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An engine of 15MW to 17MW many provide propulsive power to a container ship of 25,000-metric tons dead-weight. However, when it sails at a speed of 20-knots in relatively calm wind, wind resistance may only account for about 1MW to 1.5MW of power. Water drag would account for the rest of the engine power. The bow waves of ships that sail along narrow navigable waterways invariably cause erosion along the riverbanks, doing the work of an excavator. In some cases it may be possible to install boulders and rocks along the riverbanks as a means of reducing erosion.
While there has been much research and development into various ocean wave conversion technologies, there may be scope to extend that research and development to include ship generated bow waves that occur along the numerous navigable narrow waterways around the world. The research may focus on the narrow sections of busy waterways with high-frequency sailings that would include sections of the Panama Canal and of the St Lawrence River. Such technology could convert 70% to 80% of the bow wave energy to electrical power while allowing ships to sail at higher speed along a selected waterway, perhaps enhancing its viability.
The Panama Canal is being upgraded to allow passage to a new generation of wider, longer ships with deeper draft. There are tentative plans to modify the Lower St Lawrence River between the Gulf of St Lawrence and the Port of Montreal to allow the larger vessels access to a new terminal at Montreal. The St Lawrence River is home to several hydroelectric power dams as well as a series of navigation locks that can allow ocean-going ships to access inland ports at Chicago, Milwaukee and Toronto. Water levels have also been dropping in the Great Lakes, requiring that modifications be made along the Lower St Lawrence River to economizing on river water while sustaining marine operations and hydroelectric power generation.
There is historical information that indicates that river levels at Montreal were some 6-feet higher a century ago. It is possible to restrict water flow volumes by at several narrow sections along the St Lawrence River, downstream of Montreal. One option would be to submerge boulders on to areas of the riverbed that outside of the navigation lanes, to reduce overall channel cross sectional area. There is also the option of installing submerged water gates at the narrow sections of channel. Changing ballast would lower the gates when ships approach and raise the gates after a ship has sailed through.
It is also possible to submerge inflatable giant bags on to the channel floor downstream of Quebec City and pump water into them, to simultaneously reduce channel cross-sectional area at that location as well as navigation depth from over 100-feet to that of the new-generation container ships that will sail through. A reduction in channel cross section at strategic points along the river would reduce overall water volume flow rate and achieve 2-objectives: reduce water loss from the Great Lakes and assure large ships passage between Montreal and the Gulf of St Lawrence.
The larger, heavier ships will include greater draft and have increased propensity to generate bow waves as they sail along the St Lawrence River. Those waves may represent some 20MW of power. A technology that could float on the river may simultaneously demarcate the navigation channels and absorb energy from the ship bow wave. Perhaps it may pump water through a flexible pipe over a distance of several miles to a mechanism that drives an electrical generator. The frequency of ships that sail along the waterway would contribute to the viability of the technology.
Bow wave erosion is at its worst along the narrowest sections of the St Lawrence River. These are the very locations where the installation of a water wave energy conversion technology could serve the simultaneous objective of saving whatever remains of the riverbanks while generating multiple short bursts of electrical power that may be transferred into storage, such as flywheels. The challenge for ocean water research personnel would be to develop a viable wave conversion technology that may be installed along shipping channels, at narrow sections of navigable waterways.
A 30,000-tonne ship traveling through a narrow channel at 20-knots may need 18MW of engine power to drive a propeller that operates at 84% efficiency and transfer some 15MW into the river channel as wave energy. Wave conversion technology installed for some 5-miles along both sides of the ship navigation channel could capture some 9MW over a period of some 12-minutes, yielding some 1800kW-hr of power. A frequency of 2-ships per hour could provide some 3600kW-hr of power to a nearby community and a series of 3 x narrow sections of channel could contribute some 10MW-hr of power to the local grid.
There would be potential to install wave conversion technology at 3-locations of the Lower St Lawrence River to the east of Montreal as well as several sections of the Upper St Lawrence River between Montreal and Lake Ontario. It may also be possible to install such technology along the sections of channel at Detroit -- Windsor, at the Strait of Mackinac and at Port Huron -- Sarnia. Such technology may be able to generate viable power along several narrow sections of the upgraded Panama Canal, the Dardenelles channel between the Sea of Mamora and the Aegean Sea, as well as along sections of the Suez Canal. While the cost of reinforcing riverbanks against erosion from ship bow waves may be high, there may be scope to undertake viable installation of energy conversion technology along narrow sections of navigable waterways.
