I struggle to descend the stairs leading to the sandy beach at Half Moon Bay, California, awkwardly hefting the 60-pound solar-powered SeaCharger atop my shoulder. Amid numerous “what-the-heck-is-that?!” stares, I perform some last-minute checks of the propeller and rudder, then wade out knee-deep and push SeaCharger as hard as I can toward the oncoming waves

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