Electric Philosophy vs. Reality

Dieter Loibner | Professional BoatBuilder Magazine

Propelled by sunlight converted into electric power by rooftop solar panels, the custom-built catamaran Electric Philosophy pushes into an adverse current.

An Iowa couple reviews the first 3,000 nautical miles on Electric Philosophy, their custom built solar-electric catamaran, and their preparations for an off-grid adventure cruise to high latitudes.

We commissioned our boat, Electric Philosophy, in 2019 to be designed and built by Devlin Designing Boatbuilders of Olympia, Washington, around the solar electric propulsion system we specified and installed (see “North with the Sun,” Professional BoatBuilder No. 189). Sam Devlin drew the 41′ 8.5″ (12.7m) catamaran within the design limitations we posed, and permitted us to work alongside the crew to assemble and install the solar electric system as they built the boat around us. See Solar Sal for another solar-electric boat built to Devlin’s design.Now, with 3,000 nm under the keel and our expectations met, we plan to cruise to Alaska in summer 2023.

The boat was designed for comfortable medium-range coastal cruising—the ability to run at an average speed of at least 5 knots through remote areas, where electric shore power is not readily available, while still having the power to live comfortably aboard without a generator. We will be cruising mostly during the day, with the occasional overnight passage. Being retired, we have the luxury of waiting out rough weather or adverse winds and currents in port or at anchor, so our schedule is always flexible. Electric Philosophy is not intended for cruising in the open ocean for multiple days.

Our need to gather and store sufficient electric power defined the design, so its most important element was a large, unobstructed solar array. We learned from our solar-modified Airstream trailer that a couple living comfortably full-time in a trailer (or boat) will use significant energy every day. We call this our daily house load.

Not including the drive motors, it covers energy-hungry items such as the electric galley, hydronic hot water and heating system, lighting, navigation, radio, AIS, autopilot, charging personal electronic devices, and infrequent but big house loads such as the anchor winch and crab pot puller. Our galley included a large electric refrigerator/freezer and an induction cooktop, as well as an electric water kettle, a toaster, and a convection microwave oven. Occasional loads would include charging batteries for the electric outboard and electric bikes.

By the time we added the control and monitoring instrumentation and the battery management system (BMS), our electrical demand was appreciably higher than initially expected. We also wanted ample overhead lighting, and fans for the hydronic heating system. We designed the house batteries and inverter/charging system with that long list in mind.

Design Requirements

  • Very large unobstructed solar array, with no shading from boat components
  • Four large, separate battery banks; two for house loads, two for propulsion
  • Twin electric-drive motors with conventional driveshafts and oil-filled dripless seals
  • Top speed of just over 8 kts
  • Desired daily run time usually < 8 hours
  • Ability to do (occasional) overnight passage at 5 kts on batteries alone
  • Self-storing electric drum anchor windlass and electric crab pot puller
  • Fully functional galley with induction cooktop
  • Diesel-fired hydronic cabin heating and hot-water system
  • Large freshwater tanks (2x 150 gal/568 l each)
  • Large blackwater and graywater tanks (100 gal/379 l each)
  • Separate head and shower
  • Complete living area on main deck level; no accommodation in the hulls
  • Walk-around queen bed master suite with additional drop-down dinette queen bed for guests
  • Covered walkways and cockpit
  • Side entry to main deck

(Note: These personal design options won’t affect the performance of the boat. The solar array, battery banks, and drive motors are important components that directly affect the boat’s performance as a comfortable cruiser. We will discuss them in detail later in the main text.)

The Battery Banks

Two of the trickiest areas in designing an all-solar-electric cruising boat are determining the required propulsion power for the expected distance and speed of one’s daily travels and estimating the daily energy use for the house loads. Those needs must be balanced by the total daily solar input from the panels. Only then could we determine capacity and design of the battery banks.

Eileen Pauley

A house battery bank (foreground, white) and propulsion bank (green, background) share space in a hull with wastewater and freshwater tanks underneath.

Calculating total energy needs for electric vessels is fairly straightforward if the maximum distance of daily travel is known, and the boat is plugged in at the end of every day (see “Under the Sun,” PBB No. 195). But for Electric Philosophy, which runs off solar alone, does not have a fixed schedule, and uses lots of electricity, designing the battery banks and minimum solar requirements is more difficult.

Early on, we decided to configure the system with four independent and completely separate battery banks—two to power the propulsion systems (48V) and two for house systems (24V). These battery banks should be symmetrical and divided between the catamaran hulls, one house and one propulsion bank in each hull. Each battery bank was built by first paralleling the individual cells and then wiring them in series to get the final battery voltage (see “North with the Sun,” PBB No. 189).

