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Safety and Navigational Risk Assessment for LNG-Fueled Passenger Ferry Vessels

Liquefied Natural Gas


    September 2014

  • WSF has completed safety, navigation and security risk assessments that evaluate using liquefied natural gas (LNG) as a fuel source for the Issaquah Class ferries. Read the executive summary and the report and appendices available on the left sidebar.


For nearly four years Washington State Ferries (WSF) has been conducting analysis, evaluation and detailed studies on an option to use LNG as a source of fuel for six Issaquah Class ferries. LNG is used world-wide and provides an opportunity to reduce fuel costs, and better the environment by decreasing emissions.

What is LNG?
In its gaseous state, LNG is the same fuel used to heat our homes and cook our meals. LNG is natural gas that has been cooled to -256 degrees Fahrenheit, at which point it is condensed into a colorless, odorless, non-toxic and non-corrosive liquid. In its liquefied form it occupies 1/640th of its original volume, which makes it easier to transport and store.

Saving money, cleaner environment, energy independence 
WSF burns more than 17 million gallons of fuel each year. Fuel is our fastest growing operating expense, representing 23 percent of the FY13-15 operating budget, compared to 11 percent in FY00-01. Switching from diesel to LNG could save approximately 40-50 percent at today’s pricing.

Operating WSF's six Issaquah Class vessels with LNG would significantly reduce emissions when compared with today's use of ultra-low sulfur diesel fuel. WSF's Air Emissions Model predicts emission reductions as follows:

  • 89 percent reduction in particulate matter 
  • 61 percent reduction in nitrous oxide 
  • 28 percent reduction in carbon dioxide
  • 59 percent reduction in sulfur dioxide 

Worldwide examples
Use of natural gas in transportation has been steadily increasing for the last decade. LNG is fast becoming a transportation fuel for transit buses, semi-trucks and ferries.

  • Since 2000 the Norwegian government has allowed the construction and operation of LNG passenger vessels. There are currently 20 car and passenger ferries operating in Norway that are fueled by LNG.
  • Both BC Ferries and Staten Island Ferries are studying options to retrofit their vessels from diesel to LNG fuel.
  • The Quebec Ferries Company has contracted for three new LNG ferries.
  • There are LNG passenger vessels currently under construction or in design for service in Argentina, Uruguay, Finland, and Sweden.

U.S. examples of LNG used in public transportation

Other LNG resources

WSF proposal
In Dec. 2011, WSF received conceptual approval from the U.S. Coast Guard to retrofit the propulsion system with new engines on the six Issaquah Class ferries  to use LNG as a source of fuel. In 2012, WSF selected Det Norske Veritas (DNV) to complete a safety and security plan, risk assessment, and operational manual for converting to LNG. DNV is a classification body that has been involved in developing international standards for the use of LNG in passenger vessels. On Nov. 18, 2013 WSF submitted a Waterways Suitability Assessment (WSA), which includes a safety and security assessment and risk management plan, to the U.S. Coast Guard for approval. The WSA concluded that the LNG proposal is inherently safe with risks as low as reasonably practicable.
Rendering of LNG tanks on Issaquah class ferry   rendering of LNG tanks on Issaquah class ferry
Renderings of LNG tanks on an Issaquah class ferry (click to enlarge)

Next steps
Pending U.S. Coast Guard approval and funding, WSF could begin the first conversion of an Issaquah Class ferry as early as 2016.  Below is the status of key efforts:

  • Safety and security assessments – The submission of the WSA marks the official starting point of the U.S. Coast Guard’s review process. WSF expects the Coast Guard to issue a finding regarding the LNG conversion proposal in 2014.
  • Legislative approval Once the U.S. Coast Guard rules on the WSA, WSF will then seek legislative approval and funding to move forward.    
  • Design/build LNG propulsion system – In Fall 2012, WSF issued a request for proposal (RFP) for the retrofit of its six Issaquah class ferries. The RFP required the contractor to purchase and install all the required equipment and get all the required approvals to allow the vessel to obtain a certificate of inspection from the U.S. Coast Guard for operation with LNG as a fuel. Two proposals were received. Following extensive evaluation, WSF determined the submittals were deficient. Once legislative approval has been received and a financing plan is in place WSF plans to seek industry input and re-issue a modified RFP.


Hadley Rodero
WSF Communications Manager