Marine Outfall Design Calculator

Marine growth forms a layer around the entire circumference of the member, so the radial thickness you enter is added on both sides of the bare diameter — once for the growth on the near side, once for the far side. That's why effective diameter equals bare diameter plus 2 times growth thickness rather than growth thickness alone, and it's the same effective diameter that then drives both the drag and inertia force comparisons.

Marine growth is a biological material sitting fully submerged in seawater, so like any submerged object it displaces water and loses weight to buoyancy. The calculator subtracts seawater density (1025 kg/m³) from the growth density before multiplying by area and gravity, which is why growth density values only modestly above water density (soft fouling near 1100 kg/m³) produce a much smaller submerged weight per meter than the same volume would weigh in air.

Drag and inertia coefficients depend on surface roughness in ways that aren't a simple function of growth thickness alone — DNV's Recommended Practice DNV-RP-C205 (Environmental Conditions and Environmental Loads) and NORSOK N-003 publish Cd/Cm curves that account for roughness pattern, Reynolds number, and zone-specific fouling type, which this calculator doesn't model internally. You supply the coefficients from those references (or project-specific data) so the tool stays a force-increase comparison rather than a roughness-to-coefficient model that could mask an unjustified assumption.

No — it evaluates one growth thickness applied uniformly over the full member length at a single point in time. Real marine growth varies by depth zone (splash, tidal, subsea) and accumulates over the structure's service life, so for a full assessment you'd run this calculator separately for each zone's expected thickness, and periodically re-run it as design life progresses and fouling grows thicker.