Marine steam turbine propulsion was the standard LNG carrier prime mover because boilers burn boil-off gas simply, but at about 30% thermal efficiency it trails DFDE plants above 42% and two-stroke gas engines by more. Record scrapping in 2025 and widening lay-ups in 2026 leave nuclear as the only growth route for marine steam.
What it is and how it works
Marine steam turbine propulsion burns fuel in boilers to raise high-pressure steam, expands it through a turbine and drives the propeller through a reduction gearbox. For decades it was the standard prime mover of LNG carriers because a boiler burns cargo boil-off gas, heavy fuel oil or any mix of both simply and reliably. The penalty is efficiency: a steam plant reaches only about 30% thermal efficiency against over 42% for a four-stroke diesel-electric (DFDE) plant, roughly a one-third fuel saving for the diesel, according to the Journal of Maritime Research. Two-stroke gas engines widen the gap further; the ME-GI is reported as up to 30% more fuel-efficient than steam turbine propulsion.
Steam ships made up 47% of the LNG carrier fleet in 2018 (UCL) and about 38% in a 2020 count that put DFDE at 19%, TFDE at 14%, ME-GI at 11% and X-DF at 6% (Journal of Applied Engineering Science). No reliable 2025 or 2026 fleet split was found, and market-research estimates conflict.
Why it matters now
EEXI and CII compound the charter-market disadvantage of steamships, so demolition now tracks LNG freight rates and dry-dock due dates, and the replacement tonnage is almost entirely two-stroke. Analysts quoted by Hellenic Shipping News attribute the scrapping wave to the performance gap between older steam ships and modern two-stroke or TFDE vessels, and note that DFDE and TFDE ships are now also under commercial pressure. The only growth route for marine steam is nuclear, where a reactor replaces the boiler.
Key players and products
Flex LNG switched its newbuilds from DFDE to ME-GI in 2015, estimating that the fuel reduction against a typical steam carrier was more than double that of DFDE (Offshore Energy). Everllence (formerly MAN Energy Solutions) and WinGD supply the ME-GI and X-DF two-strokes that replace steam plants. Drewry, Argus and Hellenic Shipping News track the demolition wave; Capital Gas and Hyundai LNG Shipping were among 2025 sellers (TradeWinds).
Figures that matter
Flex LNG's third-quarter 2025 call, reported by Argus Media, counted 14 LNG carriers scrapped in the first nine months of 2025 against 8 in all of 2024 and an average of 5 a year over 2020-2024. About 120 steam turbine vessels are open or coming off charter in the next few years (Argus Media). By February 2026 over 60 LNG carriers were idled, of which steam ships made up about 70%. Drewry expects more than 100 steam carriers to be demolished by 2030, generating demand for 75-85 replacement vessels.
| Metric | Value | Source type | Source |
|---|---|---|---|
| Steam plant thermal efficiency vs DFDE | about 30% vs over 42% | verified | Journal of Maritime Research |
| ME-GI advantage over steam | up to 30% more fuel-efficient | trade-press | — |
| Steam share of LNGC fleet | 47% (2018); about 38% (2020) | verified | UCL; JAES |
| LNGCs scrapped, Jan-Sep 2025 | 14 (8 in all of 2024) | trade-press | Argus Media |
| Steam ships open or off charter | about 120 | trade-press | Argus Media |
| Steam share of 60+ idled LNGCs, Feb 2026 | about 70% | trade-press | Hellenic Shipping News |
| Steam LNGCs demolished by 2030 (forecast) | more than 100; 75-85 replacements | aggregator | Drewry |
| Core Power and MARAD nuclear fleet plan | 50 ships, first delivery about 2033 | trade-press | World Nuclear News |
Developments 2023-2026
- 2025: Hyundai LNG Shipping makes the first LNG carrier scrap sale of the year; eight carriers are gone by end-July, already a record, with Capital Gas linked to a demolition.
- 2025: Core Power and the US Maritime Administration sign a memorandum of cooperation envisaging a 50-ship fleet of LNG tankers and container ships with first delivery around 2033 using a BWX Technologies reactor (World Nuclear News); a consortium with HD Korea Shipbuilding and Southern Co. targets a fission-powered ship by 2035, although insurers reportedly will not yet cover such vessels (EBSCO).
- February 2026: more than 60 LNG carriers idled, about 70% of them steamships, and DFDE and TFDE tonnage comes under pressure next.
Outlook
Steam LNG carriers are now effectively a scrapping and lay-up pool rather than an operating technology class, and every replacement order is a two-stroke ME-GI or X-DF ship. Nuclear would bring the steam turbine back as a prime mover, but every announced first-ship date, 2033 to 2035, lies beyond the 2026-2030 regulatory horizon and the insurance and port-access barriers remain unresolved. Current naval nuclear steam plants were not covered by this research.
