Technology
How Vessels Multiply Their Own Wind Resource
A vessel at sea does not simply experience the ambient wind. It creates a localised wind field -- shaped by its hull, superstructure, and forward motion -- that can multiply available wind energy by a factor of three or more at the points where turbines are mounted.
The physics
As wind passes over a vessel's superstructure, it is compressed and accelerated in the same way air speeds up through the narrow section of a venturi tube. The taller and broader the superstructure, the more pronounced the effect.
At 3 m/s ambient wind speed -- a light breeze -- effective airflow over the deck and around the superstructure reaches 9 m/s or more depending on vessel geometry and turbine placement. This is not a theoretical maximum; it is the starting point for conservative installation planning.
A vessel cruising at 10 knots adds a further 4 to 7 m/s apparent wind factor on top of the ambient wind. The result is that a vessel underway in modest sea conditions is a high-performance generation environment -- one that exists regardless of the weather forecast.
Vessel motion
Even in genuinely calm conditions, a vessel's own forward progress generates apparent wind across the deck. A ship cruising at 10 knots (approximately 5 m/s) in completely still air experiences 5 m/s of apparent wind at the bow, reducing toward the stern depending on superstructure geometry.
This means H Nordic turbines are generating from 2 m/s onward not just in windy conditions -- they are generating whenever the vessel is underway. On a commercial route with 6,500 operating hours per year, that represents a very large proportion of total sailing time.
Typical ambient wind speed used as the baseline for conservative fuel savings calculations.
Effective airflow over deck at 3 m/s ambient -- the venturi effect applied to a typical cargo vessel geometry.
Additional apparent wind from vessel forward motion at 10 knots -- additive to ambient and venturi effects.
H Nordic cut-in speed -- DC-direct battery storage means generation begins in the lightest conditions.
Placement
Turbine position on the vessel is as important as turbine count. The venturi effect is not uniform across the deck -- it is strongest at specific points determined by superstructure height, hull beam, and the interaction between vessel geometry and prevailing wind angles on the route.
H Nordic conducts a deck layout assessment for each vessel as part of the delivery scope. Positions are selected to maximise the venturi benefit at each mounting point, account for wake and shadow interactions between units, and avoid interference with cargo operations, navigation equipment, and safety clearances.
The reference configuration -- four 100 kW units -- is used for initial vessel assessments. Eight-unit and mixed 50/100 kW configurations are specified where deck layout allows greater coverage.
Aerodynamics
The fuel savings from H Nordic turbines exceed what direct electricity generation alone would explain. The reason is aerodynamic drag reduction.
Vessels moving through air experience vortex shedding -- turbulent rotating airflows that form at the edges and corners of the superstructure and create resistance. These vortices contribute meaningfully to total aerodynamic drag, particularly on vessels with large flat superstructure faces such as car carriers and RoRo vessels.
Turbines mounted at the leading edges of the superstructure disrupt the formation of these vortices. The airflow that would otherwise roll into resistance-generating turbulence is instead captured by the rotor. The result is a measurable reduction in propulsion energy requirements -- a second-order fuel saving that is separate from, and additional to, the electricity the turbines generate.
Evidence
In 2011, Stena Line installed two 4 kW turbines on the Stena Jutlandica and recorded fuel savings of 80 to 90 tonnes per year. The direct electrical output of two 4 kW turbines -- even running continuously -- cannot account for savings of that magnitude.
The most credible explanation is aerodynamic drag reduction through vortex disruption. The turbines changed the airflow around the vessel in a way that reduced propulsion resistance. The fuel saving was a system-level effect, not a generation-only calculation.
H Nordic turbines in the 50 to 100 kW range are substantially larger, produce more electricity directly, and exert a proportionally greater effect on the vessel's aerodynamic envelope. The combined saving -- generation plus drag reduction -- is the basis for the fuel savings figures published in the fuel savings model.
Compatibility
| Vessel type | H Nordic VAWT | Notes |
|---|---|---|
| Car carriers (RoRo) | Highly suited | Large flat superstructure maximises venturi effect; clear deck areas for multi-unit layout. |
| Bulk carriers | Highly suited | Extensive open deck; superstructure geometry favourable; high operating hours. |
| Container vessels | Suited | Mounting positions available above and around superstructure; subject to deck layout review. |
| Ferries | Suited | High operating hours; fixed routes allow precise wind modelling; Stena Jutlandica precedent directly applicable. |
| Offshore support vessels | Suited | Subject to deck equipment review; operational profile typically favourable. |
| Tankers | Suited | Large deck areas; subject to ATEX zone assessment for turbine placement near cargo handling equipment. |
The venturi effect is the mechanism. The savings table shows what it means in fuel and dollars.
Fuel savings model Request a vessel assessment