Did a Solar-Powered Autonomous Boat Just Cross the Pacific Ocean?

Arduino Drones & Vehicles Energy & Sustainability Science
Did a Solar-Powered Autonomous Boat Just Cross the Pacific Ocean?
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I struggle to descend the stairs leading to the sandy beach at Half Moon Bay, California, awkwardly hefting the 60-pound solar-powered boat SeaCharger atop my shoulder. Amid the numerous “what-the-heck-is-that?!” stares of the beachgoers, I perform some last-minute checks of the boat’s propeller and rudder and then wade out into the knee-high surf and push SeaCharger as hard as I can towards the oncoming waves. Moving at walking speed, the boat makes it through the first several waves without being flipped. Relieved, I make my way back up onto the beach, then turn around and watch my two-and-a-half-year project slowly plodding westward, gradually disappearing in the whitecaps.

An older man who has been watching the entire time approaches me and tells me that he’s sorry that I lost control of my boat and that he’s sure it’ll wash up on the beach somewhere. I assure him that the boat is on autopilot, going exactly where it’s supposed to be going. “And where is that?” he asks. “Hawaii.” The look on his face is priceless.

Indeed, the idea of this tiny, homemade boat surviving 2,400 miles of open ocean to reach Hawaii seems foolishly unrealistic, and I know that more than anybody else. With help from friends, I built the eight-foot-long, autonomous, foam-and-fiberglass, solar-powered SeaCharger in my garage – not to make money or to win a contest, but simply as a challenge. And a challenge it was. What started out as a year-long project turned into 30 months of mistakes, compromises, and start-overs. So for the next couple of hours, I spend my time worrying and fretting, glued to the screen of my phone, waiting for each telemetry report sent by SeaCharger’s satellite modem. When it becomes obvious that the boat is still on track and doing well, I get in my truck and drive home.


For the next day or two, SeaCharger appears to be doing remarkably well. It’s windy off the coast of California, and I can tell from the attitude sensor on board that SeaCharger is heeling sharply in the wind. Yet the boat keeps making its way westward, slowly but surely, reporting in every two hours via satellite. Even at night the boat keeps moving, having collected and stored solar energy in its large lithium-iron phosphate battery pack.

Then, Monday morning, after being at sea only two days, the boat fails to send its normal update. It is not completely unheard-of for it to miss an update – sometimes the position of the satellites overhead does not provide a strong enough signal – but it’s very rare. So I anxiously wait another two hours for the next update. Again, nothing. The boat is dead, and I know it. Never during all the previous testing has it ever missed two updates in a row. I tell a friend what has happened, that the boat must have sprung a leak or been eaten by a shark, but that one way or another, it’s dead. My friend replies by telling me that he has a feeling that the boat will be fine. I find his reassurance unreasonable, but strangely comforting. Sure enough, two hours later, SeaCharger miraculously checks in again, and I breathe a sigh of relief.

Problems occur over and over again during the next few weeks: the motor controller unexpectedly stops and has to be reset, strong currents almost halt the boat’s progress, a cloudy day causes the boat’s batteries to run out of juice. Each time, the only information I have is that the boat has stopped moving. It has no weather sensors and only minimal diagnostic sensors. Extra sensors would not only be expensive, but also risky: increased complexity means that there are more things to break.

However, without weather or other information, it’s easy for my imagination to run wild. I often assume that one of the boat’s four homemade waterproof electrical connectors has sprung a leak. Professional-grade waterproof connectors can cost over a hundred dollars each. That wasn’t an option, so I made connector bodies out of brass plumbing fittings, adding O ring grooves using my Sherline desktop mill and potting the electrical contacts (bought at the local hobby shop) with high-quality (and expensive) 3M epoxy. The entire boat is full of assemblies such as this that combine hobby-grade or homemade components with professional-grade ones. Using purely hobby-grade components might jeopardize the boat’s reliability, but paying for purely professional-grade components might jeopardize my marriage. Where to spend the money and where to go cheap is a judgement call that had to be made time and again while designing and building SeaCharger. As the boat stumbles now and then on its journey across the Pacific, I constantly wonder if I went cheap one time too many.


