I drove a rare solar-electric yacht to test propulsion in clean sea, here’s how it went

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While we at Electrek often tend to focus on electric vehicles taking over the roads, it’s important to remember that our inevitable abandonment of fossil fuels stems from all modes of transportation, whether by land, air or even sea. I recently had the opportunity to board the Sunwater Marine Ramblin ‘Rose, a 40-foot sailboat powered by solar panels and electric propulsion. It is one of the only ships of its kind on the west coast.

Sunwater Marine is a San Diego-based nautical transportation company focused on bringing the benefits of renewable energy and electric propulsion to the people of the sea.

It was founded by President James Richmond in 2020, amid the global pandemic. Richmond had a little more free time to search for an offshore cruise ship that he could add solar power to.

James has been sailing for over 50 years and has nearly 40 years of experience in the renewable energy and energy efficiency industry.

My faithful captain, James Richmond, founder and president of Sunwater Marine

He quickly found a 2015 Leopard 40 catamaran and had initially planned to simply add solar panels for an electric cooker and energy-efficient watermaker.

However, James quickly discovered viable options for electric propulsion and began to research the possibility of converting his new yacht to solar power.

The result is the Ramblin ‘Rose, a catamaran that can carry 12 passengers and sleep up to nine. It also happens to be one of the only solar electric yachts on the West Coast.

I had the chance to take the solar-electric yacht out of the beautiful Coronado and test the technology myself.

Ramblin ‘Rose solar electric yacht

As previously mentioned, Sunwater Marine’s Ramblin ‘Rose is centered around a Leopard 40 catamaran, built by Robertson & Caine in South Africa. Richmond then invested an additional $ 100,000 in a renewable energy conversion, equipping the yacht with solar panels and electric motors.

While the original catamaran came with traditional solar panels, Richmond’s experience in renewables told him that this would not be enough for his solar-electric yacht.

It added lighter and more flexible solar technology from Sunflare, the first company to successfully mass-produce thin and durable CIGS (copper indium gallium selenide) solar panels.

Sunflare signs on the Ramblin ‘Rose work individually with their own bypass diode, so if one is shaded (by the sail for example), the others still work.

Richmond has also separated the solar panels into three distinct areas, so if one side of the boat is shaded, the other two are still harnessing solar power in the boat’s batteries.

He also showed me how durable these advanced solar panels are, as I could walk on them without worrying about breaking glass or damaging them.

The panels help to charge the batteries of the electric yacht while sailing and tell the captain when they are doing so.

Electric propulsion and battery packs

To help this vessel get in and out of the marina and out to sea, the President of Sunwater Marine researched electric propulsion systems around the world and decided OCEANVOLT was the best option.

The solar-electric yacht now features dual 15kW ServoProp OCEANVOLT sail drives, using unique propeller blades that can change pitch to optimize efficiency and even regenerate power.

The software-controlled variable system automatically adjusts the pitch of each of the propeller blades, so that power generation and output are always optimal. It is much more efficient than traditional fixed propellers.

The electric propulsion is powered by a 48 volt system, which means it is safe to touch without an electric shock (an ideal situation for fun at sea).

Each yacht’s electric motor is powered by a bank of 12 lithium iron phosphate (LFP) batteries on each side, 24 in total. The batteries provide 21 kWh of power on each side of the vessel, 42 kWh in total.

Richmond explained that he also placed each battery pack eight inches from the bottom of the boat, so if water were to enter the batteries would still be fine. In addition, the captain showed me a backup storage for eight additional batteries in case something went wrong at sea.

The status of each battery is monitored 24/7 by a Battery Management Supervision System (BMS) which will shut down the battery bank if an individual battery begins to malfunction. Fire is not something you want on a boat, although it is surrounded by water.

Additionally, the system was implemented to safely operate minimum electrical functions under all conditions, so if the electric yacht were to tip over, there would still be current to send a distress signal.

Thoughts on the future of electric propulsion

After holding the helm of the Ramblin ‘Rose, there is much to be excited about the future of electric propulsion at sea, especially on a magnificent yacht.

The ride itself was eerily smooth and quiet compared to the diesel engines, with no vibration throughout the boat. If you haven’t looked back and seen the wake of the electric motors, you might not even notice the yacht was propelled.

There is a lot of potential in electric propulsion, especially when it comes to propellers that can change their angle from a distance like the OCEANVOLT ServoProps. This makes reversing the electric yacht in particular much easier for captains compared to fixed propellers designed to move forward.

The ability to set sail and regenerate propeller power is also a huge plus and pairs well with advanced solar panels. Plus, you always have shore power as a backup when you’re in a rush.

From what I have seen, the biggest hurdle going forward will be battery capacity and the provision of sufficient stored energy to power the yacht’s electric propulsion systems.

Solar panels help a lot, but it’s a relatively slow process. Smaller, lighter battery options will one day be crucial for longer distances at higher speeds at sea. Until then, we still have sun and wind to take over.

Currently, range and top speed are still limited by this lack of excess energy below deck. We did not take the Ramblin ‘Rose above 7.5 knots (~ 8.6 mph) because we didn’t want to burn off all of our battery life (that was also relative to the charter that sailed after us that day).

The solar-electric yacht still has diesel engines on board for emergencies, but the founder of Sunwater Marine has agreed with me that we would like to see a day when these engines are no longer needed at all. Unfortunately, the technology is not there yet.

Fortunately, people like Richmond and Sunwater Marine are using their knowledge and resources (and personal funds) to figure these things out for the masses, while also spreading the word about electric propulsion. It has become a truly viable option at sea, although for the moment it is only the support of other forms of propulsion such as sailing.

If you ever visit the San Diego area, I highly recommend that you contact Sunwater Marine and charter the Ramblin ‘Rose, or one of the other solar electric yachts that Captain Richmond works on.

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