Flettner Rotor Wind Assist

Rotating vertical cylinders generate thrust via the Magnus effect in crosswinds. Annual fuel saving depends on wind climate, ship route and rotor height - typical installed systems report 5–15 % main-engine fuel savings on wind-rich trades.

DesignWind assist

Rotor array

Number of rotors–Rotor heightmRotor diametermRotor drive power per unit (spin-up)kW

Wind climate

Average apparent-wind speedm/sFraction of voyage hours with useful cross wind%North Atlantic 50–70 %, Indian Ocean monsoon seasons 60–80 %, equatorial 20–30 %.

Displacement

ME SFOCg/kWhSea hours / yearhFuel

Effective thrust × speed power: 0kW

Net fuel saved / year: 0.0t

CO₂ avoided / year: 0.0t

Changing the inputs requires JavaScript. The calculator above shows its default inputs and result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

P_\text{gen} = C_L \cdot \tfrac{1}{2} \rho_\text{air} V^2 A \cdot V_\text{ship}

Symbol	Meaning	Unit
$P_\text{gen}$	Gross thrust power from all rotors	kW
$P_\text{net}$	Net main-engine saving after rotor-drive cost	kW
$C_L$	Lift coefficient for rotating cylinder at spin ratio ~3
$\rho_\text{air}$	Air density	kg / m³
$V$	Apparent wind speed	m / s
$A$	Total rotor projected area ( $N \cdot h \cdot d$ )	m²
$V_\text{ship}$	Ship speed	m / s
$f_\text{useful}$	Share of voyage hours with useful cross-wind	fraction
$N$	Number of rotors
$P_\text{drive}$	Drive-motor power per rotor	kW

Source: Norsepower - *Rotor Sail in-service results*; Anemoi Marine Technologies - *Rotor Sails*; IMO Resolution MEPC.1/Circ.815 - innovative energy-efficient technologies

In short

Estimate fuel and CO₂ saving from Flettner rotors (Magnus-effect wind assist) on a merchant ship.

Learn the theory Decarbonization Technologies for Ships