Ships could capture energy from waves by imitating whales
In an effort to reduce the environmental impact of commercial ships, a group of U.K. researchers has scoured through the research into a unique technology that imitates the action of a whale’s tail to help propel ships and reduce fuel consumption.
The findings of the review-study from Cranfield University, published in the journal Renewable and Sustainable Energy Reviews in September, found a system of flapping foils can effectively harness wave energy and generate thrust.
About 50,000 merchant ships cross our oceans carrying most of the trade goods between countries every year. And while ships are the most efficient way to move cargo, they contribute roughly three per cent of the total global fossil fuel emissions, according to the International Maritime Organization.
The shipping industry aims to cut emissions by at least 70 per cent by 2040 and to achieve net-zero greenhouse gas emissions by around 2050 through a number of different measures, including increasing fuel or energy source efficiencies and developing alternative propulsion systems that go beyond the conventional propeller.
One of the more innovative potential technical solutions is to equip ships with the equivalent of a whale tail.
As a sailor, I have had the privilege of encountering whales, dolphins and porpoise off the bow of my boat.
It is a magical experience witnessing the smaller animals darting through the water like torpedoes, occasionally leaping above the surface as they gallop through the water.
Larger whales such as humpbacks and the fin whale lazily glide along powered by the slow undulations of their giant tails.
The highly efficient swimming of some marine mammals and fish involves more than simply pushing against the water with their tails to move forward.
Studies in fluid dynamics show that fish get an extra boost from vortices, or whirlpools of water, that form on opposite sides of fish and slide back toward the tail. These masses are thrown backwards producing an opposite reaction of forward thrust.
The new U.K. review study looked at more than 100 years of research that used theoretical methods, computational simulations and experimentation with scale-model-sized ships and full-scale prototypes to imitate nature’s propulsion system and apply it to ships.
Experiments have shown that flapping foils, a technology known as wave devouring propulsion, can capture the free energy of waves and propel ships forward.
The foils are in the shape of broad airplane wings that seem to work best when mounted on the bow — or the front — of a ship below the waterline, essentially putting the tail before the whale.
Ordinarily, as a ship heads into waves, the bow pitches up and down, a motion that passengers and crew often find uncomfortable.
The foil would not only reduce that pitching motion, but thanks to a spring-activated device that moves the foil up and down in sync with the wave, it captures some of the energy in the moving water and turns it into propulsion.
Large waves are a hindrance to ships, slowing their progress and causing them to burn more fuel. But experiments with models and a few commercial products have shown that flapping foils could enable a ship to literally swim through waves, providing approximately 10 to 50 per cent of the propulsive force in certain conditions.
The foils are much quieter than propellers when they’re operating, which can also reduce noise pollution in the ocean that negatively affects sea life.
Similar flapping foil technology could also be used on floating platforms such as oil rigs or offshore wind turbines to assist in station keeping, or holding their position against wind and ocean currents.
After millions of years of evolution, nature has perfected the efficiency of flapping tails, making it look like a simple form of propulsion, but the researchers point out that turning a whale tail into efficient ship propulsion is not that simple.
More work is needed to understand the durability of foils in the harsh marine environment, interactions between the foil and hull of the ship, how many foils would be ideal for each ship and of course the economics of transitioning to wave devouring propulsion systems.
Wave devouring propulsion is just one of many technologies proposed to reduce pollution from shipping. Slower running speeds, switching to cleaner fuels, improved hull coatings to reduce drag and even the use of large kites to pull ships forward are all attempts by the shipping industry to reduce its global impact on our changing climate.
