Diesel-electric and integrated electric propulsion feed propulsion motors, thrusters and hotel loads from one electrical bus, while DC grids let gensets run at variable speed and connect batteries directly. ABB, Siemens Energy and GE Vernova lead the segment, which now underpins hybrid ferries, offshore vessels, naval combatants and the first cruise-ship DC retrofit.
What it is and how it works
In a diesel-electric plant, several generator sets feed a common electrical bus, and the propulsion motors, thrusters and hotel loads all draw from that bus. Engine speed is decoupled from propeller speed, so the ship runs only as many gensets as the load requires. Integrated electric propulsion (IEP) applies the principle to the whole ship, and integrated full electric propulsion (IFEP) is the naval version in which gas turbines and diesel gensets share one grid. GE Vernova says it powers most of the Royal Navy's large fleet on this basis, including the Queen Elizabeth class, Type 45 and Type 26.
A DC grid takes the idea further. Variable-speed gensets rectify onto a DC bus, so each engine runs near its optimal load instead of being locked to 50 or 60 Hz, and batteries or fuel cells connect to the bus without AC synchronisation. ABB markets this as Onboard DC Grid, with a Compact Onboard DC Grid variant for vessels up to about 1 MW and a separate Dynamic AC concept for larger ships (ABB).
Why it matters now
DC grids are the platform beneath the battery-hybrid fleet of ferries, offshore support vessels and tugs, and they are now entering cruise retrofits. IFEP is also the architecture that pod propulsion assumes and that nuclear and fuel-cell developers take for granted in their all-electric ship concepts. Siemens Energy reports that its BlueDrive PlusC low-voltage DC platform has been installed on more than 60 vessels, and it supplied the propulsion for the battery ferry Ampere and for Fjord1's two all-electric Anda-Lote ferries. Multi-megawatt DC platforms are implied by the 16-55 MW shore-charging levels now planned for the largest electric ferries, although no sourced data on medium-voltage DC adoption was found.
Key players and products
ABB offers Onboard DC Grid, Compact Onboard DC Grid and Dynamic AC, and supplies the DC grid, energy storage and automation for Washington State Ferries' hybrid programme (EEPower). Siemens Energy sells BlueDrive PlusC and the compact BlueDrive Eco for ferries, yachts, offshore vessels and smaller ships. The Switch, part of Yaskawa, supplies DC-Hub distribution alongside its permanent-magnet machines. Kongsberg Maritime integrates hybrid and electric plants. In March 2024 GE Vernova's power-conversion business won the electric grid and IFEP package for Singapore's six-ship Multi-Role Combat Vessel programme, covering generators, medium-voltage switchboards, transformers, propulsion drives, motors and power management (Naval News). From 1 January 2025 that unit was merged into a Power Conversion & Storage segment, with no divestiture reported (GE Vernova 10-Q).
Figures that matter
The most cited numbers come from ABB's 2014 verification on the platform supply vessel Dina Star, which recorded up to 27% lower specific fuel consumption, 14% fuel saving in dynamic positioning and 30% less engine-room noise (ABB). ABB also states that variable-speed DC operation gives partial-load savings of up to about 20% for medium-speed and about 40% for high-speed engines, and claims 4-6% annual savings for Dynamic AC (ABB). All of these are vendor trial results or vendor claims. No independent fleet dataset and no installed-base count for Onboard DC Grid were found.
| Metric | Value | Source type | Source |
|---|---|---|---|
| Specific fuel consumption reduction, Dina Star trial | up to 27% | vendor | ABB |
| Fuel saving in DP, Dina Star trial | 14% | vendor | ABB |
| Engine-room noise reduction, Dina Star trial | 30% | vendor | ABB |
| Claimed partial-load saving, variable-speed DC | ~20% medium-speed, ~40% high-speed | vendor | ABB |
| Claimed annual saving, Dynamic AC | 4-6% | vendor | ABB |
| BlueDrive PlusC installed base | more than 60 vessels | trade-press | — |
| Singapore MRCV IFEP programme | six ships | trade-press | Naval News |
Developments 2023-2026
- March 2024: GE Vernova wins the IFEP and ship electric grid package for Singapore's six Multi-Role Combat Vessels.
- January 2025: GE Vernova folds its power-conversion business into a Power Conversion & Storage segment without a divestiture.
- 2025: MS Amera (Phoenix Reisen) becomes the first cruise ship fitted with ABB Onboard DC Grid in a turnkey AC-to-DC replacement (The Motorship).
- 2025: Washington State Ferries' hybrid conversions and newbuilds run on ABB Onboard DC Grid, energy storage and automation.
- December 2025: ABB publishes a paper on using Onboard DC Grid for enhanced DP operations on low-voltage vessels (Dynamic Positioning Conference).
- Siemens Energy's BlueDrive PlusC passes 60 vessel installations, the only platform count retrieved for any DC grid product.
Outlook
Growth in DC grids tracks the battery fleet rather than deep-sea tonnage: the Maritime Battery Forum register passed 2,000 vessels in October 2026, and nearly every hybrid or electric ship on it needs a DC or variable-frequency bus. The open questions are higher-voltage DC for multi-megawatt ferries, whether cruise retrofits like MS Amera turn into a series, and how much of the vendor-reported saving survives independent measurement across varied load profiles. Buyers should re-check the ABB trial figures against primary data before writing them into contracts.