One of the biggest question marks is whether the boat’s solar panels will survive. The type of solar panels that you might find on the roof of an RV are certainly not designed to be immersed in salt water, whereas SeaCharger’s solar panel deck is constantly getting drenched by corrosive seawater. Here again, simplicity proves to be key: SeaCharger’s solar panels are made only from laminated layers of plastic, doing away with the aluminum frame and the glass outer layer found in typical roof-top panels. These thin, light, semi-flexible panels may be too fragile for a typical roof-top installation where tree branches might fall on them, but they are perfect for use on the ocean, where there are no trees and where their all-plastic construction makes them almost immune to corrosion from seawater.

Renogy gave me two sets of these solar panels free of charge (this was the only sponsorship I was able to secure on this project, despite several other attempts). Extra marine sealant is applied to the panels where the electrical wires exit, and the panels are hard-wired to the boat instead of using connectors, again in the interest of simplicity and reliability. Two solar panels are used for redundancy, but there is no redundancy in any of the other components on the boat, mostly to keep costs down.

Many people (including my wife) have asked me how much the boat costs. At first I faithfully kept receipts so I could track the project’s cost, but I never had enough nerve to actually add them up, and finally I just stopped keeping them. The experience is priceless, and as I tell my wife, the reason I have a career as an engineer is because I do projects like this on my own time.

SeaCharger uses off-the-shelf electronics as much as possible. The brain of the boat is an Arduino Mega, the GPS is from Adafruit, the satellite modem is from Rock7, the compass is from Devantech, and the battery protection/charging circuit is from AA Portable Power Corp. A typical R/C model-style brushless motor spins the propeller and an R/C servo turns the rudder. In terms of reliability, I don’t worry too much about the electronics, but I do worry about the motor and the servo. Water is not the problem: the motor transfers torque to the propeller through a magnetic coupling, so it stays perfectly dry. And the servo has its own custom-made enclosure with rubber shaft seals to keep water out; this enclosure was designed and built by friends of mine, and I trust they got it right. But the bigger issue is the time required to get from California to Hawaii: the motor will have to run almost nonstop for over a month, while the rudder servo will have to complete 2–3 million cycles.


In spite of all my worrying, after 3 weeks at sea, the boat is not only still alive but is actually moving along at a very good clip. It’s almost unbelievable. For the past two and half years, amid my children’s constant cries of “Dad, when is the boat going to be done?!,” I’ve motivated myself by visualizing the moment when I’m standing on a boat ramp somewhere in Hawaii as SeaCharger appears in the distance among the waves, then comes motoring into the harbor, at which time I pull it triumphantly out of the water. Now it looks like that might actually happen!

With a project like this, visualizing the end goal turns out to be a very powerful motivator. I also rely heavily on my faith in God, praying constantly that I won’t make any catastrophically bad decisions and that the elements will be tempered. And finally, it would be difficult to overstate the importance of the encouragement received from my wife, family, and from strangers all over the world who have been watching the project progress.

Three more weeks pass. I’m now standing on the shore at Mahukona Harbor on the Big Island of Hawaii watching SeaCharger enter the harbor. This moment is not as triumphant as it is surreal. I know that this is the same SeaCharger that left California 41 days and 2,413 miles ago, but the faded paint and clinging barnacles only hint at what it must have experienced — and survived — to get here.

Safely ashore, SeaCharger appears to be in remarkably good shape. After a few dabs of touch-up paint and some reprogramming, I launch it again from Hawaii, this time headed towards New Zealand, 4,400 miles away. That’s a long way, and a million things could go wrong. There’s no way it will actually make it… is there?

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Damon McMillan

Damon McMillan is a mechanical engineer, hobbyist and father of four. He resides in Sunnyvale, CA.

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