The minimum size of each propulsion bank was based on an average draw of about 5 kWh for both motors combined and a minimum travel time of about 30 hours (including an overnight passage), which penciled out to 150 kWh (5 x 30), which meant each propulsion battery bank must have a capacity of 75 kWh. As it turned out, a slightly larger 80-kWh battery bank is a nice size if you plan to use 200-Ah lithium iron phosphate cells. You can wire eight of them in parallel and wire 16 of these cells in series to make a nominal 48V battery. You even get a little over 80 kWh of capacity, or 160 kWh total for both motors. For symmetry and because we wanted large house banks, we made them exactly half the size of the propulsion banks. For the house banks we wired 100-Ah cells, 16 in parallel instead of the eight 200-Ah cells in the propulsion banks. We used the 100-Ah cells because they were about one-third lighter, but the 16 were much more time-consuming to work with.

Eileen Pauley

During the boat’s construction at Devlin Designing Boatbuilders, Ed and Eileen Pauley installed components of the drivetrains, including the propulsion battery banks and the motors.

Large battery banks are expensive, but they provide the capacity for the 30 hours run time at 5 kts we wanted. More importantly, a nominally large continuous draw (or charge) represents a small percentage of the total battery capacity and therefore puts less stress on the batteries, which makes them less likely to heat up, so temperature control is not an issue.

Preparations for Our Trip to Alaska

We spent this past winter getting ready for a planned trip up the Inside Passage to Alaska from mid-May through July 2023. We brought thevmotors and Sevcon controllers back to Electric Yacht (Golden Valley, Minnesota) in December for software updates and purchased the latest digital display as part of the deal. Scott McMillan of Electric Yacht has been very supportive of our project in spite of the fact that it isn’t a typical application for his systems—he specializes in diesel-to-electric power conversions on sailboats. To date, it still might be the first, and we think the only, case of continuous operation of Electric Yacht’s motors on a powerboat. Much to our surprise, the belts and pulleys show almost no wear after the first 500 hours (3,000 nm) of use.

Eileen Pauley

In the first iteration, the Pauleys installed dual 10-kW motors from Electric Yacht in the starboard
hull and a single on port.

But technology does not stand still. The company’s newest water-cooled 15-kW units could be a perfect fit for Electric Philosophy, because we noticed less than a half-knot speed drop when going from 40 kW to 30 kW of output with our current motors. Besides, water-cooled units are much smoother and quieter, and there would be only one motor and belt per side instead of two, which would improve drive efficiency and quietness. But simplicity is also an asset. Not having the water cooling and the throughhulls that go with it is an advantage. While we won’t make such a big change before the Alaska adventure, we’ll consider a conversion in the future.

As mentioned in the main text, during spring haulout we’ll adjust prop pitch to more closely match the drive ratio we now have, which should further reduce prop singing. If we repower with watercooled motors, we would also look at a lower speed ratio (Electric Yacht offers more options with the 15-kW units) and higher pitched props.

Our anchor/winch system was originally fitted with 33′ (10m) of 10mm (0.39″) chain and about 450′ (137m) of rope. For our Alaska trip we are switching to 130′ (40m) of 5⁄16″ (8mm) Grade 43 high-test chain and less rope. This should be a better rode for the conditions we expect to see on the Inside Passage. We have observed that with the rope rode and the shallow-draft catamaran hulls, we swing very differently at anchor than monohulls on full chain.

We currently store the dinghy connected to Weaver snap davits and tipped up against the aft roof-support poles. In rough waters, the waves between the hulls wash up against the dinghy floor and over the bulwarks onto the cockpit. Another spring project is to install davit hooks to carry the dinghy above the swim step.

One item we are adding for the Alaska adventure is a StarLink system for remote Internet access. The In-Motion antenna dish will be mounted aft of the roof. This will be one more electrical draw that we will need to monitor carefully and use selectively.

We are leaving behind our e-bikes on this trip, but a portable freezer is going along with hopes of successful fishing—yet another electrical draw to monitor if used.

—Ed and Eileen Pauley

Next, we determined our expected daily energy use. Assuming our average cruising day is about eight hours, and our average draw of the motors is 5 kW, we’d need about 40 kWh per day; and on a travel day we could use close to 10 kWh of energy for all house loads. The question was how to configure the solar panels to charge the battery banks. Keeping each battery bank electrically separate from the others required an inverter/charger and a solar charge controller for each bank. We divided the solar panel wiring so each bank would draw power only from its dedicated panels.

