Final engineering model of the SF-BREEZE as designed by Elliott Bay Design Group. The top deck holds the LH2 storage tank, the associated vent stack, evaporation equipment, and the Pilot House of the vessel. The main deck holds the PEM fuel cell power racks and the passenger compartment. Click to enlarge.

In the course of the study, we examined over 10 major issues where feasibility was initially unknown. SF-BREEZE sailed through them all.

—Lennie Klebanoff, Sandia co-author of the SF-Breeze study

Tom Escher, president of San Francisco’s Red and White Fleet, first conceived of the project when he asked if it was possible to do away with emissions altogether on one of his ferries.

This is a game changer. We can eliminate environmental pollution from ships. This could have a major impact on every shipyard in the country.

—Tom Escher

Hydrogen-powered ferries do exist, but most are smaller, slower vessels used for tours on lakes and rivers. The SF-BREEZE study set out to discover whether it is technically feasible to build a large, fast vessel; could meet maritime regulations; and could be economically competitive with modes of transportation already available in the San Francisco Bay area.

The group drew up conceptual specifications: a 150-passenger commuter ferry that would travel four 50-mile round-trip routes each day at a top speed of 35 knots (~39 mph) about 60% of the time. The ferry could refuel midday, between the morning and afternoon commutes.

The project team split into two branches. One focused on technical and regulatory feasibility of the high-speed ferry, the other on the feasibility of the required land-side refueling infrastructure.

Through examination of the options, the project team selected proton exchange membrane (PEM) fuel cells for the powerplant due to their low weight and volume, commercial availability, proven track record, zero emission characteristic, and acceptable power performance. The fuel cell base model chosen for this case study was the Hydrogenics HyPM HD30. Liquid hydrogen (LH₂) was selected for on-board storage in order to minimize the weight that is so critical for performance of a high-speed vessel.

The final specifications for the SF-BREEZE were:

• Passenger capacity: 150 (the maximum allowed by Subchapter T regulations).

• Top Speed: 35 knots.

• Total installed power: 4.92 MW (4.4 MW for propulsion at top speed, 120 kW for auxiliary power, and the remainder for margin) consisting of (41) 120 kW PEM fuel cell racks, each rack containing four 30 kW PEM fuel cell stacks.

• Fuel: 1,200 kg (~4,500 gallons) of LH₂ contained in a single Type C (pressurized vessel) storage tank on the top deck, enough for two 50 nm round trips before refueling, with 200-400 kg margin.

• Electrical architecture: DC power from the fuel cells converted to AC power for the motors. Either one or two motors per shaft.

• Propulsors: Waterjet or Voith linear jet.

• Amenities: Standard passenger cabin with restroom and snack bar.

• Zero greenhouse gas and criteria pollutants during operation.

Due to the difference in characteristics between diesel engines and PEM fuel cells, the SF-BREEZE would have the following benefits in addition to its elimination of emissions:

• Superior response time during power changes (such as during maneuvering).

• Less noise and vibration on-board.

• Elimination of diesel fuel spills, diesel odor, and exhaust odor.

This kind of boat has never been built before. Hydrogen fuel cells are heavier than diesel engines for a given power output, so achieving the right power-to-weight ratio for the vessel was tricky.

—Curt Leffers, the project manager for Elliott Bay Design Group

The need for speed drove the design to a slightly longer catamaran. The engineers were able to save weight by consolidating the support equipment for the fuel cells.

To achieve the necessary safety standoffs from the fuel cells, the designers placed the fuel cells on the main deck of the vessel in a separate compartment. Leffers explained that this provides physical separation between the fuel cells and passengers.

Emissions. The project team investigated the SF-BREEZE GHG emissions associated with five LH₂ fuel production pathways including renewable and non-renewable (fossil-fuel based) methods. While hydrogen PEM fuel cell technology has zero emissions at the point of use, it is important to consider the fuel production pathway and delivery emissions in a “well-to-waves” (WTW) analysis. The team found that the WTW GHG emissions for the SF-BREEZE using non-renewable LH₂ are significantly higher than for the diesel-fueled Vallejo ferry on a per passenger basis.

Due to the higher weight of the SF-BREEZE compared to the comparable diesel ferry, the SF-BREEZE has more on-board power in order to make 35 knots. This higher power makes the ferry consume more hydrogen, and when combined with the fact that making LH2 is much more energy intensive than making diesel fuel. However, using renewable LH₂, WTW GHG emissions for the SF-BREEZE ferry are reduced 75.8% compared to the diesel-fueled Vallejo.

Compared to Vallejo Tier 4 emissions using diesel fuel, the SF-BREEZE using LH₂ derived from steam reforming of fossil natural gas reduces WTW emissions of NO_x by 51.3%, HC by 68.8%, but PM emissions increase a factor of 2.5 times. Using LH₂ made from 100% renewable electricity, there would be a WTW 99.1% reduction in NO_x, a 99.2% reduction in HC, and a 98.6% reduction in PM compared to the Vallejo running on diesel fuel with Tier 4 emission constraints.

Regulations and economics. ABS issued a conditional Approval in Principal to verify that the conceptual design would be compliant with applicable regulations and rules and to identify any potential gaps in compliance. Combining their assessment with feedback from the USCoast Guard, Sandia found no regulatory show-stoppers and concluded that the vessel will be acceptable from a regulatory perspective once a more detailed “ready-to-build” design is generated.

The hydrogen ferry would cost about twice as much as a comparable diesel ferry with today’s prices. Much of that cost is in the fuel cell system.

Right now, we can’t achieve economic parity with a comparable diesel ferry. But this is a question we need to explore further. Is economic parity necessary from the outset? Lessons from the automotive market tell us maybe not.

—Joe Pratt, Sandia co-author

Vehicle manufacturers have successfully brought fuel cell electric vehicles to market even though those cars are more expensive than comparable internal combustion engine vehicles. Many experts expect mass adoption of fuel cell electric vehicles to bring down prices of hydrogen fuel cells.

Optimization. The next step is to optimize the vessel design. Working with Red and White Fleet and other stakeholders, Klebanoff and Pratt are now undertaking an optimization study. They will examine the tradeoffs between speed and costs and emissions among other factors.

Red and White Fleet President Escher sees SF-BREEZE as the start of a revolution in marine transportation.

When this boat is launched, it will be a seed. When you add a seed to water, it grows. This seed could grow into a 40-meter tugboat, a 70-meter supply boat or a 300-meter oceangoing ship trading between the West Coast and Hawaii. And all at zero pollution.

—Tom Escher

Resources

• Joseph W. Pratt and Leonard E. Klebanoff (2016) “Feasibility of the SF-BREEZE: a Zero-Emission, Hydrogen Fuel Cell, High-Speed Passenger Ferry” SAND2016-9719