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Calcimator

Marine Outfall Design Calculator

Estimate the structural and hydrodynamic impact of marine growth (biofouling) on offshore members — effective diameter, added weight, and drag/inertia force increases.

Inputs

Results

Effective OD with growth (m)

1.2

Total growth mass (kg)

13,736.6

Drag force increase (%)

93.8

Diameter increase (%)20
Submerged weight of growth (N/m)1,017.03
Inertia force increase (%)62
Relative roughness (e/D)0.08
How to Use This Calculator
  1. Enter bare member outer diameter (m) and radial marine growth thickness (mm).
  2. Enter growth density (kg/m3) — hard fouling ~1325 kg/m3 — and member length (m).
  3. Enter drag coefficient for the clean (Cd clean) and fouled (Cd fouled) member.
  4. Read fouled member effective diameter and additional added mass from marine growth.
  5. Use increased drag force (kN/m) to update structural load calculations for the grouted member.

How the result changes with Bare member OD (m)

Bare member OD (m)Effective OD with growth (m)Total growth mass (kg)Drag force increase (%)
2.042.2426,72477.4
7.037.2389,038.266.1
1313.2163,590.664
1818.2226,029.763.3

What each input means

Bare member OD (m)
Outer diameter of the structural member without marine growth.
Growth thickness (mm)
Radial thickness of marine growth. DNV-RP-C205: 50-100mm typical splash zone, 20-50mm subsea.
Growth density (kg/m³)
Mass density of marine growth. Hard fouling ~1325, soft ~1100 kg/m³.
Member length (m)
Length of the member over which growth is present.
Cd clean
Drag coefficient for the clean (smooth) member.
Cd fouled
Drag coefficient for the fouled (rough) member per DNV-RP-C205.
Max wave velocity (m/s)
Maximum horizontal water particle velocity for drag comparison.
Cm clean
Inertia coefficient for clean member.
Cm fouled
Inertia coefficient for fouled member.

What each result means

Effective OD with growth (m)
Member diameter including marine growth on both sides.
Diameter increase (%)
Percentage increase in effective diameter.
Total growth mass (kg)
Mass of marine growth over the full member length.
Submerged weight of growth (N/m)
Submerged weight of growth per meter of member.
Drag force increase (%)
Increase in wave drag due to larger diameter and higher Cd.
Inertia force increase (%)
Increase in wave inertia force due to larger cross-section and higher Cm.
Relative roughness (e/D)
Growth thickness divided by effective diameter — used for Cd selection.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Bare member OD (m) = 1, Growth thickness (mm) = 100, Growth density (kg/m³) = 1325, Member length (m) = 30 = 9 input(s) provided
  2. Calculate Effective OD with growth
    Effective OD with growth = memberDiameter + 2 * tGrowth
    1.2 = 1.2
  3. Calculate Total growth mass
    Total growth mass = growthMassPerM * memberLength
    13736.6 = 13736.6
  4. Calculate Drag force increase
    93.8 = 93.8
  5. Calculate Diameter increase
    Diameter increase = round(((effectiveDiameter - memberDiameter) / memberDiameter) * 10000) / 100
    20 = 20
  6. Calculate Submerged weight of growth
    Submerged weight of growth = growthArea * (growthDensity - rho) * 9.81
    1017.03 = 1017.03

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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