Biomimetic Propless Submersible Propulsion

Reducing detectable vehicle presence during submerged operation using a biomimicry buoyancy-derived propless propulsion system.

Illustration of the variable-geometry displacement propulsion system test platform.

I have recently been contacted about some of my earlier designs, including a concept for submarine propulsion through variable-geometry changes in water displacement. Using a vessel’s buoyancy like a sailplane uses its height to generate forward movement, this system would be more efficient as a submerged vessel can use both positive and negative buoyancy in order to generate continuous forward motion by rising up and then sinking back down in slow gentle cycles.

Due to the density of water, wings would be much smaller for a submersible than for an aeroplane, while traditional lifting structures are unnecessary for a submerged vessel using this form of propulsion – any control surface that simply resists direct ascent and descent is all that is necessary. My kids demonstrate this principle when playing in the pool with a buoyant foam kick-board. Sinking the board and then releasing it will cause it to rise at a rapid rate. Released at an agle, the board will shoot forward across the pool as it rises.

Like a fish’s air bladder, changes in the amount of water displaced by the vessel change whether it sinks or floats. Most subs use compressed air to push water from bouyancy tanks in order to surface and allow water in to descend, but this consumes a lot of compressed air and is far from quiet. Another option is to change the shape of part or all of the vessel, expanding to rise and contracting to descend. This can be done mechanically, by using a pump to move fluid hydraulically, or by using waxes and other materials that expand when heated.

Borrowing from nature, biomimetic designs carry advantages derived from many thousands of years of optimization. These designs allow us to improve our mechanisms and move with a significantly reduced impact on the environment. Becoming less intrusive may let us observe the natural marine ecology without having to be a ‘noisy neighbor’ frightening everything into hiding when we pass by.

Additional strategies could further improve vessel stealth by designing the outer shape to mimic large animals (rays and whales for example), by using digitized natural sounds for echolocation, and by installing anechoic foam around the hull to better simulate a living organism.

A more complete description of this design is available on my personal blog: