Ground effect is real physics: when a wing flies within about one chord-length of a surface, induced drag collapses because the wingtip vortices can't fully form. The lift-to-drag ratio jumps 40–100%. The Soviets exploited this with the Caspian Sea Monster (KM ekranoplan): 380 tonnes, 500 km/h, cruising 3–5 meters above the water. So: what if trans-Atlantic freight flew this way instead of at 35,000 feet?

The fuel math is genuinely tempting. A Boeing 747-8F carries ~140 tonnes of payload 14,000 km, burning around 12 L of jet fuel per km — roughly 85 g fuel per tonne-km. Ground effect roughly doubles cruise efficiency (L/D of ~25 vs. ~17 for a 747). Add: no climb to altitude (a 747 burns ~15 tonnes just getting to cruise), no thin-air compressor bleed penalties, no cabin pressurization mass. A 500-km/h ekranoplan freighter could plausibly hit 40–50 g/tonne-km — about 45% less fuel per tonne of cargo.

But sea state kills you. Ground effect requires h/c < 0.1 (altitude under 10% of wing chord). For a KM-scale ekranoplan with a 10-meter chord, that's flying no more than 1 meter above the wave crests. North Atlantic significant wave height in winter averages 4 m and exceeds 6 m about 15% of the time. You simply cannot skim a 4-meter sea at 500 km/h — you'd auger in on the first swell face. Solution: fly higher, but at 20 m altitude the ground-effect bonus evaporates and you're just a very slow airplane with a bad L/D.

The reroute penalty: To dodge storms, you'd add ~20% to great-circle distance. NYC to Lisbon is 5,400 km direct; realistic ekranoplan routing pushes it to ~6,500 km, and at 500 km/h that's 13 hours vs. 6.5 hours for a 747F. Cargo owners pay premium for speed; ekranoplans capture the middle market between ships (11 days) and jets (7 hours).

Structural scaling is brutal. Wing loading for ground effect wants to be low (~300 kg/m²), so a 500-tonne freighter needs ~1,700 m² of wing — a 90-meter span. That's larger than an An-225. Bird strikes at wavetop altitude are relentless, and salt spray ingestion into turbofans requires either massive inlet filtering (parasitic drag) or turboprops with corrosion-hardened compressors. The Soviets used eight Kuznetsov turbojets on the KM partly for takeoff blowing under the wing (PAR: power-augmented ram) — you need extra engines just to get unstuck from the water.

Where it actually works: Short, protected routes with dense freight demand. Think Shanghai–Osaka (1,800 km, mostly sheltered), or Baltic Sea cargo hops, or Caribbean island logistics. A 200-tonne ekranoplan on those routes beats both containerships (on time) and 767 freighters (on cost per tonne) with a probably-defensible dispatch reliability of 85%.

The physics doesn't say never — it says not the North Atlantic in February.