A docked ship still needs power for lighting, pumps, refrigerated ("reefer") containers and crew systems — its hotel load. Without shore power it burns diesel in its auxiliary generators the whole time it's berthed. Cold ironing (shore power / Alternative Maritime Power) lets it shut those engines down and plug into the local grid instead, exactly like an aircraft on stand or an EV at a charger.
Energy at berth: E = P_load · t_dwell (kWh)
Baseline (all-diesel) emissions:
M_diesel = E · f_diesel (kg CO2)
With shore power at adoption fraction f:
M_mixed = E · [f·g_grid + (1−f)·f_diesel] / 1000
CO2 avoided: ΔM = M_diesel − M_mixed = E · f · (f_diesel − g_grid) / 1000
where f_diesel ≈ 750 gCO₂/kWh is a typical marine auxiliary-diesel-generator emission factor and g_grid is the local electricity grid's carbon intensity (a coal-heavy grid can erase most of the benefit; a hydro/wind/nuclear-heavy grid nearly eliminates dockside emissions).
This 2D view adds a live emissions-timeline panel: it integrates the diesel-baseline rate and the actual mixed rate minute-by-minute across the whole dwell period, so the shaded gap between the two curves is the CO₂ avoided — the same quantity the readout box reports, just drawn as an accumulating area instead of a single number.
- Hotel load — how much power the ship's onboard systems draw while berthed.
- Dwell time — how long the ship stays connected at the berth (also sets the timeline's horizontal scale).
- Shore power adoption — the fraction of dwell time actually plugged into shore power rather than running the diesel gensets.
- Grid carbon intensity — the CO₂ per kWh of the local electricity supply; this is what shore power is actually competing against.
- Timeline speed — how fast the simulated dwell period plays out on screen; it does not change any of the physics, only the pace you watch it at.
Real ports (Los Angeles, Long Beach, Rotterdam, Shanghai) now mandate or incentivize cold ironing at container and cruise berths specifically because it removes near-shore diesel exhaust — the single largest source of port-adjacent air pollution — without needing the ship's engine technology to change at all.