BW LPG plans to convert the first two vessels, BW Leo and BW Gemini, this year.
The other vessels are targeted for conversion at their next drydocking period.
The vessels will be fitted with two additional LPG cargo/fuel deck tanks in the cargo area, so as not to compromise the cargo capacity on board and a high-pressure liquid fuel system for the modified MAN Energy Solutions two stroke engines.
Using LPG as a ship fuel results in lower emissions to air, eliminating most sulphur emissions, and reducing particulate matter and black carbon emissions.
When used with a two-stroke engine, LPG can also significantly cut NOx emissions and reduce greenhouse gas emissions.
BW LPG said retrofitting can extend the lifespan of the vessel, significantly reducing the overall carbon footprint compared to a newbuilding.
Chief executive, Anders Onarheim said the move is an opportunity to invest resources and expertise to pioneer technology that can be used to push the industry towards decarbonisation without having to order newbuildings.
In August 2018, the company announced the project to convert some LPG carriers to an LPG-fuelled propulsion system.
The flag state acceptance of the design by the Isle of Man means the project has demonstrated an equivalent level of safety to methane as a ship fuel under the IGC Code 2016.
Isle of Man Ship Registry director Cameron Mitchell said “In the age of constant change, technological advances and forward thinking, the Isle of Man Ship Registry and the Ship Registry’s global client base of shipowners and operators are very keen to put their collective experience to good use, working collaboratively and embracing innovation within the maritime industry.”
DNV GL chief executive Knut Ørbeck-Nilssen said the knowledge the company has gained from working on the project has resulted in DNV GL being able to release a new dedicated LPG notation.
DNV GL has developed new class rules and class notations for the LPG market in anticipation of an increased uptake of the fuel this decade.