How the U.S. blockade and Iranian controls are disrupting Strait of Hormuz shipping

A shipping-law analysis described the practical situation less as a universal closure than as a route that is closed for some traffic and still open for other traffic ^[4]. That distinction matters commercially: a vessel may still be able to physically transit Hormuz, especially if it is not entering or leaving Iran, while other voyages face delays, clearance uncertainty, security risk, or sanctions exposure that can make passage impractical ^{[1][6][8][14]}.

What the U.S. blockade covers

U.S. Central Command said its forces would begin blocking maritime traffic entering and exiting Iranian ports and coastal areas on April 13, 2026, at 10 a.m. ET, and that the blockade would apply to vessels of all nations using Iranian ports ^[14]. CENTCOM also said it would not impede freedom of navigation for vessels transiting the Strait of Hormuz to and from non-Iranian ports ^[14].

That makes the U.S. measure targeted at Iranian maritime access, rather than an announced blanket shutdown of the strait itself ^[14]. In practice, however, even a targeted blockade can disrupt regional shipping when it intersects with Iranian controls and the need for vessels to move through a narrow Gulf chokepoint.

How Iranian controls widen the disruption

The Iranian side of the crisis is broader in practical effect. A U.S. Maritime Administration advisory says Iran continues to threaten and conduct strikes on commercial vessels transiting the Persian Gulf, Strait of Hormuz, and Gulf of Oman, and says the risk of Iranian attacks against commercial shipping remains high in those areas ^[1]. The same advisory notes that Iranian forces have historically used small boats and helicopters in boarding operations and have attempted to force commercial vessels into Iranian territorial waters ^[1].

Separate reporting says Iran created a government agency to vet and tax vessels seeking passage through the Strait of Hormuz, raising concerns as hundreds of commercial ships were described as bottled up in the Persian Gulf and unable to reach the open sea ^[6]. Another report said the U.S. blockade of Iranian ports prompted Tehran to maintain its own restrictions on the strait ^[9].

The main commercial impacts

1. Delays, turnbacks, and backlogs

The clearest impact is operational. Ship-tracking reports counted extremely low daily transit numbers in late April, while Associated Press reporting carried by Audacy said hundreds of commercial ships were bottled up in the Persian Gulf ^[5][6][9]. The Los Angeles Times also reported that the U.S. naval blockade of Iranian ports had forced 48 commercial vessels to turn back by May 2 ^[8].

For charterers and operators, those reports point to a route where schedule reliability has broken down. Vessels may wait, attempt limited passage, turn back, or avoid the area depending on cargo, flag, port call, insurer, and sanctions exposure.

2. Higher security risk for crews and cargo

The security risk is not theoretical. The U.S. Maritime Administration advisory says Iran continues to threaten and conduct strikes on commercial vessels in the Persian Gulf, Strait of Hormuz, and Gulf of Oman, and that risks remain high ^[1]. That changes voyage planning from a normal routing decision into a threat-assessment problem involving possible attack, boarding, forced diversion, or escalation ^[1].

3. Marine-insurance and shipping-law uncertainty

The legal and insurance picture is complicated because operators face overlapping controls. A shipping-law and marine-insurance analysis described the Gulf situation as one involving two conflicting approaches: Iranian forces asserting control over passage through the Strait of Hormuz, and the U.S. military announcing a blockade of maritime traffic entering and exiting Iranian ports ^[4].

That does not establish one universal insurance surcharge for every vessel. The available sources support a narrower conclusion: risk and legal uncertainty have increased, and the cost or insurability of a voyage will depend on the vessel, cargo, route, port call, insurer, and contract terms ^[1][4].

4. Sanctions exposure around payments to Iran

A major compliance problem is whether a company can pay Iran for clearance or safe passage. The Los Angeles Times reported that the U.S. warned shipping companies they could face sanctions for paying Iran to ensure safe passage through the Strait of Hormuz ^[8]. That warning sits uneasily beside reporting that Iran has moved to vet and tax vessels seeking passage ^[6].

The result is a difficult commercial bind: a ship may face Iranian demands or controls to move through the strait, while also facing U.S. sanctions risk if it pays Iran for that passage ^[6][8].

5. Disruption to oil and LNG cargo planning

Hormuz matters because it is a major energy chokepoint. Reporting in the source set says the strait had typically handled roughly one-fifth of the world’s oil and liquefied natural gas supply ^[9]. When traffic falls to crisis levels, the effect reaches beyond Gulf ports: tanker scheduling, cargo availability, and market expectations can all be affected by uncertainty over whether vessels can enter or leave the Gulf ^[5][9].

Which vessels are most affected?

The most directly affected vessels are those entering or leaving Iranian ports, because that is the stated focus of the U.S. blockade ^[14]. Ships serving non-Iranian Gulf ports are not supposed to be blocked by the U.S. under CENTCOM’s stated policy, but they still face Iranian threat warnings, reported controls, and passage uncertainty around the strait ^[1][6][14].

Vessels already inside the Persian Gulf may be especially exposed if they need to exit through Hormuz but cannot secure a safe, legally compliant, and commercially viable passage ^[6][8]. Energy cargoes are also highly exposed because of the strait’s role in oil and LNG flows ^[9].

Bottom line

The Strait of Hormuz is not fully closed, but it is no longer functioning like a normal, predictable shipping lane. The strongest reading of the available evidence is a de facto partial closure: some vessels continue to transit, while U.S. restrictions on Iran-linked port traffic and Iranian controls, threats, and reported vetting measures have sharply degraded commercial movement ^{[1][4][5][6][9][14]}.

For shipping companies, the practical consequences are delays, vessel backlogs, turnbacks, higher security scrutiny, marine-insurance and legal uncertainty, sanctions-sensitive payment decisions, and disrupted energy-cargo planning ^{[1][4][6][8][9]}.