Eileen Pauley

Sixteen of these 100-Ah house battery cells are wired in parallel, totaling about half the size of the propulsion banks.


Of the 25 rooftop 380-watt panels (9,500 watts total) with 36V nominal output, 20 (about 7,600 watts) are used for propulsion (10 for each drive bank). An even number of panels was needed for each drive bank, because the 36-watt nominal output panels had to be paired in series of two to supply 72V for the two banks’ 48V solar charge controllers. We need 72V because the charging voltage for a nominal 48V lithium battery is about 55V, and we require a minimum of just over 60V to the charge controller to supply this charge voltage. On the other hand, the twin house banks could use single panels to supply 36V to their 24V solar charge controllers.

The total solar energy the panels will receive on an average day is usually estimated as 5 full solar hour equivalents per day multiplied by the solar capacity of the panels. Running the numbers: 7,600 watts x 5 = 38,000 Wh (about 40 kWh) per day available to run the motors. Recall that the total capacity of the propulsion battery banks is 160 kWh, or four times this daily solar input. This means that if we make a long passage in poor weather or adverse currents, or travel at higher speeds and use more than 40 kWh of energy, it might take more than a day to fully recharge the propulsion banks. This was the case more than once this past summer, but then we knew we’d be spending more than a day at the next stop. We included a shore-power connection in the build to help charge the banks if absolutely necessary but so far have neither used nor needed it while cruising.

Eileen Pauley

Of the twenty-five 380-watt solar panels with 36V nominal output, 10 pairs charge the propulsion batteries via 48V solar charge controllers.


A side benefit of the separate inverter/chargers for each battery bank is that power outlets from each bank can allow us to shift some 110AC house loads to a propulsion bank inverter if we have been moored for a few days and the propulsion banks are fully charged. A label on every outlet on the boat indicates which bank supplies the power to it.

The remaining five solar panels provide 1,900 watts x 5 hours = 9,500 Wh (about 10 kWh) per day for house loads, with three charging the starboard house bank and two the port-side bank. We then split the house load circuits to approximately 60% starboard and 40% port, which worked out well.

It is important to remember that many house loads continue when propulsion is not used, often through the night. While our total electric use is on the high side, we would suggest that a cruising couple with modern household amenities on an all-electric boat should budget a minimum of 1,500 watts of solar for the house loads. Even 2,000 watts would not be unreasonable for a boat like ours.

While traveling, we learned about unexpected obstacles to charging. For example, shading of the solar panels—even a small amount of shadow—while we are docked significantly reduces charging input. At times, we turned the boat or selected a different slip to avoid dock pilings, neighboring boats’ masts, or flybridges that would shade our roof. When anchoring, we are always mindful of rock walls or trees that may cast a shadow on the panels. The radar pylon’s mounting at the bow of the boat makes for a nontraditional profile, but its position avoids solar shading.

Finishing and Troubleshooting

In August 2020, at the height of the COVID-19 pandemic and when the first article about Electric Philosophy was taking shape, we finished installing and wiring the battery banks in the hulls while the builders were getting ready to install the deck and complete the boat’s construction. We continued to work on the battery chargers, solar panels, motor components, and wiring, mostly in the evenings and the weekends, when the build crew was not glassing, painting, or sanding. As construction moved along, we struggled to keep up with our part. We feel badly for people whose lives were disrupted by the pandemic, but the cancellation of all our prior commitments for 2020 and 2021 did free us to work on the boat full time. We needed every minute to finish the boat to splash on July 7, 2021, near Devlin’s shop.

Eileen Pauley

Tow testing with a load cell determined hull drag.

The boat was towed without propellers to Swantown Boatworks, also in Olympia, where it went on the hard for final fit-out.

We cruised the boat through late October in Puget Sound and worked out new bugs. Of the two significant, costly, time-consuming issues, one was related to the solar electric system, the other not. The central processing units (CPUs) of the BMS we had purchased from Elite Power Solutions had hardware and software challenges we couldn’t overcome. So in the spring of 2022 we switched to an Orion BMS, which allowed more direct programming, monitoring, and trouble­shooting.

The other issue was failure of a Cutless bearing and shaft seals that required multiple haulouts to fully address. The prop shaft support system included the bearing at the motor housing, plus three Cutless bearings—
one at the front of the stern tube, one at the rear of the stern tube, and one in the strut. After the front tube Cutless bearing failed, causing damage to the shaft seal, they were repaired in October. We did some research over the winter and concluded the shaft was likely over-constrained with three Cutless bearings. In the spring, we removed the front bearing, and since then, we have covered 2,200 nm with no problems.

Eileen Pauley

To test efficacy and smoothness during operation, the Pauleys fitted two 20″-diameter (50.8cm) propellers, one with two blades to port, the other with three blades to starboard. They settled on the three-blade prop.

Our primary goals in selecting propellers were efficiency and quiet running. We expected a two-blade design to be more efficient, while a three-blade design would likely be smoother. As the boat was an ongoing experiment, we decided to try one of each with the same 20″ (50.8cm) diameter to compare. We chose the smoother three-blade version with the port prop LH, starboard prop RH. Because the motor mounting frames were designed to accept single or dual 10-kW [13.4-hp] motors, we also tried the mix and match approach with the electric motors from Electric Yacht (Golden Valley, Minnesota). Starting with a single 10-kW motor on port and dual 10-kW motors (total 20-kW output) on starboard, we found the 10-kW single motor was challenged by continuous operation at higher loads when we were bucking wind or current, so we added a second motor to the port side. We now have matching 20-kW motors and three-blade props on each hull.

Eileen Pauley

In an effort to quiet the persistent propeller whine at slow speeds, the Pauleys hauled Electric Philosophy to have the blades cupped on their trailing 

During the April 2022 haulout, we shifted the motors aft several centimeters to move the propellers back for more clearance between the prop and hull to reduce the rumble/vibration and gain room to install a set of line cutters. We still noticed a loud and very annoying propeller whine, known as propeller singing, at maneuvering speeds. It’s not unusual and would likely be covered up by the engine and drivetrain noise on fossil-fuel-powered boats, but on a quiet vessel like Electric Philosophy, particularly at low speeds, it is noticeable and irritating. We were lucky that Brandon Davis from Turn Point Design [see “Repairing a Cored Carbon Hull,” PBB No. 201, page 50], who visited the boat one day in Port Townsend, diagnosed the problem at once.

We hauled out again in August 2022, in Port Townsend, to have the Shipwrights Co-Op [see “Cooperative Incorporated,” PBB No. 193, page 62] modify the propellers to try to fix the singing problem. This turned out to be more involved than the “normal” fix of grinding a chamfered edge on the suction side of the trailing edge of each blade. Our Michigan Wheel props already had an anti-singing edge, so the Co-Op suggested we cup the trailing edges to modify the vortices that produce the noise. This did indeed remove most of the singing but also added pitch to the props and a new problem: now the motor drives worked at the wrong ratio. Because of the increased pitch, we had to reduce prop speed by changing belt pulleys to adjust the ratio.

During the spring 2023 haulout we will adjust the pitch to match the new prop speed ratio. Our observation is that low-pitch props are more susceptible to singing than higher pitch props, something electric-boat builders should be aware of when choosing prop and drive systems.

Eileen Pauley

Ed Pauley configures the settings of a new battery management system on a laptop computer.

We also encountered several minor but notable electrical cable and wiring issues. We found a bad control cable (poor internal crimp fitting connection) on the hydronic heating system, and another one on one of the motor controllers. We also were bothered by a poorly crimped, hard-to-find connection on one of the main motor cables.

Our 24V house banks yielded one unfortunate incident. We tried to source as many 24V components as we could and run any 12V-items like the VHF on a DC-DC converter. We chose Simrad chart plotters that could operate on 24V but realized too late that the NMEA 2000 backbone runs only on 12V. After accidentally connecting 24V to the NMEA 2000 backbone, all the NMEA 2000 wiring had to be replaced.

One of the motor relays and one of the BMS relays failed closed, a minor issue but hard to diagnose. We have also had the normal wiring challenges (bad connections, etc.) that you would expect on a system with thousands of crimped and heat-shrink connections. In one respect, we are surprised there weren’t more hiccups.

We diagnosed and corrected all these issues ourselves, and none stopped us from completing a passage. A big help in diagnosing and troubleshooting wiring problems is that we did all the wiring for the batteries, BMS, solar, and motors and drew up a complete set of wiring diagrams for the boat. We also compiled an owner’s manual detailing all the systems and components along with their specifications and operation. It has come in handy when sourcing spare parts, for familiarizing guests with the operation of the boat, or just jogging our seasonal memories.

Eileen Pauley

Electric Philosophy under way at Swantown Harbor in Olympia, Washington.

