Story and photos by Keith Dickey and Rebecca Frontz
Planning an Atlantic crossing with an electric motor presents unique challenges, but also exciting opportunities. In our previous five-article series in Caribbean Compass, we detailed the electric motor conversion of our 42-foot monohull built in 1979.
Since then, we have made a few systems changes. At the time of our Atlantic passage, she was equipped with approximately 15 kWh of lithium batteries, a 5.5 kW diesel generator with an 80-gallon tank, 2,500 watts of solar, and hydro generation capacity. These systems were designed to support both propulsion and house power during long passages.
Here, we’ll delve into the critical decisions and preparations that made this ambitious crossing possible, focusing on route options, energy management, and systems preparation.
Route Options
Bermuda Route: This traditional route takes sailors north to Bermuda before heading east toward the Azores. It has stronger winds, but also significant waves and unpredictable storms; it is approximately 2,800 nautical miles. High winds keep a boat moving, but increased sea states and limited sunshine demand robust energy management for electric boats.
Modified Rhumb Line: This option lies between the direct rhumb line and the Bermuda route, skirting Bermuda by 200-300 nautical miles. It has the potential for favorable winds. It also includes calm sections, which can be challenging for boats without significant auxiliary propulsion range. It is a compromise for many sailors, but they often arrive with the fuel gauge at or near zero.
Direct Rhumb Line: At approximately 2,200 nautical miles, this is the shortest route, and the light winds and high-pressure systems are advantageous for solar-electric systems. The minimal sea state reduces drag, while clear skies maximize solar power generation. Reliance on solar and careful energy management underscores the importance of having backup generators and efficient energy storage.
For our (north)eastward journey from St. Martin to the Azores, we chose the direct rhumb line, which offered ideal conditions for our solar-electric system. With that thought and a new asymmetrical spinnaker to take full advantage of light winds, we felt reasonably confident in our choice.
Optimize Energy Systems
One of the most critical aspects of planning for this journey was ensuring that we had enough power. With our electric motor-powered boat, we believed it would be essential to rely on both solar power and contingency systems.
Solar Power: Our 2,500-watt solar array is an important component of our energy system. It’s split between panels mounted on the bimini and the davits, providing a broad and consistent surface area to collect solar energy. Of this, 2,100 watts are dedicated to charging the 48V propulsion batteries, while 400 watts support the 12V house systems, so even on overcast days, we can still generate enough power to keep the boat running efficiently.
Diesel Generator: While solar power would be our primary energy source, our diesel generator provides an additional 300 hours of runtime on its own fuel supply. This fuel reserve would serve as a safety net, giving us the confidence to sail directly into high-pressure zones with minimal concern about depleting our batteries.
Lithium Batteries: By the time of this crossing, we knew our high-capacity lithium batteries were nearing the end of their operational lifespan. While they were still functional, we had already begun noticing reduced capacity and charge-holding capabilities. In future instalments of this series, we’ll go into more detail about how the batteries performed and how we adapted our strategies in response to this issue.
Energy Management: One of the keys to successful electric propulsion on long ocean passages is careful energy management. We planned to operate the electric motor primarily during daylight hours when solar input would be highest, relying on the sunlight to recharge the batteries. At night, we would reduce our energy consumption by limiting non-essential systems and using our diesel generator sparingly.
Harnessing the (light) Winds: Recognizing the importance of maximizing wind energy for propulsion, we added an asymmetrical spinnaker for very light wind sailing. By optimizing sail trim and deploying the appropriate sail for conditions, we hoped to reduce our reliance on stored energy and extend our range significantly in calm weather.
Detailed Preparations
A successful crossing requires thorough preparation well in advance of departure. In addition to the obligatory safety checks and equipment (life rafts, EPIRBs, rig check, etc.) our pre-departure preparation focused especially on ensuring that our systems were in top working order and that we could respond effectively to any challenges that might arise during the journey. We also picked up a few additional electronics spares, which would be critical about one week into the passage.
Weather Research: One of the most important aspects of our planning is understanding the weather systems we could encounter, particularly the high-pressure zones we would sail through. These zones are typically characterized by light winds, but we could use them to our advantage. They are very dynamic and their position/location moves daily, but knowing when and where to expect these calms would allow us to plan our energy usage carefully, conserving battery power for when we needed it most.
System Testing: Before embarking on the crossing, we conducted extensive system testing, simulating the conditions of the Atlantic passage. This involved running our electric motor for long stretches at various speeds, testing how efficiently our solar array could recharge the batteries, and ensuring our backup generator would perform as expected under load.
Contingency Planning: To mitigate risks, we ensured that we had spare parts for critical systems such as our motor controller and battery management system, as well as tools for emergency repairs. Additionally, we had redundant navigation and communication systems to keep us connected to shore support if needed.
Closing Thoughts
Planning an Atlantic crossing with an electric motor requires careful coordination of energy systems, route selection, and contingency strategies. By embracing the unique challenges and opportunities presented by calm conditions and the direct rhumb line, we were able to prepare ourselves for a successful journey. In the next articles, we will dive into the realities of the crossing itself — exploring how our plans held up in practice, the surprises we encountered, and the lessons we learned along the way.
Now Read: Crossing the Atlantic, an Electric-Powered Passage: Part II
If you have any questions or would like to discuss sailboat electrification, feel free to email the authors at sail.vagari@gmail.com. Look for additional installments of this series at caribbeancompass.com.
