hour would consume 100 kilowatt-hours (100 kWh). That distinction matters when comparing the ship’s power demand with the energy a battery could store.

Why Not Solar Panels And Batteries?

Our conversation naturally turned to whether solar panels or batteries could do the job instead or complement it. The engineer’s assessment was that solar alone would not meet this ship’s operating needs, while enough lithium batteries to sustain its full operation would bring significant weight and space demands. His point concerned the practical requirements of Ravel, rather than the prospects for every future river ship.

Solar generation also varies with daylight and weather. Batteries can store energy, but they need to be charged, and their size depends on how much power the vessel needs and how long it must operate between charging opportunities.

Alternating current (AC) and direct current (DC) came up in our discussion, too. I had some familiarity with the subject from my camper van, which has lithium batteries, solar panels, an inverter, a converter and alternator charging. Making those components work together requires a compatible electrical system. Differences between AC and DC are manageable: equipment can convert between them, although the process involves some energy loss, usually as heat. The U.S. Department of Energy explains, for example, how inverters turn the direct current produced by solar panels into alternating current.

It is also worth being precise about “hybrid.” Diesel-electric describes how Ravel’s diesel engines generate electricity to power its propulsion motors. Whether a vessel also uses batteries for propulsion is a separate question. Electric motors alone do not make a ship battery-powered: they can run on electricity supplied by generators, without batteries supplying their power.

The Ship Once Needed A Ship Of Its Own

Ravel’s engineering story has another chapter that we reported before she began sailing here. In our 2023 article, How Riverside Ravel Got To The Rhone, we described how the vessel, which had previously operated on the Danube, was laid up in Rotterdam following Crystal’s financial collapse in 2022. There, she was loaded aboard the transport ship Yacht Servant for a journey to Fos-sur-Mer on France’s Mediterranean coast.

Ravel arrived in her new cruising region aboard another ship. Our earlier story includes a photograph of that remarkable journey—a reminder that repositioning a river ship can be a major operation in its own right.

Back Through The Lock

As we talked in the wheelhouse that night, the captain continued attending to the passage. Then the lock gates opened, and Ravel made her way out toward our next stop.

We had come upstairs after a very good dinner and found another absorbing part of the cruise. Below us was the floating hotel we had been enjoying. Around us were the controls, equipment and people responsible for taking it down the Rhône. As we returned to our cozy stateroom, I had a new appreciation for the work behind a journey that, from the dining room, had seemed so effortless.