DSME and DNV GL discuss more efficient LNG carrier for the post-Panamax age
April 26, 2017
DSME and DNV GL discuss the results of a new collaborative project to design a larger, more efficient LNG carrier for the post-Panamax age
LNG carriers are changing. As Arctic trade routes and frontier projects like Yamal LNG open up to the north, and with the widening of the Panama Canal ongoing in Central America, new designs are creating bigger, more powerful and more efficient vessels.
In its annual report, the International Gas Union (IGU) noted that LNG was playing an essential role in the marine shipping sector, with 31 newbuilds added to the shipping fleet in 2016, an increase of around 7% to 439 vessels in total. Only two vessels were scrapped in the year.
However, all of this comes during a glut of gas supply. Average charter rates fell below US$20,000 per day during the year, and a new tranche of newbuilds in 2017 may exert even further pressure in the short term, before supply and demand begin to level out post-2020. The result is that new designs being drawn up currently are concerned with maximising efficiency and cargo capacity, and that means better propulsion, hull profiling and increased data capture.
At this year’s Gastech conference in Tokyo, Daewoo Shipbuilding & Marine Engineering (DSME) and classification society DNV GL presented the results of a joint development project (JDP) for the design of one such innovative LNG carrier. According to DNV, the project focused on producing a design “which an owner can take straight to the yard” in addition to being prepared for incoming regulations and market trends.
“When we look at today’s LNG market we predict that in the years to come we will see the rise of post-Panamax LNG carrier designs which are dimensioned to fit the new Panama Canal. Capacities of over 175,000 cubic metres are feasible given the new restrictions,” commented DNV GL’s maritime business director for gas carriers, Johan Petter Tutturen, at the time.
The Panama Canal expansion will see the route accommodate vessels of up to 180,000 cubic metres, a figure borne out in the IGU’s record, which notes that the average orderbook vessel capacity at the end of 2016 was 172,000 cubic metres.
Taking the initiative “It was DSME that took the initiative to this JDP,” Tutturen told InnovOil. “In the past DNV GL had done the LNGreen I project with HHI (as well as GTT and GasLog), followed by LNGreen II which is ongoing. Furthermore, we had the LPGreen JDP, also with HHI and Consolidated Marine Management and Wärtsilä. The common goal for these projects was to carry as much cargo as possible at the lowest cost, meaning the focus was put on optimising the hull lines and propulsion.” For this latest project, DSME wanted to widen the scope to include other innovations, such as its MCTIB fuel tanks and a partial re-liquefaction system (PRS).
The JDP began with a comprehensive market study to help determine what design features would be most important. “We looked at trends, trading routes, which geographical regions LNG was shipped (out from and within), the LNG trading mechanisms – such as an increase in spot trade, (accepting the fact that more cargoes may be re-sold during voyage, hence the trading pattern may be more difficult to predict),” he said. Described as the “DSME Post-Panamax 200K LNG Carrier,” its new design is 300m long by 48.9m wide, with a depth of 27.5m and a designed draft of 11.9m. Four cargo tanks allow for 200,000 cubic metres using membrane-type cargo containment system (CCS) or 170,000 cubic metres using DSME’s high-manganese steel Type B tank, known as MCTIB. It is also suitable for conversion into a floating storage and regasification unit (FSRU). “The maximum allowable width of vessels passing through the new Panama Canal is 49 metres,” Tutturen said. “It was natural to take advantage of this width increase, while the other main particulars were kept as-is for a vessel being built today.”
DNV draws attention to the shift towards lower, more energy-efficient transit speeds. As result, the JDP vessel design features an optimised hull and propulsion system, aimed at three different operating profiles on a standard Trans-Pacific route: 19.5, 16 and 12 knots. In calm water, these are 6%, 2% and 5% more efficient over the reference design at each operating profile respectively. “The engines become more energy-efficient: hence you will have surplus boil-off at low speed – that’s why the PRS was introduced,” Tutturen continued. The project participants noted that over 700 different hull designs were explored and run through DNV GL’s hydrodynamic analysis software Wasim, as well as statistics and Reynolds-averaged Navier-Stokes (RANS) simulations for determining wave resistance. “We have run a full hydrodynamic analysis for a 192K vessel, but DSME wants to increase the size to 200K, which is now being worked on,” he said.
The design also incorporates direct-coupled, two-stroke dual-fuel (DF) main engines and DF auxiliary engines, which use LNG as their primary fuel. A combined gas turbine, electric and steam (COGES) propulsion system is used for the optimised machinery.
Extra in the tank The MCTIB was chosen as the optimal choice to hold the portion of the boil-off gas used as LNG fuel, and has been tested in closed, mock-up conditions using liquid nitrogen (LN2). DNV notes that the material’s sound tensile properties enable high performance and high gas capacity at low cost.
“It is a manganese-based alloy steel and shares the same crystal structure with austenitic stainless steel,” Tutturen added. “As you can see [in the comparison table], the high manganese steel has high potential competitiveness than others.” This also allows for flexible tank shapes while remaining slosh-free, thereby not imposing any limitations on filling.
The design also incorporates DSME’s SloT® (Ship Internet of Things) technology and wireless computer network and integration system Smartship 4.0. Tuttern elaborated: “In short it means [taking] advantage of all data collected while in operation to facilitate a more robust maintenance scheme and cyber-security, as well as provide a system where all components manage to “talk” with each other.”
Despite the influx of newbuilds on their way in the coming years, the JDP partners seem confident that the added efficiency and capabilities of the post-Panamax design will allow it to hold its own in a tough market. Only time will tell, but their focus on the key driver – carrying as much cargo as possible at the lowest cost – should help keep DSME’s order book healthy.