Wake Fraction & Thrust Deduction

Hull-propeller interaction factors. Wake fraction w reduces the water arriving at the propeller disk vs the ship speed; thrust deduction t increases the thrust the propeller has to deliver vs bare-hull resistance. Both come from Harvald regression or model-basin tests.

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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

w = 0.5 C_B - 0.05 \text{ (single screw)}, \quad w = 0.25 C_B - 0.05 \text{ (twin screw)}

Symbol	Meaning	Unit
$w$	Taylor wake fraction
$t$	Thrust deduction fraction
$\eta_H$	Hull efficiency
$C_B$	Block coefficient
$V$	Ship speed	m / s
$V_A$	Advance velocity at propeller disk	m / s
$R_T$	Bare-hull resistance	kN
$T$	Thrust required	kN

Source: Harvald - *Resistance and Propulsion of Ships* (1983); ITTC - *Propulsion Committee Standard Procedure*

In short

Hull-propeller interaction factors w, t, η_H using Harvald's closed-form regression.

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