Bionics and green technology in maritime shipping: an assessment of the effect of Salvinia air-layer hull coatings for drag and fuel reduction

Abstract

To save energy and reduce environmental impacts, new technologies towards a development of a sustainable ‘greener’ economy are needed. The main opportunity to improve sustainability by reducing emissions is within the transport sector. More than 90% of all goods worldwide are transported by ships. Particularly maritime ships using heavy fuel oil and marine gas oil play a major role. The total fuel consumption of shipping in 2016 was about 250 m t (domestic ca. 50 m t, international shipping ca. 200 m t). The vast portion of the energy consumption of a ship is the need to overcome the drag between ship hull and water—depending on the shape of the vessel and its size up to 90% of total fuel consumption. This means reducing drag helps to save fuel and reduces carbon emissions as well as pollution considerably. Different techniques for drag reduction are known, e.g. the micro-bubble technique or the bulbous bow. We investigated a novel bioinspired technique since 2002: the application of biomimetic surfaces with long-term stable air layers on ship hulls, serving as a slip agent. This technology is based on the Salvinia Effect, allowing a permanent stabilization of air layers under water. In this case study, we analysed the possible savings, which also could be combined with modified micro-bubble technologies. We calculated, based on a selection of five ship types, representing 75% of the world fleet, that air-layer hull coatings could lead to estimated savings of 32.5 million tons of fuel (meaning 13.0% of the worldwide shipping fuel consumption), equal to 18.5 billion US$ and 130.0 million tons of CO 2e per year. The positive impacts on global temperature and other greenhouse gases are calculated and could be a contributing factor in accomplishing the UN Sustainable Development Goals and the Paris Agreement to the UN Framework Convention on Climate Change. The study is a contribution to enhance our patchy knowledge concerning the potential economic and ecological benefit of bionics and biomimetic technologies. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology’.

Shaping the Fate of Life on Earth: The Post‐2020 Global Biodiversity Framework

“…Bionics may inter alia either relate directly to biodiversity services or indirectly to fields such as economics and the energy sector (e.g. Busch et al, ). Overviews, a discussion of terminology and the intimate relationship between biodiversity and bionics are given in Barthlott et al (, ).…”

Quo vadis plant biomechanics: Old wine in new bottles or an up‐and‐coming field of modern plant science?

“…Barthlott et al., ), the Salvinia effect (air‐retaining surfaces that reduce friction in vessels inspired, for example, by the leaves of the waterfern Salvinia natans ; cf. Busch et al., ), shape optimization through computer‐aided optimization (CAD) inspired by adaptive tree growth (cf. Mattheck, ), the façade‐shading systems flectofin® and flectofold (inspired by the movement of the perch of the bird‐of‐paradise flower Strelitzia reginae , and the snap‐trapping of the watertrap Aldrovanda vesiculosa , respectively; cf.…”

Air Retention under Water by the Floating Fern Salvinia: The Crucial Role of a Trapped Air Layer as a Pneumatic Spring

“…Superhydrophobic air-retaining surfaces underwater offer a great potential for drag reduction of ship hull coatings or in fluid transportation. [1][2][3][4][5][6] Additionally, they will extend the wide range of applications of superhydrophobic surfaces in the field of water-repellence and self-cleaning [7][8][9][10][11][12][13][14][15][16][17] as it was recently shown by measuring the friction reduction [18][19][20][21][22][23][24] or the slip length of the hydrodynamic velocity profile as a corresponding quantity. [4,[25][26][27][28][29] However, for any technical application of underwater air layers, the long-term stability (persistence) of the air layer is of vital importance.…”

“…Therefore, the surface of Salvinia leaves is considered as a biological model for technological air-retaining surfaces. [5,[40][41][42][43][44][45][46][47][48][49] In order to have an effective air retention, the upper side of the leaves is covered with elastic, superhydrophobic, eggbeater-shaped trichomes (later called "hairs") (see Figure 1a,b). The backside of the leaf is hydrophilic, and therefore staying in permanent direct contact with water.…”