36 Research
Ship Hull Coatings, Optimization, Maintenance and Design What Works The surface roughness of the ship increases over time due to cracking and coating damage, rust and biological fouling. This layer grows in thickness along the sides of the hull, increasing the viscous (frictional) resistance. Monitoring hull coatings to ensure uniform thickness and smoothness is essential. Using divers or automated systems to brush the hull, in order to remove organic buildup and inconsistencies, can significantly reduce resistance. Typically every three to five years, foul-release and anti-fouling coatings are reapplied to achieve correct uniform thickness and smoothness on the hull. The more frequently these can be applied the better. Increasing docking frequency to brush the hull can offer efficiency gains as well. Artificial air-lubrication technologies, including polymers, air bubbles and air cavities, can reduce resistance by more than 5%. Recent discussions have focused on high-potential-efficiency hull coatings based on nanotechnology. Preliminary data suggests this technology can yield approximately 15% reductions in viscous frictional resistance. Finally, ships with small length/beam
ratios (L/B ratios) can be retrofitted with after-body flow-control systems, such as guide vanes, in front of the propeller and wake-equalizing ducts, which increase propulsive performance. Hull practices can be applied to the range of ships and are most effective for tankers and bulk carriers. Ship operators can adopt best management practices to check hull performance, including performance monitoring through data reported from the ship and speed trials.
Monitoring hull
coatings to ensure uniform smoothness is essential
CREATING CLIMATE WEALTH
Propulsion Alternative Propulsion Systems What Works Alternatives to the screw propeller, which integrate the propeller and rudder units, have adopted creative descriptions, such as “duck feet,” “whale tail,” “fish tail,” and “goose feet.” Based on a more complex motion, these systems have the potential to increase efficiency.
Propellers New Propellers, Maintenance and Optimization What Works Efficiency gains are possible by reducing revolutions per minute (RPM) and increasing propeller diameter, such as with fixed-pitch (helical), controllable-pitch (CP), and vertical axis (azipods) propeller options. Fitting new large-diameter propellers on existing ships with smaller diameters can offer an estimated 5-10% efficiency gain. Additionally, devices are available which recover rotational energy in propeller flow and pre-rotation of inflow into the propeller, such as coaxial contra- rotating propellers and free-rotating vane wheels. Relying in part on testing data (many devices are still in the testing phase), the range of efficiency gains for each is typically 1-10%. However, some technologies have demonstrated gains of 15-20%. Propeller maintenance, including polishing and pitch optimization, can decrease fuel consumption by as much as 3%. Scenarios tested include cargo ships, bulk carriers, tankers and container ships.
Engine Recovery systems, Gas-fuelled Engines and Engine Upgrades What Works Engine recovery systems for low- and medium-speed engines, such as Organic Rankine Cycle systems and thermo- efficiency systems, can increase engine power by approximately 10% by reducing heat loss. Payback has been estimated at five years for many of these options. Gas-fuelled engines, particularly natural gas, have shown increases in shaft efficiency of around 6%. These engines have higher exhaust temperatures and therefore higher recovery potential. Engine upgrades can reduce fuel consumption by increasing power output. Upgrades include turbochargers, parts to increase compression ratios, and parts to minimize the loss of combustion efficiency.
Software Weather Routing What Works Cost-efficient software that charts the most appropriate course for a vessel is currently available and can reduce fuel consumption by an estimated 5-10%.
Payback Periods In a review of over 30 new technologies, Carbon War Room estimated that 75% had average paybacks of less than three years. Technologies with some of the shortest payback periods, of under one year, include weather optimization software and advanced paint (ship coating) that reduces friction and offers an estimated 9% fuel saving. Despite the availability of these technologies, uptake has been gradual to date. Other low-hanging fruit with respect to technology upgrades includes plate-heat exchanger optimization and certain configurations of pre- and post-swirl devices. Operational enhancements that have less than one-year payback periods on average, include propeller and hull maintenance, the removal of the turbo changer during slow steaming, and energy management. ||||
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