A shaft generator lets the main engine supply hotel load in PTO mode and, as a permanent-magnet machine, motor the shaft from gensets or batteries in PTI mode. Wartsila puts the EEXI gain at 3-5%, and ABB booked 30 LNG carriers in one order, while superconducting motors remain in naval research.
What it is and how it works
A shaft generator is mounted on the propeller shaft, either in-line or through a gear, and lets the main engine, the most efficient machine aboard, supply the ship's hotel load in power take-off (PTO) mode. In power take-in (PTI) mode the same permanent-magnet (PM) machine motors the shaft from gensets or batteries, enabling take-me-home operation and electric port manoeuvring. A 15-20,000 TEU container ship typically carries one propulsion line with a shaft generator of about 5 MW, and with a clutch the PTI function allows full-electric port manoeuvring and safe return to port (MarineLink). PM machines outperform induction machines on efficiency and size for marine duty (The Switch); high-temperature superconducting (HTS) motors promise far higher power density but remain experimental.
Why it matters now
Wartsila calls shaft generators the next-best technical option for EEXI compliance after energy-saving devices, improving ship energy efficiency by 3-5%. PM shaft generators have become the fastest-scaling electrical item in deep-sea newbuilding, ordered tens of ships at a time and tied directly to EEXI from 2023 and annual CII tightening. They also anchor hybridisation, pairing with batteries and energy management for take-me-home functions, as The Motorship reports.
Key players and products
ABB supplies in-line PM shaft generators with ACS880 drives. Wartsila has delivered more than 1,000 shaft generator systems (Wartsila) and completed the first in-line shaft generator retrofit with Berge Bulk. The Switch, the Yaskawa Environmental Energy business now being acquired by BEMAC and Mitsui, makes the PMM2000M, rated up to 12 MW per propulsion line, and the PMM850M, has booked its 500th shaft generator order and signed a five-year deal in 2022 to supply ABB with 16 PMM2000M machines for container ship shaft generators. WE Tech in Finland markets PM shaft generator packages with drives and energy management for CII and EEXI compliance.
Figures that matter
ABB claims up to 4% fuel-cost reduction plus about 1% from its drives, up to 20% space and weight saving and a 2-4 year payback (ABB). A market report's claim that an 18,000 TEU ship can move from CII band D to C on a shaft generator alone is vendor-style and unverified. DNV's chief executive cited a VLCC shaft generator retrofit with an 18-year payback at February 2026 fuel prices, a reminder that retrofit economics differ sharply from newbuild (MarineLink). On motors, AMSC and Northrop Grumman full-power tested a 36.5 MW HTS motor less than half the size and about 200 t lighter than the conventional DDG-1000 motors (Control Engineering), and a 2023 design study claims 5-10 times the power density for a 40 MW semi-superconducting machine, published in Scientific Reports, but HTS conductor price, mechanical weakness and manufacturing cost have kept the technology in naval research for two decades.
| Metric | Value | Source type | Source |
|---|---|---|---|
| EEXI efficiency gain from a shaft generator | 3-5% | vendor | Wartsila |
| ABB largest PM shaft generator order | 30 LNG carriers | trade-press | LNG Industry |
| Wartsila shaft generator systems delivered | more than 1,000 | vendor | Wartsila |
| ABB claimed fuel-cost reduction | up to 4% plus about 1% from drives | vendor | ABB |
| Typical boxship shaft generator, 15-20,000 TEU | about 5 MW | trade-press | MarineLink |
| The Switch PMM2000M | up to 12 MW per line | vendor | The Switch |
| VLCC retrofit payback, February 2026 fuel prices | 18 years | trade-press | DNV CEO via MarineLink |
| AMSC/Northrop HTS motor | 36.5 MW, about 200 t lighter | trade-press | Control Engineering |
Developments 2023-2026
- February 2025: ABB books its largest-ever PM shaft generator order, 30 LNG carriers (18 at Chinese and 12 at Korean yards) with deliveries in 2028-2030, after an earlier 15-ship Samsung Heavy Industries order delivering from mid-2026 (LNG Industry).
- Wartsila and Berge Bulk complete the first in-line shaft generator retrofit on a bulk carrier.
- The Switch launches the PMM850M for shaft generator and propulsion duty and passes its 500th shaft generator order.
- Berg Propulsion partners with Yaskawa to offer a propeller-shaft electric drive option.
- 2025: the start-up Hinetics claims an HTS-rotor motor at 98-99.5% efficiency, aimed at aviation first with ship propulsion as a possible later use, according to the University of Illinois.
- February 2026: DNV's chief executive warns that a VLCC shaft generator retrofit pays back in 18 years at current fuel prices.
Outlook
The clearest growth signal is PM shaft generators on LNG carriers and large container ships, where orders are counted in tens of ships per contract. No fleet-wide statistic on shaft generator uptake per year was found, so supplier cumulative totals are the only scale indicator. HTS motors will stay in naval development until conductor cost falls, leaving PM machines as the commercially growing motor technology, increasingly offered for propulsion lines up to about 12 MW.
