What is the market for robot fish?

Currently there isn’t one, apart from the rather trivial entertainment markets: aquarium toys and amusement park attractions.

“Serious” robot fish researchers usually justify themselves through some combination of the following.

  1. 1.The Efficiency Argument. Many people are impressed by biological swimmers (dolphins, sharks, penguins, et cetera according to taste) and argue that they must be exceptionally efficient. This dates at least back to the thirties when Sir James Gray estimated how much muscle power a dolphin should have and how much power it should take to propel a dolphin-shaped object through the water at dolphinesque speeds. “Gray's Paradox” is that the dolphin shouldn't be able to swim anywhere near as fast as it does. Since then various flaws have been exposed in Gray’s calculations, but some people still think there’s something to it.

    So if dolphins (sharks, penguins, et cetera) are doing something special—if, for example, they manage to recapture energy from their own wake, thus reducing their effective drag—perhaps we can usefully copy that. If a robot dolphin could swim twice as far as a “conventional” submersible on the same battery charge, then we’d use robot dolphins to inspect off-shore oil rigs, do oceanography and underwater archaeology, rescue sailors, spy on enemy submarines, and so forth. Maybe the same techniques could also make surface boats and ships more efficient.

    By the way, there are also skeptics who will tell you this is a fool’s errand and dolphins are really less efficient than propeller-driven boats. I am currently agnostic but perhaps leaning more towards belief than disbelief.

  2. 2.The Stealth Argument. A variation on the efficiency argument is that if a robot fish recaptures energy from its wake, it will make less noise in the water. Also, whatever noise it does make will presumably sound more like a fish and not like a normal boat. So perhaps a fish-like vehicle would be good for sneaking up on an enemy submarine or a sea creature you wanted to monitor or catch.

  3. 3.The Maneuverability Argument. Fish are also notably more maneuverable than the average boat. Some fish can make a 180-degree turn in one body length. Predatory fish accelerate at 10 gees from a dead stop. I believe this is largely because they are relying on so-called added-mass forces (proportional to acceleration) instead of the lift force (proportional to velocity squared) that acts on a propeller blade. There might be a role for vehicles which work in the same way.

  4. 4.The Pure Science (Biology) Argument. By building robot fish (dolphins, penguins, turtles) we understand better how real fish (dolphins, penguins, turtles) swim. Even if we don't want to copy that manner of swimming ourselves, we'll understand the animals that much better. Maybe there will be some practical payoff in fisheries or wildlife management.

  5. 5.The Pure Science (Control Theory) Argument. A fishlike swimmer is a system that isn’t easily controllable. Even if there’s no practical demand for artificial fish, it’s an interesting intellectual exercise to figure out how to control them. The same control methods might be applied to other difficult systems.