The agency says it's also aiming to have the hulls of the Spirit of Vancouver Island and the Spirit of British Columbia modified and has filed an application with the BC Ferries commissioner.
BC Ferries says the modifications would save about $9.2 million annually over the remaining 27-year life cycle of the two vessels.
Ferries president Mike Corrigan says LNG is 50 per cent cheaper than marine diesel and the conversions, planned separately between 2016 and 2018, would also bring environmental benefits.
The former Crown corporation says it spent $126 million on fuel last fiscal year and that the two Spirit-class vessels, the largest diesel consumers in its fleet, guzzled about 15 per cent of the total bill.
The two vessels operate on the Tsawwassen-to-Swartz Bay route, which carried 28 per cent of total passengers in the fiscal 2014 year.
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