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

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This calculator requires JavaScript to compute its 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.

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