Battery electric ferry boats may be more environmentally friendly and require less maintenance than diesel-fueled ferry boats, but they are still not perfect. Scientists are therefore currently considering powering small ferries using only compressed air.
One of the disadvantages of battery electric watercraft lies in the fact that it takes a relatively long time to charge the battery.
Others believe that batteries have a low energy density for their size and weight. Additionally, over time, batteries no longer hold a charge and must eventually be discarded.
With these issues in mind, Professor Abdul Hai Alami and colleagues at the University of Sharjah in the United Arab Emirates recently turned their attention to compressed air.
The researchers created a pneumatic drive system consisting of two 40-liter compressed air tanks connected to a 6-horsepower “air motor.” This tank is connected to the propeller via a steel shaft. When air is released from the tank at a pressure of 200 bar (2,901 psi), the motor, or propeller, spins rapidly. A gearbox can be added to adjust the speed and direction of thrust.
University of Sharjah
For the swimming pool test, the system was installed on a three- to four-person PVC boat made to resemble the Abra ferries commonly used in the United Arab Emirates.
A device known as a load cell, located poolside, was connected to the back end of the boat via a steel cable. Once the drive system was started, its thrust was measured by the pulling force on the load cell. As a contrast, the same boat was also fitted with an electric motor of similar capacity powered by a conventional battery.
In the end, the pneumatic setup was found to be able to provide 6% more propulsion along with an operating range comparable to a battery electric system with a 12 Volt/18 Ah battery pack. Additionally, researchers estimate that the pneumatic system’s annual carbon footprint is 307 kg (677 lb) lower than a comparable battery electric system.
This reduction in footprint is due in part to the proposed system, where quayside photovoltaic panels are used to power the compressor that pressurizes the tank, eliminating the need for fossil fuel-based energy sources. is not necessary. The idea is that in the time it takes for one group of passengers to disembark and another to board, the tanks will be charged and ready for departure.
That said, pneumatic drive systems will initially be limited to use on fairly short-distance ferries, and will probably also be used on recreational watercraft used near the coast.
“When a tank is depleted, the amount of available energy is systematically reduced, because starting with a tank at 200 bar provides a higher energy quality than if this pressure were reduced to 100 or 50 bar.” says Professor Alami. “Therefore, in the early stages of development, it may be dangerous to venture far from charging stations.”
A paper on this research was recently published in the academic journal Ocean Engineering.
Source: University of Sharjah (via EurekAlert)
