Tier 2 to Tier 4 — In One Step (Source: WWW.DIESELGASTURBINE.COM)
Anyone building a ferryboat to operate in the state of California, U.S.A., had better be prepared to make low emissions the leading design criteria. And for a series of ferryboats for the San Francisco, California bay area Water Emergency Transportation Authority (WETA), add low draft, minimal wake and even whale-seeking sonar. The contract with the two shipyards responsible for building this particular series of passenger ferries emphasized emissions — emissions standards far below what is now required in California.

Gemini on sea

The specification called for emissions 85% below 2007 EPA Tier 2 standards, or more than 10 times lower than any other ferry in California. Builders of the ferries for WETA are Nichols Brothers Boat Builders of Freeland, Washington, U.S.A., and Kvichak Industries of Seattle, Washington.

There are four boats in the series, two that are 36 m Subchapter T boats and carry 149 passengers and two that will be elevated to U.S. Coast Guard Subchapter K status (structural fire protection) and carry 199 passengers.

Nichols was the lead builder on the first vessel, Gemini. Kvichak built and outfitted the hulls, installed the engines, gen-sets and other machinery along with the main deck and towed them to Nichols for outfitting. Nichols did the engineering and had the job of designing the tightly specified emission system, however, for specialized assistance with this system, they turned to Pacific Power Products of Kent, Washington, the local MTU/Detroit Diesel distributor.

The emissions challenge was to go from Tier 2 to Tier 4 emissions all in one step. “To meet these tight emission standards, the engines had to use selective catalytic reduction or SCR,” said
Bill Mossey of Pacific Power Products. “Weight, size, installation restrictions and aftertreatment efficiency were all elements in the evaluation, the final outcome requiring a custom-designed solution. Cost was certainly an element, since the emission system came
in at US$1 million, or nearly 13% of the US$8 million price tag for the boat, but to get to the emissions numbers, SCR had to be used,” Mossey added.

The best reactant in such a system is ammonia and the only safe source of ammonia for use in transportation is urea. When heated, urea yields ammonia and cyanuric acid. Cyanuric acid
and water yield more ammonia and carbon dioxide. Adding urea with engine exhaust (which includes nitrogen oxides, or NOx) in a mixing duct, yields ammonia and NOx that is fed into a catalyst reactor where the NOx is removed. A 32.5% urea solution is used in the mixing duct and directed through 12 catalyst monoliths totaling 170 L, arranged in two rows of six along a central plenum, which breaks down the NOx, particulate matter (PM) and carbon monoxide (CO), dramatically lowering emissions. The catalyst is a fiber-reinforced corrugated ceramic material.

In the past, the use of an SCR system in a marine environment caused problems because the catalysts were brick, and those units would tend to develop problems due to vibration and saltwater intrusion. Having the exhaust come out of the stack solved that problem, and the catalyst no longer is based on a brick design.

To validate the design, Nichols built the piping and Pacific Power built a full-size mock-up of the emissions system. Such a full-scale test was necessary because the penalty for not meeting the emission standards was rejection of the vessel. “PM and CO at the 85% test point were well within Tier 2 limits without the SCR system. The SCR system further reduced the NOx emissions by 95%, PM emissions by 53% and CO emissions by 83%,” said Mossey. “We also went back after the first vessel had been operating for six months to evaluate the emissions system and confirm
emissions were still within the WETA requirement,” Mossey added.

The propulsion package was not complicated by requirements for very high speed. WETA wanted a speed of 25 knots, certainly obtainable with the propulsion package consisting of a pair of MTU 16V2000 M71 diesels working with ZF transmissions and 117 cm Michigan propellers, all very conventionaldrivetrain components.

MTU 16V2000 M71 diesel engine

Main engine mounting is another distinct feature of these catamarans. The engines are resiliently mounted on an “I” rail so the engines can be moved aft to be located under a soft patch. “This design allows for engine haul-out without dry docking the vessel,” said Marine Engineering Manager for WETA, Mary Culnane.

The generators are a pair of Northern Lights 65 kW units with auto-start capabilities. A pair of solar panels has been installed to evaluate the feasibility of using this as a power source.
However, another environmental specification called for overall draft at the tips of the propellers to be no more than 1.9 m. This restriction meant that vessel designer Incat Crowther had to create a tunnel in each hull, allowing the propellers to be raised to meet the draft restrictions. Also, aft-mounted adjustable interceptors were used instead of trim tabs. While not having the maximum lift of trim tabs, interceptors interceptors offer reduced fabrication, operation and maintenance costs because of simpler design and reduced hydraulic power requirements.

The bow of the ferry was built with a knife edge to reduce wake, but the port hull was somewhat compromised with the addition of a sonar unit to warn the pilot of nearby whales, logs or other
possible obstructions.

Building this technologically advanced and environmentally compliant ferry was one thing, but getting luxury car-conscious Californians to ride it was another. “In other words, the ferries had to have upscale interiors, roomy seats and what are now standard hookups for laptop computer chargers as well as free wireless access,” Culnane added.

Passenger entrance and exit is via port and starboard doors. WETA is encouraging riders to travel to the ferry terminal via bicycles and has storage for 18 forward and 16 aft on the boat.
Both of the first two vessels, Gemini and Pisces, have been delivered and are working. The two vessels can each accommodate 122 passengers in the main deck cabin and 28 on the upper
deck. The third vessel will be delivered in the fourth quarter 2009 and the fourth is expected to be delivered in spring 2010.

A flow diagram showing the operation of the SCR emission control system
A flow diagram showing the operation of the SCR emission control system

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