Two Days After the Houthi Blockade Announcement, the Red Sea Split in Two

The Houthis declared a naval blockade against Saudi Arabia on July 20, escalating threats across the Red Sea corridor while Iranian forces struck three tankers in the Strait of Hormuz within 48 hours.

That ambiguity is doing real work. Within a day, Windward tracked the market splitting into two opposite flows: commercial tonnage pulling back from Bab al-Mandeb, and sanctioned Iranian traffic pushing into it.

Commercial Tankers Are Turning Around

Five tankers heading toward Bab al-Mandeb reversed course as blockade threats rose. Four were carrying Saudi-origin cargo: crude, gasoil, and naphtha, totaling an estimated 3.84 million barrels, per Vortexa. Four turned back inside the Red Sea; one u-turned outside it, in the Gulf of Aden. The diversions span both of Saudi Arabia’s western export terminals, Yanbu and Jizan.

The spread is the signal. The mix of cargoes and destinations points to broad commercial risk-avoidance, not a single-buyer or single-terminal event. And the vessel that reversed on a ballast China–Canada leg as far out as the Gulf of Aden says owners are treating the wider Bab al-Mandeb approach as the risk zone, not just the Red Sea proper.

The pattern includes large hulls. The VLCC Xin Long Yang (IMO 9761463) — a Singapore-flagged, 333-meter crude oil tanker managed by Cosco Shipping Energy — departed Yanbu southbound and reversed course over a Houthi threat, still declaring Qinzhou, China.

Not everyone is turning around. Three Saudi-linked VLCCs continued crossing or approaching the strait despite the threat, and three Saudi-flagged VLCCs went dark on July 20. The economics explain the risk appetite: full avoidance via the Cape of Good Hope roughly doubles voyage length and adds an estimated $2–2.5 million in cost per transit.

The aggregate flow shows the imbalance. Windward tracked 26 vessels crossing into the Red Sea against 17 outbound on July 20, with inbound crossings swinging from a mid-July peak near 45 to below 15 within days.

One Vessel Went the Other Way

Against that outflow, an OFAC-sanctioned, Iranian-flagged container vessel entered Yemen’s exclusive economic zone and crossed Bab al-Mandeb on July 21. The first Red Sea activity anywhere in its available tracking history, one day after the blockade announcement.

The move breaks a six-month pattern confined entirely to the Persian Gulf–China corridor. The vessel carries active OFAC designations under the Iran and NPWMD programs, a high smuggling risk score, and a behavioral record that includes nine AIS dark gaps, seven loitering instances, and a past identity-manipulation event. Reporting has linked it to suspected rocket-fuel-material cargoes.

A vessel with that profile making its first-ever transit of a Houthi-declared blockade zone the day after the declaration is hard to square with routine scheduling. Windward assesses the transit as a potential indicator of Iran–Houthi coordination, whether weapons movement, a tacit safe-passage arrangement, or deliberate exploitation of reduced traffic and scrutiny in the corridor.

The Pressure Is Coming From Hormuz

The Red Sea shift is downstream of the Strait of Hormuz, where the southern corridor has fallen to a near-standstill under the standing IRGC closure declaration and reinstated blockade of Iranian-port traffic. Windward logged 11 inbound and 4 outbound Hormuz transits on July 20, all in the northern corridor, with 3 of the 11 inbound and 3 of the 4 outbound vessels running dark.

The strikes are shaping behavior. Iranian forces hit two Greek-operated tankers near Kumzar, Oman on July 20, then a Kuwaiti state-owned tanker near Limah overnight — the third vessel struck in the southern corridor in a day. All three were transiting AIS-dark at the time of attack.

Meanwhile, the staging picture around the strait is thickening. Twenty-one tankers were assessed congregated at Iran’s Kuh-e-Mubarak anchorage, nine running fully dark and seven OFAC-designated. Across the Gulf of Oman, fraudulent and high-risk-flagged vessels remain concentrated at staging hubs, with the largest single cluster — 44 vessels — massed at the Khor Fakkan/Fujairah OPL anchorage.

What to Watch

Three things over the coming days. First, whether the Bab al-Mandeb inbound/outbound gap widens. A sustained imbalance would signal the corridor is being ceded to risk-tolerant traffic. Second, the post-transit destination of the sanctioned Iranian container vessel, which would show whether its crossing was a through-transit or a Red Sea delivery. Third, whether the Saudi-flagged VLCCs that went dark on July 20 resurface, and where.

Windward is tracking the corridor in real time. Follow the live picture on the Strait of Hormuz and Red Sea tracker.