Portuguese 
English 
Spanish 
4 min of reading 
0 comments 
Research team from the University of Applied Sciences Kiel in Germany investigates the development of propellers with less cavitation to reduce the low-frequency noise caused by the 50,000 merchant ships operating worldwide in the oceans, which harms marine life.
Every time a vessel cuts through the seas, it is accompanied by a continuous low-frequency noise produced by the propellers that propel it, a sound that propagates for kilometers underwater and disturbs the sound environment of oceans in all regions of the planet.
This phenomenon, known as cavitation, was academically identified in 2004, although it had been studied since 1893, and is associated with the operation of virtually all propeller-driven vessels, making the scale of the problem directly proportional to the number of ships operating worldwide.
According to the International Chamber of Shipping, there are approximately 50,000 merchant ships continuously operating around the planet, and all emit this type of low-frequency underwater noise, which makes it clear that the impact is far from being localized or confined to specific routes.
-
What the Public House of Julius Caesar was like inside in the Roman Forum: layout, atrium with compluvium and impluvium, tablinium and peristyle, and the scandal of the Bona Dea, revealed in an AI recreation.
-
While digging a trench next to a pool in Germany, workers found more than 1,500 silver coins from 1320 in the rubble, revealing a treasure buried for over 700 years.
-
Flight Helios 522, the “ghost” flight with 121 people: the commercial aircraft flew for more than 2 hours on autopilot after a pressurization failure left pilots and passengers unconscious and only stopped when it ran out of fuel.
-
Researchers have located a nearly intact vessel that disappeared 125 years ago on the bottom of icy waters, with masts still preserved and rare details that impress archaeologists.
Human-generated noise pollution is the least discussed among types of aquatic pollution, but its effects are documented: whales use sound to communicate, navigate, and hunt; fish rely on sound perception to detect predators and reproduce; and crustaceans are sensitive to vibrations propagated on the ocean floor.
The relationship between intense maritime activity and ocean biodiversity is increasingly studied as the accumulated effects of decades of navigation become visible in migratory behaviors, reproductive patterns, and populations of marine species in different regions of the planet.
How cavitation generates noise in propellers
To understand the phenomenon, one must observe what happens to the blades of a propeller at high rotation: the movement creates a pressure difference between the faces of the blades, and on the rear face, the pressure drops so abruptly that the water changes state, forming thousands of small vapor bubbles.
The problem arises when these bubbles leave the low-pressure zone and violently implode upon returning to the liquid state, generating pressure waves that transmit at high speed through the water and, upon reaching surfaces, can considerably deteriorate them over time of continuous exposure.
The researchers in Kiel identified the precise moment when the sound peak occurs: not at the formation of the bubble, but at the end of the collapse, and the intensity of the impact directly depends on the speed at which this collapse happens — the faster the process, the stronger the sound generated.
The phenomenon is accompanied by vibrations and noise reminiscent of gravel falling on a machine, and this sound, although low-frequency, travels great distances underwater, reaching kilometers away from the vessel and disturbing entire marine ecosystems along the busiest routes on the planet.
The MinKav project and the propellers of the future
The team from the University of Applied Sciences Kiel has set out to tackle the problem with the MinKav Project, an initiative aimed at developing propellers that generate less cavitation, which are quieter and potentially more energy-efficient at the same time.
The logic behind efficiency is straightforward: cavitation represents wasted mechanical energy, transformed into heat and noise instead of propulsion, which means that a propeller with less cavitation can deliver the same performance with lower fuel consumption and less environmental impact per route traveled.
The experiments are conducted in the university’s Naval Hydrodynamics Laboratory, in an aquarium with a miniature propeller that accurately reproduces the flow conditions around the blades, aided by underwater microphones and high-speed cameras to identify where and when the noise peak occurs.
The next step involves computational simulations to test different propeller geometries, aiming to reduce noise without sacrificing performance, efficiency, or durability, variables that need to remain stable for the solution to be technically viable and economically applicable on a commercial scale.
The most obvious solution to reduce cavitation — simply decreasing the propeller rotations — is not a real option: a commercial ship operates within strict parameters of speed and logistical efficiency, and sailing slower would represent an unacceptable economic impact for operators, shipowners, and global supply chains.
Modest budget, global scale problem
The MinKav Project began in January of this year, will last three years, and has a budget of 390,000 euros, a modest amount considering that the problem it seeks to solve affects tens of thousands of vessels and the marine ecosystems of oceans in all regions of the globe.
Even if the project achieves positive results in the laboratory, there will still be a long road ahead to bridge the gap between the experimental solution and real-world application, which involves testing on commercially sized vessels, validation under different operational conditions, and technical adjustments throughout the process.
The initiative reflects a growing recognition in the maritime sector that acoustic pollution needs to be addressed with the same seriousness as other forms of environmental impact, and that innovations applied to propulsion can significantly contribute to reducing a problem that affects the health of the oceans on a global scale.
Seja o primeiro a reagir!