Savitsky Planing-Hull Resistance & Propulsion Engine Selection Calculator

Resistance, EHP, BHP, maximum required power, and marine diesel engine matching using the Daniel Savitsky method. This version follows the Insel & Molland calculator layout and shows Insel & Molland-style charts and includes formula blocks at the bottom of the page.

Inputs

Hull & loading

Hull & loading

Calculation & propulsion

Automatic trim is solved for each speed. Engine matching uses the highest required power inside the selected speed range, then divides it across the selected number of engines.

Final calculated result

Equilibrium trim τe
—
deg
Total drag D
—
lb
EHP
—
hp
BHP
—
hp
Maximum required power
—
hp = BHP / margin
Equilibrium mean λe
—
ratio
Wetted keel length Lk
—
ft
Wetted chine length Lc
—
ft
Draft d
—
ft
Porpoising metric
—
screen
Porpoising status
—
trim screen
Vₘ/V at τe
—
ratio
Cp at τe
—
coefficient
Row 30 at τe
—
check
Status: —

Recommended propulsion engine(s)

Reference engine matching is approximate and should be verified against current manufacturer data sheets and class requirements before final selection.
Sizing speed in range
—
knots
Sizing total required power
—
HP
Required power per engine
—
HP

Charts

Speed vs EHP with displacement, transition, and planing regions
Green = displacement region, orange = transition region, blue = planing region. The red marker labels the EHP corresponding to the currently selected speed.
Maximum required power versus speed
Maximum required power = BHP / MCR service margin. Green = displacement region, orange = transition region, blue = planing region.
Savitsky trim and coefficient trends vs speed
Shows equilibrium trim, λe, Cp, and Vm/V across the selected speed range.

Speed range performance table

Detailed resistance, power, trim, geometry, and porpoising-screen results across the requested speed range.

Formula Summary

CLβ = Δ / (0.5 ρV²b²) Row30 = N(26) + Df(a − f) = 0 D = Δtanτ + Df/cosτ EHP = D × V / 550 BHP = EHP / η Maximum Required Power = BHP / MCR Margin Power per Engine = Maximum Required Power / Number of Engines Input Data ↓ CLβ ↓ Trim Solver ↓ Resistance (D) ↓ EHP ↓ BHP ↓ Maximum Required Power ↓ Engine Recommendation