Setting a bottle adrift with a message in it is, by most measures, an act of desperation. The sea regularly swats mighty ships to their doom, so what chance would a tiny glass bottle have bobbing along the surface, subject as it is to wind, waves, and current? Little to none, it would seem, unless you skew the odds a bit with a wave-powered undersea glider to the help the bottle along.

Before anyone gets too worked up about this, [Rulof Maker]’s “Sea Glider” is about a low-tech as a device with moving parts can be. This craft, built from a scrap of teak and a busted wooden ruler, is something that could be assembled in a few hours from whatever you have on hand, even if you’re marooned on an uncharted desert isle. The body of the craft sprouts a set of horizontal planes that can swivel up and down independently. The key to providing a modicum of thrust is that each plane is limited to a 90° swing by stop blocks above and below the pivot. The weighted glider, tethered to the bottle, bobs up and down below the waves, flapping the planes and providing a tiny bit of thrust.

Was it enough to propel the bottle any great distance? We won’t ruin the surprise, but we will say that [Rulof]’s essentially zero-cost build appears to have improved the message in a bottle bandwidth at least somewhat. It’s not a Hackaday Prize-winning robotic sea glider, but it’s a neat hack nonetheless.

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