With introduction of various constructional, technical and operational/navigational methods a large container vessel operating at 16-20 knots of speed can save 20-25% fuel, bringing down the operating cost burden to owners by 5-10000USD per day. Below are the methods which are in use singularly or in combination to maximise the fuel savings and minimise the operating cost of the vessel;
Fore body optimization by redesigning bow – Bulbs are most effective at certain Froude number (speed-length ratio) and draft. Changes in speed and draft significantly change the wave created, such that reductions in draft or speed can actually lead to increases in wavemaking resistance. As few commercial vessels operate solely at a design draft, compromises in the bulb design are needed to provide good performance over the expected range of operating drafts and speeds. It provides more favourable performance over the anticipated operating profile of drafts and ship speeds. Estimated fuel saving 5%.
Old bow -Bulb shape earlier designed to suit design draft and speed.
New Cylindrical shape bow – to suit expected range of operating design draft and speed. Estimated new steel 120MT
Propeller efficiency upgrades – The propeller’s efficiency, amongst other parameters, is an important consideration for achieving economic sailing. Fouling, surface roughening and leading edge damage to the propeller, when in service, can result in efficiency losses of 3-7%. Also, by replacing outdated existing propellers with new ones designed based on the latest knowledge, propeller designs and operating profile of the vessel, significant savings with short payback periods can be achieved. The new Wärtsilä OPTI propeller, Mitsubishi and MMG retrofit new propellers are very suitable on this respect.
Old 6 bladed 80tons weight propeller been replaced by 5 bladed 60 tons OPTI design propeller.
Propeller boss cap fin – Wärtsilä (EnergoproFin), MMG (EPF), Mitsubishi (PBCF, first proposed in 1987) are few manufacturers of propeller cap fin, it is fitted in place of propeller cap to increase the propulsion efficiency and decrease power demand by propeller to generate same thrust.
Energopac rudders and HR nozzles that can also be retrofitted to improve the flow characteristic hence increase in propulsion efficiency.
Main Propulsion Turbochargers – Vessel fitted with 2 or more turbochargers can have one turbo charger cut off at low load operation to optimise the scavenge air pressure. Other method is variable geometry turbochargers, which contributes in better efficiency of turbocharger, thus better combustion, better power thus saving in engine performance and fuel.
Tutbocharger cut off device.
RTA injection timing automation (RITA) – how it works? Pressure in the cylinders is monitored by three pressure transducers mounted on the cylinder head just below the indication cocks; alternatively a direct connection to the ICM product is also available. The sensor signals are then sent to the control cabinet. The optimal set-point is calculated according to present load and ambient conditions. Corrective signals are then sent to the engine’s variable injection timing (VIT) system that adjusts the cylinder pressures accordingly. 1.5% reduction fuel consumption can be achieved with this system. First installation on an RTA96C engine offering a solution that automatically controls the adjustment of injection timing based on cylinder pressure reduction of fuel consumption by 1.5%, leading to savings on the fuel bill, reduced operating costs, optimal engine operation within design criteria and reduced CO2 emissions.
Variable base number cylinder lubrication – this system offers refreshing of main engine system oil, thus providing less friction of running parts, better efficiency and fuel saving in turn.
Water injection in fuel – At 30000KW actual load, around 120MT/day fuel consumption, vessel will require 20 MT water/day and gives fuel saving of about 5-7% as a result of combustion. LEMAG Slashpol E WiF is one of the system used on board.
Energy efficiency during service.
Trim Optimisation – Measuring actual performance (fuel consumption, power and speed) and the corresponding draft and trim while underway provides data that can be used to generate optimum trim tables. 1 to 2 percent reduction in propulsion fuel consumption can be achieved.
Autopilot improvement – The operator can make simple adjustments in existing linear autopilots (~zero cost). Cost for fully adaptive autopilot, useful for heavy weather conditions or directionally unstable ships.
Slow steaming.- As per calculation speed reduced by 10% – power demand reduces by 27 percent – fuel consumption for the voyage reduces by 19 percent.
Weather routing – Choosing a safe and energy efficiency route.
Hull and propeller efficiency management – Biological roughness (fouling) also has a significant impact on resistance, even at the micro level. A heavy slime results in a total increase on the order of 15 to 18 percent. Small barnacles and weeds push this up to a 20 to 30 percent increase in total resistance. Good quality foul release coating should be applied during drydocking.
Propeller cleaning between drydocks – polishing a very rough blade (with average surface roughness greater than 30 μm, (Grade F) can lead to a 6 percent reduction in fuel consumption.
Overall energy efficiency management – Continuous planning, Planning, Implementation, Monitoring, self-evaluation and improvement as per new Ship Energy Efficiency Management Plan (SEEMP) adopted in July 2011.
1. ABS SHIP ENERGY EFFICIENCY MEASURES ADVISORY,
2. Wartsila service reference Hamburg -Sud
3. LEMAG Slashpol