The Road Thus Far

After launching, we lived aboard Electric Philosophy from July to November of 2021 and from April through October of 2022, accumulating approximately 3,000 nm of travel. In the off-season we store her in a boathouse in Olympia. We have cruised the entire length of Puget Sound multiple times and spent a summer in the San Juan Islands and Canadian Gulf Islands. Electric Philosophy was also on display at Port Townsend Wooden Boat Festival 2022, with many visitors touring the boat and complimenting its design, fit, finish, and execution of the solar cruising concept. Part of the vessel’s appeal is the large windows all around and the skylights that create bright and airy accommodations, combined with deck-level accommodations with no steps. Walnut from our Iowa property accents details in counters, drawer fronts, tabletops, and ceiling trim. It’s also a nice visual connection to our home on dry land.

Eileen Pauley

The dinette table and other interior surfaces and trim are walnut wood from the couple’s Iowa property.

Overall, we are very pleased with the performance of the boat. It is quiet at speed but not completely silent since there are four motors with the requisite belts and pulleys. Guests who rode with us came away impressed with the smoothness and quietness of the boat, and we enjoyed sharing the experience with several overnight visitors.

The large tanks give us flexibility for choosing pump-out facilities and freshwater fill-ups. Perhaps most gratifying has been not caring about the soaring price of diesel, as we stopped at a fuel dock only to top up the small tank for the hydronic heater at the end of the season before winter storage.

We are also satisfied with the efficiency of the hull and drivetrain. We can do the intended 5 actual knots through the water using 5 kW total energy for both motors combined, which is quite good for a 41′ boat with a displacement of approximately 26,000 lbs (11.8 t).

Answers to Our Most Frequently Asked Questions

How far can we go? What is our average cruising speed and our top speed? The most frequent and usually the first question people ask when they see the boat and meet us is about range without recharging the batteries. In truth, there is no limit since we don’t generally travel at night, and we can always slow down to conserve batteries. We go slower if we are on a (rare) long passage against tides and/or currents or are in cloudy/rainy conditions for an extended time. On the other hand, we have become fairly proficient at watching the tides and wind and traveling when they are favorable, which translates into more speed and greater distance. Our longest day trip so far is 82 nm at an average speed of more than 7 kts, taking advantage of favorable tides and wind. This is the reason our average speed over the first 3,000 nm is nearly 6 kts. Our top speed is about 8.5 kts in calm conditions, but at that speed the motors are drawing the max 40 kW total power, so it is not a sensible travel speed.

Eileen Pauley

A welcome addition to the menu is fresh caught crab.

How often do we need to clean the panels, and how do we do it? We watch the panels and try to clean them as needed, about every two to three weeks. Seagull droppings are one of the most common reasons to clean, because they are opaque and obscure the panel surface. We have found the easiest way to do this job is with a commercial window cleaning sponge/ squeegee combination on a long, adjustable pole. We carry a 6′ (1.8m) fiberglass stepladder to set up on a dock next to the boat. We rinse the sponge between panels with fresh water and then use a microfiber towel to wipe down each panel. The panels also attract normal dirt like airborne soot, particularly during the smoky Pacific Northwest summer of 2022. While this kind of grime can cover the panels with a heavy layer, it does not interfere with solar output as much as one might think. It’s worth noting that the panels all have a slight slope, so they get washed in a good rain. We paid particular attention to the placement of the radar mast on the bow of the boat, where it does not shade the panels. Radio antennae are thin and mounted at the front corners of the roof. It should be noted that even a small amount of shade on a large solar panel results in a disproportionately significant reduction in solar output.

How easy is it to use the boat—crabbing, mooring balls, anchoring, dinghy, etc.? Because the bulwarks are low to the water, it is convenient to pick up mooring balls, launch and retrieve the anchor, and from the swim platforms on each hull retrieve the dinghy, and to use the boat for crabbing (the builder installed a crab pot puller on the port stern). Our crabbing experience started slowly, but eventually we had a good harvest, at least until the last day of the season, when one pot went missing. The side deck entry gate is especially appreciated, making walking onto the boat from a dock safe and convenient. The fully covered walkways and cockpit offer shelter from sun and rain. We are satisfied with our choice of a drum anchor winch (Lonestar Marine GX-5), although it took some getting used to due to its power. We found that our original anchor with a straight shank did not fit well through the opening in the forward bulwark, so we replaced our original hook with a Rocna Vulcan (55 lbs/25 kg), whose curved shank tracks easily through the opening. On the seabeds we’ve encountered, this anchor holds well and is easy to launch and retrieve.

—E.P. and E.P.