Looking For Answers To Wake And Emission Questions As High-Speed Ferries Solve Traffic Congestion Problems

By, Wes Starratt, PE, Senior Editor

Long ago, we learned that for every goal there is a price to be paid and that every
achievement creates problems that must be solved. In the case of high-speed catamarans, two of the major problems are shoreline erosion caused by vessel wake and diesel emissions.

The Washington State Wake Problem

Washington State Ferries, with its 29-boat fleet, is the largest ferry system in the United States. For many years it has operated slow automobile/passenger ferries between Bremerton and the City of Seattle. But, as the number of commuters grew, the demand for high-speed passenger ferries increased, and Dakota Creek Industries of Anacortes, Washington, was commissioned to build two high-speed catamarans for the service: the 143-ft, 350 passenger Chinook in 1998 and her sister ship, the Snohomish, in 1999. Each had two diesel engines powering water jets to achieve a speed of 38 knots (almost 44 miles per hour). Commute time was reduced to 30 minutes, and the passengers were happy.

With twin hulls and low draft, these boats create much less wake than comparable single-hull vessels, but with the high levels of energy generated from the higher speeds, wake proved to be a surprisingly significant problem in certain areas.

Between Bremerton and Seattle, there is a 2 ½ mile long, relatively shallow and narrow strait of water called Rich Passage. There, waterfront property owners were not happy because the ferries were causing erosion along the shoreline. Washington State Ferries slowed its boats through the passage and, at the same time, instituted a study that showed no erosion in areas where there are natural beaches, but erosion only where the shore has been armored by bulkheads. Nevertheless, legal action by property owners brought the matter to a head, resulting in a permanent reduction of the speed of the ferries through Rich Passage and an increase of the commute time from 30 to 40 minutes (still better than the 65 minutes the auto ferry takes). Now the property owners are happy, but the commuters are not as happy as they once were.

Reduced speed appears to have provided an immediate answer to the problem, but, for long term solutions, marine architects have gone back to their drawing boards. Longer, more slender hulls, perhaps made of lightweight composites may reduce the problem in future high-speed ferry designs.

Critical Wake Problems in Venice Lead to Low Emission Propulsion Systems

For many years it has been claimed that glorious Venice is slowly sinking into the sea. That may be the case, but, astute eyes have also pointed to the critical erosion of building foundations along the canals as a major problem. Some have said, that "we will have to wait until one of our palazzi comes crashing into a canal before we do something about the critical wake problems created by the multitude of boats on our canals." Among the boats are more than 100 vessels of 180-210 passenger capacity for public transport. Hardly high-speed ferries, these water buses travel at speeds not exceeding 10 knots. But, their number and frequency and the number of privately-operated boats on the canals are creating a major wake problem on the canals of Venice.

So, two years ago, a group of Italian, Dutch, and German organizations got together to establish the LIUTO (Low Impact Urban Transport water Omnibus) project to develop a prototype boat for public urban transport. The primary objective was to reduce wave and wash generation by improved hull design and the use of lightweight composite materials. Reduced diesel emissions have also been achieved.

The twin-propeller propulsion system developed for the prototype boat is operated by two electric motors powered by battery packs that are, in turn, charged by a diesel generator running at a constant speed. Low fuel consumption and, at the same time, low emissions are achieved by the operation of the diesel engines at a single optimum efficiency level. Such hybrid diesel-electric power systems, although more costly to build, might find use in our high-speed ferries because of their fuel efficiency and low diesel emissions.

Solving Emission Problems by Fuel Cells and Other Means

While considerable development is taking place to increase the efficiency and decrease the emission of diesel engines, considerable effort is being made to develop other low- emission propulsion systems for ferries, including turbines operated on natural gas or hydrogen and hydrogen fuel cells.

But, fuel cells are not new. The idea of combining hydrogen and oxygen to produce electricity and a harmless emission in the form of water goes back over one hundred years. However, the technology didn’t catch on until NASA started using modern fuel-cell units to power spacecraft and provide drinking water for astronauts.

The idea of using fuel cells to power boats and ferries is just beginning to dawn, and early in October, the first fuel-cell-operated water taxi was demonstrated on San Francisco Bay by DCH Technology, Inc. Only 18 ft long and capable of carrying up to nine passengers at a speed of 5 knots, the water taxi would be capable of providing services in calm water such as the Oakland Estuary, Lake Tahoe, or Newport Beach Harbor where it has already been tried out. Since the boat doesn’t have a name, let’s call it Heidi in honor of Water Transit Authority’s Heidi Machen.

Heidi’s 1-kw hydrogen fuel-cell generates electricity that charges batteries that, in turn, provide power to the boat’s 10-hp outboard electric motor. The hydrogen used to power the fuel cell is contained in two compressed hydrogen tanks.

Funding for Heidi’s demonstration was provided by the Air Resources Board of the California Environmental Protection Agency, which stated that the purpose of the program is "to execute a low cost maritime hydrogen transportation program in parallel with the State of California’s efforts to promote hydrogen and fuel cell technologies in the automobile industry. The agency’s executive officer, Michael P. Kenny, stated that, "We believe that the best interests of the State of California will be served by having the State fund DCH’s conversion of the Hydrogen Water Taxi to a hybrid fuel cell powered design, whereby the environmental benefits of zero emission hydrogen fuel would be mated with the superior operating efficiencies of a DCH fuel cell power plant.

"The numerous coastal and inland waterways of the state are popular places for a large and growing number of electric powered motor craft. These electric powered vessels are, like most electric vehicles, limited in range by the storage capacity of their batteries. DCH therefore decided … to extend the operating range of such watercraft by using a small on-board fuel cell to recharge the boat’s batteries in a quiet and environmentally friendly manner. Examples of where this technology can be used in the near term are abundant. Newport Beach Harbor, for example, is the home of over 1,000 electric powered recreational watercraft."

Today it’s a nine-passenger water taxi, perhaps someday fuel-cell technology may advance to the point where it will be capable of powering larger boats in an environmentally friendly manner. Meantime, further progress can be expected in reducing the wake created by high-speed catamarans and by improved diesel engine technology. Yes, progress is being made on two key environmental issues involving the development of a regional ferry system on San Francisco Bay. 

Working Waterfront

High Speed Ferries Answer Congestion Problems