The purpose of this project was to see if a submersible propelled by an oscillating tail would prevail in speed over a propeller-propelled version of the same model. The hypothesis, based on the fact that tuna and some other large predatory fish can reach 80 kilometer per hour while using much less energy than vessels, stated that the tail-propelled unit would be faster than the propeller-propelled unit. However, the question of this project, “Is there a more efficient way for submersible propulsion?” would only be answered if the hypothesis were accepted. Nonetheless, this project was not totally in vain. Much knowledge was obtained from this project, and this project opened hundreds and thousands of new possibilities for faster and more efficient submersibles.
To accomplish this, a basic frame of basswood with balsa stringers was constructed. Small custom-made hinges were made to give the tail the freedom to swing at almost 360 degrees. The tail-propulsion unit was located between the ribs in the middle of the model and the propeller-propulsion unit was hung down at the bottom of the frame. The revolution speed of the motor was reduced while the power increased through a gearbox; an obliquely centered wheel connected to one of the shafts on the gearbox was used to convert the spinning movement of the shaft to back and forth movement used to drive the tail. Almost all construction technique, material, and configuration were founded by trial and error. The results were rather disappointing. The tail-propulsion unit could not even push the submersible at one kilometer per hour. In fact, the fastest speed was 7 times slower than that. The tail-propulsion unit only achieved 1 meter in 22.47 seconds fastest, or 60.87 seconds slowest. Even the fastest speed was 10 times slower than the propeller-propelled unit. The propeller unit did not do much better, the unit reached 1 meter in 2.11 seconds fastest to 9.47 seconds slowest despite the fact that many mini experiments were done to find the right size of the propeller. These results were probably caused by many reasons. One, the surface area of the tail seemed to create too much resistance, which seemed to be one of the major reasons that caused the slow movement of the submersible. Also, the water slowed the motor. Another reason was that the gearbox and the tail-propulsion system was very inefficient in converting spinning movements to back and forth movements.
If this project were to be repeated, several factors should be changed. For instance, the size of the submersible should be greatly reduced. In addition, the transmission system should be replaced, and the hull probably should be sealed to reduce water resistance. In addition, here are some ideas for further study:
Will a smaller submersible be faster than a larger submersible?
Will a twin motor system with pulse-generator produce a faster model?
Is there a different approach possible for submersible propulsion?
Is a tail-propelled submersible more efficient in fields such as turns, dives,
accelerations, et cetera?
Will a flexible membranous tail increase efficiency?
download the excel data file here