Southwest Marine Yard Repowering San Francisco Commuter Ferries With Detroit Diesel Allison Engines

New diesel engines in three of San Francisco's commuter ferries are expected to save their owner, the Golden Gate Bridge, Highway and Transportation District, more than a quarter-million dollars a year in fuel costs. A pair of fuel-efficient Detroit Diesel Allison 16V-149TIB engines are replacing the three gas turbines that were installed in each of the 725-passenger vessels when they were built in the mid-1970s.

The repowering is being done by Southwest Marine, Inc. of San Diego.

The San Francisco, first of the three ferries to be repowered, has been in service for several months.

Even during her break-in period, Ferry Division manager Eric Robinson has found "dramatically improved performance" from the repowered boat, leading to a savings in commute time as well as impressive dollar savings. These savings are being achieved despite a reduction of propulsion power from 7,500 shp with the original gas turbines to 3,100 bhp with the new diesels. Reliability has been 100 percent, and the noise level has been as low as it was with the gas turbines.

The economies gained from the repowering program will show up in expanded service of the ferries, which were built to relieve commuter congestion on the Golden Gate Bridge. When all three boats are back in service, Mr. Robinson expects ridership to increase by 40 percent over previous levels, further adding to the economic viability of the Ferry Division. He also notes a 60-percent reduction in fuel consumption during the first threemonth operation of the San Francisco.

The three ferries—San Francisco, Marin, and Sonoma—provide passenger- only commuter service between the Ferry Building terminal close to downtown San Francisco and the port of Larkspur serving the residential communities of Marin County. Passengers travel in luxury during the 45-minute crossing, with beverage service and intercom music throughout the enclosed, multideck boats.

Fuel savings have already met the goals set for the repowering, and overall performance has exceeded expectations. Hourly full-power fuel consumption has averaged 170 gallons with the two diesels and one genset; the original gas turbines burned 500 gallons an hour. Cruising speed has met the boat's design speed of 20.2 knots—surprising in view of the great reduction in horsepower.

A critical demand has been that ferry service be increased to meet anticipated ridership, and that the Division's high level of on-time ferry departures and landings be maintained.

The markedly improved performance of the boat at slow and intermediate speeds, the result of conversion from waterjet to propeller propulsion, is already paying off in terms of time saved during docking and departures, and has added an important margin of safety to ferry operation.

In order to convert from the waterjets to propellers, a five-foot "bustle" is added to the stern of each ferry to house rudders and steering mechanism. This slight increase in the waterline length of the 165-foot boats has contributed to maintaining the original design speed.

Repowering of the second and third boats is continuing, with the Marin and Sonoma expected to be in service by the end of this year.

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Maritime Reporter Magazine, page 104, Jun 1985

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