Reducing Bow Waves on Ships Sailing Through Waterways
When sailing through narrow channels, reducing vessel speed reduces both the size of the bow wave and coastal erosion caused by such waves. There several other methods that promise to reduce the size of vessel bow waves, with potential to reduce both vessel fuel consumption and coastal erosion along navigable waterways.
The submerged cross section of the bow of boats and ships accounts for most of vessel fuel consumption. Forward propulsion involves a transfer of energy that produces as waves on the water surface. Increasing ship speed increases the size of the bow wave and also its fuel consumption. Research focused on reducing the size of the bow wave resulted in the development of the bulbous nose at the bow of modern ships. It reduces the size of the bow wave, changes the wave angle relative to the ship and reduces ship fuel consumption by some five percent.
Bow waves become especially problematic when vessels sail along navigable inland waterways and especially when water levels are extremely high, as when flooding occurs. During periods of extremely high water levels, navigation was actually suspended along a section of the Mississippi River and during early 2017 there was a threat of possible suspension of shipping along a section of the St Lawrence Seaway. Ship generated bow waves have been identified as being the cause of coastal erosion along section sections of the St Lawrence River located between Lake Ontario and Gulf of St Lawrence.
Commerce Along Waterways
Maritime transportation that sails along inland waterways offers the lowest transportation cost in the movement of bulk freight and large numbers (over 100) of containers. It is the reason why bulk carriers and a few container vessels sail along the St Lawrence Seaway, the Mississippi River system, South America’s Parana River, Europe’s barge canal network, China’s inland waterway network, India’s Ganges River and even Egypt’s Suez Canal. Suspending navigation along any of these waterways for reasons of too little water depth or flood water level water depths results in major increases in transportation costs.
During periods of low water levels, cost competitive waterway transportation may still be possible where barges coupled to form an extreme length of train or tow each carry reduced payload. During periods of extremely elevated water levels, barges of specialized hull design and coupled into trains would each carry reduced payload while sailing at reduced speed to reduce the bow wave. Such operation could be viable depending on delay of delivery and especially if the tug moving the tow employs a propeller that delivers its peak efficiency at a low sailing speed.
Hull Design – Twin Hull
The development of the bulbous nose represents a significant step in reducing the size of and energy consumption of ship bow waves. Twin-hull catamaran vessels can offer generous interior volume aimed at carrying low density payloads. Reducing the submerged equivalent bow cross section could generate a much smaller bow wave than mono-hull vessel designs. The twin-hull concept can be designed to include a converging entrance between the two hulls, at the bow, to redirect water to flow through a channel formed between the hulls instead of having a bow wave propagate sideways from the forward sailing vessel.
Installing azipod propulsion near the bow (stern thruster steering) between vessel twin-hulls will enable the propeller to push a stream of water rearward between the hulls, with the vessel bow producing a very small residual bow wave. Research and testing has been under way in the Southern USA on hull designs that redirect the equivalent of the bow wave to pass under the vessel and with minimal residual bow wave. Such a design could carry 80 percent of the payload of a mono-hull vessel and sail through flood levels along navigable waterways and produce minimal coastal erosion along river banks.
Coupled Twin Hull Vessels
Mono-hull barges have for decades between coupled lengthwise and sideways into tows to move freight along inland waterways. There appear to be multiple methods by which to couple twin-hull vessels lengthwise as well as sideways. Parallel lengthwise spring-loaded couplers will need to provide for relative pitching, yawing and rolling motions. A forward propeller installed between the hulls of the bow of the lead vessel, or at the stern of a forward tug couple ahead of it, would generate a backwash that would flow rearward through the channel located between multiple twin hulls.
Extended length, coupled tows of twin-hull could easily sail through the gentle water conditions encountered along inland waterways. In some regions, there may be need to sail vessels along both inland waterways and larger inland lakes, or the combination of a section of ocean and inland waterway. While single vessels could sail through rougher waters, there would be need for further research to develop couplings that would allow lengthwise coupled twin-hull vessels to sail through waters such as the Gulf of St Lawrence, across the Great Lakes or between the Red Sea and Mediterranean Sea via the Suez Canal.
Specialized Tug for Towing
Tugs that use vertical-axis counter-rotating propulsion can be coupled to the bow of large ships for tow and navigation. There may be scope to modify a towing tug to provide towing assistance and navigation to a large vessel while deflecting the bow wave so as to minimize coastal erosion. Wide spaced twin hulls of a catamaran tug may be designed to match the beam of a wide container vessel, with twin propellers mounted between the hulls to operate on each side of the bulbous bow nose of a ship that is being towed or partially towed.
Forward propellers operating on each side of the bulbous nose of a ship bow could convert most of the bow wave to a fast, rearward flowing water stream that will courtesy of the boundary layer effect, will flow mostly along each side of the bow and along the side of the ship. Depending on a decision by the Suez Canal Authority, such a tug may enter service following completion of parallel navigation channels along the Suez Canal. It may become possible for larger vessels that sail with greater draft and greater beam to transit through the canal.
Retractable Bow Propellers
Propellers mounted on each side of the bulbous nose of a ship’s bow could, when activated, push water rearward along the ship’s bow and side while possibly dissipating much of the bow wave and reducing the coastal erosion that such a wave could cause. Depending on the Suez Canal Authority, such propellers could be required to operate to transit a ship of 1,200 cubic meters submerged cross-section through future parallel channels of the Suez Canal. There may be scope to negotiate with the authority to consider increasing vessel cross section and its operating requirements while it transits through the canal.
If the Suez Canal Authority continues to enforce the maximum 1,006 cubic meters submerged cross-section restriction, larger vessels will have to sail via Cape Town and depending on future weather conditions, sail via the Canadian side of Arctic. If the authority establishes terms and requirements for a container ship of 1,200 cubic meters to transit the canal, then maritime designers and ship transport companies will need to decide on how to meet such terms and requirements. One possible future option could involve super transshipment terminals located at each end of the canal, with coupled maritime super trains carrying containers along the canal.
Recent research by McKinsey Consulting suggests larger container ships in the future. Plans are underway to develop separate parallel northbound and southbound navigation channels at the Suez Canal. Such development opens the door to possible discussions with the Suez Canal Authority as to the conditions under which they would consider allowing a ship built to 1,200 cubic meters submerged to transit through the future canal.
Research has been under taken into reducing ship bow waves and includes a hull design that redirects bow wave to pass under the hull, leaving only a residual bow wave of minimal wave height. Such waves inflict minimal erosion along the coasts of navigable waterways. There may be scope to greatly reduce the bow wave of a ship of 1,200 cubic meters of submerged cross section and inquire of the Suez Canal Authority as to their requirements for such a ship to transit through the canal.
The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.