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.

DesignPropeller

Hull particulars

Block coefficient Cb–Length between perpendicularsmBeammConfiguration

Bare-hull input

Bare-hull resistance RTkNShip speedkn

Wake fraction w: 0.360–

Thrust deduction t: 0.226–

Hull efficiency η_H = (1−t)/(1−w): 1.209–

Advance velocity V_A: 4.61m/s

Required thrust T: 1,033.6kN

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

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.

Learn the theory Decarbonization Technologies for Ships