At the recent International Tug & Salvage Conference in Vancouver details of a new hybrid tug was presented with the triple propulsion modes of diesel electric, battery and fuel cell claiming to give a 67 per cent emission savings over conventional diesel operation. Aim of this particular Hybrid Electric Tug design is to provide an operating mode of zero emissions for the majority of the tug's duty profile during low power operation up to 35 per cent of full power: this includes transits at a cruising speed of about nine knots. Based on a current conventional 24-m hull design developed by Capilano Maritime Design Ltd. with 55-tonne bollard pull, a more powerful 70-tonnes bollard pull version would only require minor changes to the hull and propulsion drives with an increase in battery capacity with diesel generator and fuel cell systems remaining unchanged. Four fuel cells of the PEM type are specified giving a total continuous power output of 600kWe, representing 17 per cent of power. There is a 1,000 kW-h capacity Li-Ion battery system which allows a combined power output of 1,250 kWe. A storage capacity of 1,200 kg of hydrogen provides an endurance of about 40 hours at full power, sufficient to allow refueling intervals of about once per week.
At the recent International Tug & Salvage Conference in Vancouver details of a new hybrid tug was presented with the triple propulsion modes of diesel electric, battery and fuel cell claiming to give a 67 per cent emission savings over conventional diesel operation. The usage profile of harbour / ship docking tugs is an ideal candidate for hybrid applications as the main diesel engines are not needed for 80 per cent of the time.
The aim of this particular Hybrid Electric Tug design is to provide an operating mode of zero emissions for the majority of the tug's duty profile during low power operation up to 35 per cent of full power: this includes transits at a cruising speed of about nine (9) knots.
The proposed vessel is based on a current conventional 24-m hull design developed by Capilano
Maritime Design Ltd. with 55-tonne bollard pull, capable of handling most ship-docking duties in a modern harbor. A more powerful 70-tonnes bollard pull version would only require minor changes to the hull and propulsion drives with an increase in battery capacity. The diesel generator and fuel cell systems could remain the same.
Four fuel cells of the PEM type are specified giving a total continuous power output of 600kWe, representing 17 per cent of power. Although the fuel cells are conservatively rated at 150 kWe, practice shows that where fuel cells are employed in a hybrid combination with batteries in a marine application with excellent seawater cooling, the maximum rating may be increased to nearly 200 kWe.
There is a 1,000 kW-h capacity Li-Ion battery system which allows a combined power output of 1,250 kWe, or 35 per cent of power for more than one hour. A major benefit of the large capacity battery system is that it permits onboard storage of usually less expensive energy purchased from a shore power supply.
A storage capacity of 1,200 kg of hydrogen was specified to provide an endurance of about 40 hours at full power, sufficient to allow refuelling intervals of about once per week.
The capital cost for a conventional tug is approximately $12M, in comparison the cost of this proposed vessel is $23-25M, however if several are built the cost could be expected to reduced to $16-18M due to a significant price reduction of the fuel cells and advanced batteries.
On the question of life cycle costs, it is estimated that the Hybrid Electric Tug will be lower, depending on future rates for diesel fuel and shore power.