Van Oortmerssen Power Prediction Calculator

A power prediction method for small ships based on resistance calculation

Based on work by G. Van Oortmerssen
Vessel Parameters
Resistance Calculation
Results & Power

Vessel Particulars

Water Properties

Sum of roughness allowances (from Table V)

Calculation Options

to kn
Table I - Correlation Allowances (ΔCF)
Item Allowance Description
1 0.00035 Roughness all-welded hull
2 0.00004 Steering resistance
3 0.00004 Bilge keel resistance
4 0.00008 Air resistance
Total 0.00051 Sum of correlation allowances
The total correlation allowance (ΔCF) above sums to 0.00051. The default value in the input field is set to 0.0004. Adjust as needed based on your vessel's specific characteristics.

Method Applicability Check

Range of Validity Check

The Van Oortmerssen method is applicable within the following ranges:

8 < LWL < 80 m
OK: 30.5 m
5 < ∇ < 3150 m³
OK: 376 m³
3 < LWL/B < 6.2
OK: 3.63
1.9 < B/T < 4
OK: 2.85
0.5 < Cp < 0.725
OK: 0.579
10 < iE < 46 deg
OK: 23 deg

Method is applicable for this vessel

All parameters are within the valid range

Derived Parameters

Parameter Symbol Value Unit
Displacement length, LD LD 29.00 m
Displacement, D Δ 385.40 t
LD / B LD/B 3.45 -
B / T B/T 2.85 -
Midship section coefficient, CM CM 0.823 -
Waterplane coefficient, CWL CWL 1.05 -

Regression Coefficients (Table II)

Index c1 c2 c3 c4
0 79.32134 6714.88397 -908.44371 3012.14549
1 -0.09287 19.83 2.52704 2.71437
2 -0.00209 2.66997 -0.35794 0.25521
3 -246.45896 -19662.024 755.1866 -9198.8084
4 187.13664 14099.904 -48.93952 6886.60416
5 -1.42893 137.33613 9.86873 -159.92694
6 0.11898 -13.36938 -0.77652 16.23621
7 0.15727 -4.49852 3.7902 -0.82014
8 -0.00064 0.021 -0.01879 0.00225
9 -2.52862 216.44923 -9.24399 236.3797
10 0.50619 -35.07602 1.28571 -44.1782
11 1.62851 -128.72535 250.6491 207.2558
These coefficients are used in the residuary resistance calculation as per Van Oortmerssen's method.

Resistance Calculation Details

The following calculations are performed for each speed in the specified range.

For Design Speed: 13 kn

Parameter Formula Value Unit
Froude number, Fn V/√(g·LD) 0.405 -
Reynolds number, Rn V·LD/ν 6.83×108 -
Frictional coefficient, CF 0.075/(log10Rn - 2)² 0.00172 -
Total friction coefficient, CF+ΔCF CF + ΔCF 0.00212 -

Residuary Resistance Calculation

m = 0.14347 × CP-2.1976 = 0.518
f1 = exp(-m/(9·Fn²)) = 0.192
f2 = exp(-m/Fn²) = 0.014
f3 = exp(-m/Fn²)·sin(1/Fn²) = 0.010
f4 = exp(-m/Fn²)·cos(1/Fn²) = 0.010
RR/Δ = c1·f1 + c2·f2 + c3·f3 + c4·f4 = 0.00742

Resistance Components

Component Formula Value Unit
Frictional resistance, RF 0.5·ρ·S·V²·(CF+ΔCF) 29560 kgf
Residuary resistance, RR (RR/Δ)·Δ·1000 2858 kgf
Total resistance, RT RF + RR 32418 kgf
Total resistance RT × 0.00980665 317.9 kN

Effective Power

PE = RT × V = 32418 kgf × 6.69 m/s = 2129 kW
Resistance Summary
Frictional resistance: 29560 kgf
Residuary resistance: 2858 kgf
Total resistance: 32418 kgf
Effective power: 2129 kW
Resistance Ratios
RF/RT: 91.2%
RR/RT: 8.8%
RR/Δ: 0.0074
RT/Δ: 0.0841

Power Prediction Results

The table below shows the resistance and power calculations for the specified speed range.
Speed (kn) Speed (m/s) Fn Rn (×108) CF+ΔCF RF (kgf) RR/Δ RR (kgf) RT (kgf) RT (kN) PE (kW)

Resistance Components vs. Speed

Effective Power vs. Speed

Vessel Summary
Displacement: 385.4 t
Length between perpendiculars: 27.5 m
Beam: 8.406 m
Draft: 2.949 m
Design Speed Performance
Design speed: 13 kn
Froude number: 0.405
Total resistance: 317.9 kN
Effective power: 2129 kW
Coefficients
Prismatic coefficient: 0.579
Midship coefficient: 0.823
Waterplane coefficient: 1.05
Block coefficient: 0.477