This is the side-view companion to the 3D Ocean Cleanup Boom sim: instead of the top-down herding funnel, it models the physics the 3D version only approximated — why an object's windage speed is what it is, and why a boom stops some debris but not all of it, from first principles.
Leeway (windage) from a drag force balance. A floating object sits at an equilibrium draft set by Archimedes' principle, exposing a freeboard area to wind and a submerged area to water. Its steady drift speed relative to the current is set by the point where wind drag on the freeboard equals water drag on the draft:
draft = ρ*·d, freeboard = (1−ρ*)·d (ρ* = object density ÷ water density)
½ρ_air·Cd·A_exp·V_wind² = ½ρ_water·Cd·A_sub·V_lee²
k = V_lee / V_wind = √[ (ρ_air/ρ_water) · (1−ρ*)/ρ* ]
The object's size d cancels out of k — windage depends only on how buoyant the object is (its freeboard-to-draft ratio), not its raw size, exactly as in real search-and-rescue leeway drift models. A foam fragment (ρ* ≈ 0.03) has roughly 5× the windage coefficient of a waterlogged plank (ρ* ≈ 0.9). Verified numerically: plugging k back into the original force-balance equation reproduces F_wind = F_water to machine precision for every ρ* tested.
Relative to the boom (towed at v_tow through ambient current v_current):
v_rel = (v_current + k·v_wind) − v_tow
When v_rel < 0 the boom overtakes the debris and herds it toward the net; if wind pushes windage high enough that v_rel ≥ 0 mid-funnel, the debris outruns the boom and escapes out the mouth.
Skirt depth vs. draft — a different escape route than the 3D model's mesh gap. The physical curtain hangs from the surface down to a fixed skirt draft Db. Any debris whose own equilibrium draft exceeds Db simply rides too low in the water to be blocked and slips underneath, regardless of its size — a distinct, buoyancy-driven failure mode from the 3D sim's mesh-gap size threshold, and the reason real containment booms specify a minimum skirt draft for the debris class they target.
Capture efficiency = captured ÷ (captured + slipped + outran), counted only among debris that reached the boom's capture zone. Time is compressed ×15 for visibility; ambient current is held at 0.15 m/s.