Rising oil prices and environmental concerns are driving boat development towards better fuel efficiency and reduced pollution. Global warming impact of shipping also begins to be of concern. According to Professor James J. Corbett of the University of Delaware, 20-30% GHG-emissions reduction for shipping is possible as well as economical and health benefits[1]
Possible ways to achieve this include reducing drag losses and augmenting fossil fuels by more environmentally friendly sources of energy.
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New technologies can offer significant advantage in fuel efficiency by reducing drag. For instance modern materials like aluminum alloys or carbon-fiber composites reduce hull weight and hence displacement and drag for a given payload.
Bulbous bow is a protruding bulb at the bow (or front) of a ship just below the waterline that modifies the way the water flows around the hull. Large ships with bulbous bows generally have a twelve to fifteen percent better fuel efficiency than similar vessels without them.[2]
Surface effect ship reduce drag by reducing wetted area of the hull. In Skjold class patrol boats this is achieved by augementing buoyancy by a fan-blown skirted compartment between the two rigid catamaran-type hulls. This permits to lower displacement and hence reduce drag at high speed.
A related concept is Air Cavity System (also available as upgrade for existing vessels[3]). By creating an air cavity on the underside of the hull it claims to reduce drag by up to 15%.[4]
Wind power as a free, clean and renewable source of energy has been used to propel watercraft since prehistoric times. Classic sails are however poorly suited for modern economic conditions not only because of inherent dependence on weather, but also because of large crew requirements with associated costs. Some designs try to overcome this issue through the use of modern technologies.
An example for straightforward approach is the windmill ship that captures wind energy with rotor to drive a conventional propeller.
The commercially offered SkySails propulsion system consists of a large foil kite, an electronic control system for the kite and an automatic system to retract it. The kites, having an area of around 320 square meters (3,400 sq ft), can be flown at altitudes of 100–300 meters (330–980 ft). Because of the stronger winds at these heights, they receive a substantially higher thrust per unit area than conventional mast-mounted sails. A ship equipped with the current SkySails could consume from 10 to 35% less fuel.[5]
A number of designs and proposals for Flettner ships exist, however it never demonstrated efficiency to be economically viable. Improvement has been attempted by Jacques Cousteau who designed Turbosail. Unlike simple Flettner rotors, it is able to produce thrust in the direction of travel, regardless of wind direction. The first turbosail-equipped ship, Alcyone, reported a 1/3 fuel savings. The efficiency of the system has however not been subjected to sufficient comparative engineering research. There have been only two turbosail-equipped vessels on which active research has been performed.
Fuel cell powered boats might benefit from higher thermodynamic efficiency of fuel cells compared to internal combustion engines (40-60% vs 20-25%). Greatest impediment is currently high cost of fuel cells. In 2009, the Department of Energy reported that 80-kW automotive fuel cell system costs in volume production (projected to 500,000 units per year) are US$61 per kilowatt.[6]
Solar panels have been also suggested for powering primary and secondary ship systems [7][8]. Solar powered boats have mainly been limited to rivers and canals, but in 2007 an experimental 14m catamaran, the Sun21 sailed the Atlantic from Seville to Miami, and from there to New York.[9]