The US-listed owner of 15 container vessels received a preliminary predetermination for two of its vessels, the 1987-built Horizon Spirit and Horizon Anchorage , to send the vessels to a non-US shipyard to install the necessary dual-fuel engines and LNG fuel system and tanks.

It has now received permission from the US Coast Guard for sending four older vessels to a foreign yard to have the same work done.

The other vessels are Horizon Trader , Horizon Navigator , Horizon Pacific and Horizon Pacific all built between 1972 and 1980 and powered with steam turbines.

Vessels operating in North American waters will be forced to use ultra-low sulphur fuel, or install a scrubber to continue using current fuels, when the 0.1% sulphur emission limit comes into force on January 1, 2015.

With natural gas prices much lower than other part of the world there is a clear economic benefit in switching to natural gas.

Some US owners bound by the Jones Act have recently ordered new tonnage with dual fuel capabilities allowing them to switch between normal liquid bunkers and natural gas.

However, the prices of the vessels that have to be built in US yards to meet the Jones Act requirements are significantly more expensive than equivalent vessels being built in Asia.

In November, Crowley placed an order with VT Halter Marine for a pair of container/ro-ro ships to be powered by LNG.

Earlier that month, Matson, which operates in the Pacific, recently ordered two 3,600 teu containerships with Aker Philadelphia shipyard that will burn either conventional bunker oil or LNG.

Totem Ocean Trailer Express also chose the dual-fuel design, with the option of using LNG, for two 3,100 teu containerships to operate in the US domestic trades that it ordered last year.

To retain permission to trade under the Jones Act in the US, Horizon Lines has had to submit the work to the US Coast Guard to determine the work is not considered a significant rebuild that should be undertaken at a more expensive US shipyard.

Horizon Lines has yet to announce where the conversion work will be undertaken.