Marine Terminal & LNG Berth Engineering, OCIMF MEG4 Mooring Wind/Current & %MBL
OCIMF Vessel Mooring Wind, Current & Hawser %MBL Formula
Calculate Aerodynamic Wind Load (kN), Seawater Tidal Current Drag (kN), Combined Environmental Surge/Sway Force (kN), and Hawser Tension as % of Ship Design MBL.
A 1.6 m/s (~3.1 knot) tidal current pushes harder on a loaded tanker hull than a 22 m/s (43 knot) gale—because seawater is 837x denser than air!
Port berth engineers and LNG marine terminals size quick-release mooring hooks and HMPE / wire-rope spring lines using **OCIMF Mooring Equipment Guidelines (`MEG4`)**. Standard `30`-second Wind Gust `V_w` (`m/s`, Air Density `rho_a = 1.225` kg/m³) acting on Above-Water Projected Area `A_w` (`m²`) with Drag Coefficient `C_w` exerts **Wind Force `F_w = (0.5 * 1.225 * C_w * A_w * V_w^2) / 1,000`** (`kN`), whereas Seawater Current `V_c` (`m/s`, Seawater Density `rho_s = 1,025` kg/m³) acting on Submerged Cross-Section/Wetted Area `A_c` (`m²`, Coefficient `C_c` including shallow under-keel clearance amplification!) exerts **Current Drag `F_c = (0.5 * 1,025 * C_c * A_c * V_c^2) / 1,000`** (`kN`)! Distributing **Combined Load `F_{tot} = F_w + F_c`** across `N_{lines}` active mooring lines (applying a `1.15` unequal pretension load-sharing factor) checks **Line Stress `%MBL = (((1.15 * F_{tot}) / N_{lines}) / MBL) * 100%`** against the **OCIMF `55%` Ship Design MBL Working Limit** (`60%` winch brake render setting)!
Verify on an Aframax Tanker Berthed in a Tidal Estuary—Wind_Speed `V_w` = 22.0 m/s (B2), Wind_Area `A_w` = 1,450 m² (B3), Wind_Coeff `C_w` = 0.82 (B4 -> Wind Load `F_w = 352.5` kN in E2), Ebb_Current `V_c` = 1.60 m/s (B5), Submerged_Drag_Area `A_c` = 520 m² (B6), Shallow-Water_Current_Coeff `C_c` = 0.65 (B7 -> Current Load `F_c = 443.5` kN in E3!), Active_Spring_Lines `N` = 4 (B8), and Line_Design `MBL` = 1,150 kN (B9): Total Surge Load hits `795.9` kN (E4), loading each spring line to a safe `19.90%` of MBL (E5)!
| OCIMF MEG4 Berth Mooring KPI (MBL=1,150 kN: Normal 22 m/s, 1.6 m/s, 4 Lines vs Squall 32/2.2, 2 Lines) | Formula | Verified Output |
|---|---|---|
| Aerodynamic Wind Load Fw (kN) | (0.5 * 1.225 * Cw * Aw * Vw^2) / 1000 | 352.5 kN (745.7 kN @ 32 m/s squall) |
| Tidal Current Drag Fc (kN) | (0.5 * 1025 * Cc * Ac * Vc^2) / 1000 | 443.5 kN (838.4 kN @ 2.2 m/s spring ebb) |
| Total Environmental Load (kN) | Wind_Force_kN + Current_Force_kN | 795.9 kN (1,584.1 kN @ squall) |
| Peak Hawser Tension (% MBL) | (((1.15 * F_tot) / N_lines) / MBL) * 100 | 19.90% (79.21% > 60% BRAKE RENDER!) |
OCIMF MEG4 Wind + Shallow-Water Current Drag & Hawser %MBL Formula
Validate `Wind_Speed V_w >= 0` m/s, `Wind_Area A_w > 10` m², `C_w` in `[0.2, 2.0]`, `Current_Speed V_c >= 0` m/s, `Submerged_Area A_c > 10` m², `C_c` in `[0.1, 3.0]`, integer `Lines N >= 1`, and `MBL > 50` kN!
=LET(vw_m, B2, aw_m, B3, cw_d, B4, vc_m, B5, ac_m, B6, cc_d, B7, nl_c, B8, mb_k, B9, fw_k, (0.5 * 1.225 * cw_d * aw_m * (vw_m ^ 2)) / 1000, fc_k, (0.5 * 1025 * cc_d * ac_m * (vc_m ^ 2)) / 1000, IF(OR(vw_m < 0, aw_m <= 10, cw_d < 0.2, cw_d > 2, vc_m < 0, ac_m <= 10, cc_d < 0.1, cc_d > 3, nl_c < 1, mb_k <= 50), "Invalid Mooring Input", ROUND((((1.15 * (fw_k + fc_k)) / nl_c) / mb_k) * 100, 2)))32 m/s Squall + 2.2 m/s Spring Tide on 2 Slack-Mismanaged Lines Brake-Render Check
Hit a `32` m/s thunderstorm gust with `2.2` m/s spring tide while `2` slack lines leave only `N = 2` taut springs carrying surge (`B2 = 32`, `B5 = 2.2`, `B8 = 2`): Total Force E4 doubles to `1,584.1` kN and Line Stress E5 spikes to **`79.21%` of MBL**—exceeding both the `55%` SWL ceiling and `60%` winch brake render point, causing vessel drift that triggers emergency loading-arm `ERS` disconnect!
=IF(ISTEXT(E5), E5, LET(fw_k, (0.5 * 1.225 * B4 * B3 * (B2 ^ 2)) / 1000, fc_k, (0.5 * 1025 * B7 * B6 * (B5 ^ 2)) / 1000, ROUND(fw_k + fc_k, 1)))Try the example
Use the original values or change them to test your understanding.