The 18-Mile Width and the 2.5-Mile Perim Island Channel: How the Bab el-Mandeb Strait's Physical Constraints Dictate Red Sea Shipping

Houthi forces have established operational control over the Bab el-Mandeb Strait, effectively closing the world's second-largest oil chokepoint to hostile commercial transit. The seizure has immediately disrupted global energy markets, with diesel prices spiking to $6 per gallon amid a developing global energy crisis.[3]

While the political and military dimensions of the blockade dominate international responses, the strait's vulnerability is fundamentally dictated by its physical geography. The Bab el-Mandeb—Arabic for "Gate of Tears"—connects the Red Sea to the Gulf of Aden and the Indian Ocean, serving as the unavoidable southern gateway to the Suez Canal.[1]

At its narrowest point, the waterway measures just 18 miles (29 kilometers) across, separating the Republic of Yemen on the Arabian Peninsula from Djibouti and Eritrea on the Horn of Africa. However, this 18-mile figure overstates the actual navigable space available to modern commercial shipping.[1]

The strait is physically divided by Perim Island, a volcanic rock formation also known as Mayyun, which sits roughly 2 miles off the Yemeni coast. This island splits the Bab el-Mandeb into two distinct channels, completely altering the maritime traffic pattern.[1]

The eastern channel, known as Bab Iskender or Alexander's Strait, runs between Perim Island and the Yemeni mainland. It is only 2 miles (3.2 kilometers) wide and has a maximum depth of roughly 30 meters. Due to its shallow waters and treacherous currents, this channel is entirely unsuitable for deep-draft commercial vessels.[1]

Consequently, all major international shipping—including Very Large Crude Carriers (VLCCs) and massive container ships—must use the western channel, known as Dact-el-Mayun. While this western passage is 16 miles (26 kilometers) wide, the safe, deep-water corridor is significantly narrower.[1]

To prevent collisions in this congested space, the International Maritime Organization enforces a Traffic Separation Scheme (TSS). This system restricts vessels to two dedicated lanes—one for northbound traffic entering the Red Sea, and one for southbound traffic exiting into the Gulf of Aden.

Each of these designated transit lanes is exactly 2.5 miles (4 kilometers) wide. A buffer zone separates the two lanes to prevent head-on collisions between vessels that can require miles to come to a complete stop.

This 2.5-mile constraint is the structural reality that makes the Bab el-Mandeb so susceptible to asymmetric warfare. A commercial vessel confined to a narrow, predictable corridor cannot take evasive action without risking grounding or collision.

Under the 1982 United Nations Convention on the Law of the Sea (UNCLOS), the Bab el-Mandeb is subject to the regime of "transit passage." This legal framework guarantees all ships and aircraft the right of continuous and expeditious transit through straits used for international navigation.

However, as legal scholars at the NCLOS Blog noted in their 2021 analysis of the strait, the standard passage regime is severely tested by persistent maritime security threats. The legal right to transit means little when physical safety cannot be guaranteed.

The situation is further complicated by the collapse of central authority in Yemen. The fragility of the maritime order in the Bab el-Mandeb is directly tied to international law confronting the absence of a functional state apparatus on the strait's eastern shore.[2]

With Houthi forces now controlling the adjacent coastline and Perim Island itself, the 2.5-mile inbound and outbound lanes are well within the range of basic coastal defense cruise missiles, aerial drones, and fast attack craft.[3]

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The economic consequences of this geographic bottleneck are immediate and severe. When the 2.5-mile lanes are closed, ships must abandon the Red Sea route entirely and detour around the Cape of Good Hope at the southern tip of Africa.[3]

This rerouting adds approximately 3,500 nautical miles and 10 to 14 days of transit time to a standard journey between Asian manufacturing hubs and European consumer markets, burning hundreds of tons of additional marine fuel per vessel.[3]

Because direct quotations from maritime authorities operating within the strait are currently unavailable due to the communications blackout surrounding the seizure, analysts are relying on satellite tracking and geographic data to assess the blockade's mechanics.

What that data shows is a complete structural dependency. The global supply chain relies on the Suez Canal, but the Suez Canal relies entirely on the physical viability of a 2.5-mile strip of water passing a volcanic island off the coast of Yemen.[1]