Maritime Chokepoints: Canals and Straits

A maritime chokepoint is a canal or strait through which a large share of a trade flow must pass, because the alternative route is so much longer or more dangerous that almost every ship accepts the fee, the queue or the risk. The test has two parts and both must hold: traffic concentrates, and no cheap substitute exists. Two governance families divide the set. A canal is owned by an authority that sets the toll and can refuse a transit, under a treaty regime such as the Constantinople Convention of 1888 at Suez. A strait is governed by its littoral states under Part III of the United Nations Convention on the Law of the Sea, carries no transit fee, and cannot lawfully be closed to a transiting ship. The physical dimensions of each passage produce the named size classes the world fleet is built to: Panamax, Panamax Plus and Neopanamax at Panama, Suezmax at Suez, Malaccamax at Malacca. This article covers the taxonomy, the comparative limits and the governance contrast; the Panama Canal , Suez Canal , Strait of Malacca and Danube River basin articles carry the lock geometry, tariff history and per-passage detail.

What a maritime chokepoint is

A chokepoint concentrates a large share of traffic into a narrow corridor with no easy substitute, and the strategic weight comes from the absence of that substitute rather than from the narrowness. A passage everyone can avoid cheaply is not a chokepoint. A passage that forces a detour of some 3,200 nautical miles when it closes is, and UNCTAD measured the fleet-wide consequence of exactly that when Red Sea traffic rerouted: the Cape of Good Hope detour added approximately 30 percent to voyage lengths, contributing to an estimated 11 percent increase in container TEU-mile demand in 2024.

Canal and strait: who owns the passage

The first distinction is whether the passage is artificial or natural, and almost everything else follows from it. A canal is cut through land and run by an authority that sets the transit fee, rations the daily slots and can refuse a transit: the Panama Canal Authority and the Suez Canal Authority are the two large examples. A strait is a natural narrowing governed by its littoral states under UNCLOS Part III, and it carries no transit fee, because Part III confers no charging power on anyone.

That ownership difference decides how each passage fails. A canal authority can raise a toll, cut slots in a drought or close for maintenance, and the market must respond within its own commercial logic. A strait has no toll to raise and fails through conflict, armed robbery or a single grounded ship, with no authority positioned to manage the recovery. The Strait of Malacca has no counterpart to the Panama Canal Authority, which is why its safety and security arrangements had to be built as cooperative instruments among four states and IMO rather than issued by an owner.

Lock canal and sea-level canal

The second distinction applies only to canals and it decides both the size limit and the drought exposure. A sea-level canal is a single open cut joining two seas of near-equal mean level, with no lift. The Suez Canal is the case: no lock chambers, so no chamber geometry caps beam or length, and the binding constraint is the dredged depth together with the Authority’s beam-versus-draught table.

A lock canal crosses high ground by lifting ships into a summit reach. The Panama Canal raises ships 85 feet, about 26 m, into Gatun Lake, because the Isthmus of Panama could not be cut at sea level through the Continental Divide. That capability costs two things. Each chamber is a fixed box whose width, length and sill depth cap the largest ship that fits, and that cap is what created the Panamax and Neopanamax classes. And every lockage spends fresh water: the Panama Canal Authority states that vessels transiting the canal use 52 million gallons of fresh water in every transit, which is why a dry year forces draft cuts and slot reductions and why the same weather cannot touch Suez at all.

The Panama Canal Authority’s original lock chambers are all the same size. In its own words, all lock chambers have the same 110 by 1,000 feet dimensions, that is 33.53 m by 304.8 m, and they are built in pairs so two lanes run side by side: three steps at Gatun, one at Pedro Miguel and two at Miraflores, six pairs and 12 chambers in all. That pairing is the canal’s redundancy, and it is why a chamber can be taken out of service without closing the waterway.

The four physical limits that gate a transit

A ship clears a chokepoint only if it is inside four independent limits: beam, length overall, draught and air draft. Each is set by a different feature of the passage, and the one that binds differs from passage to passage. That is the single most useful thing to know about chokepoints, because it explains why the size classes are a hierarchy of constraint rather than a ranking by size.

Beam and length overall

Beam is the side-to-side limit, set by lock chamber width on a lock canal and by dredged channel and traffic-lane width elsewhere. It is the least forgiving of the four, because it cannot be reduced by discharging cargo and cannot be altered after the ship is built. Length overall is capped by chamber length on a lock canal and by maneuvering room elsewhere, and the Panama Canal Authority measures it including the bulbous bow.

At Suez, where no chamber exists, the Authority still publishes a beam limit: 254 ft 3 in, or 77.5 m, above which a transit is by special request. So the common statement that a sea-level canal has no width limit is wrong as a matter of the published rules, even though the limit sits far above anything a lock canal can accept.

Draught, under-keel clearance and the fresh-water correction

Draught is limited by sill depth in a lock, dredged depth in a sea-level canal and charted depth in a strait, and it is the most forgiving limit because cargo can be left behind. Two complications attach to it.

The first is density. Fresh water is less dense than sea water, so a ship floats deeper in it, and a draught measured at sea does not transfer to a canal. The Panama Canal Authority quotes every draught limit on a tropical fresh water basis and states the density it works to as 0.9954 g/cc at 29.4 degrees Celsius. The correction belongs in the loading calculation before the ship sails.

The second is under-keel clearance , which converts a charted depth into a usable draught. In the Straits of Malacca and Singapore the rule is regulatory rather than a matter of local practice: IMO Assembly Resolution A.375(X) of 14 November 1977 defines a deep draught vessel as one of 15 m draught or more, and requires that deep draught vessels and very large crude carriers allow for an under-keel clearance of at least 3.5 m at all times during the entire passage. The same resolution directs deep draught vessels to the designated Deep Water Route and advises a speed of not more than 12 knots over the ground. The squat effect is why that speed advice sits alongside the clearance rule rather than separately from it.

Draught limits also move with the water. The Panamax figure of 12.04 m applies at a Gatun Lake level of 24.01 m or higher and the Neopanamax figure of 15.24 m at a lake level of 25.91 m or higher. Below those levels the Panama Canal Authority reduces the authorized draft by advisory, in decrements of 15.24 cm, with three weeks’ notice where possible. Ships already loaded when a reduction is promulgated are waived; ships loading afterward are held to a 15.24 cm tolerance.

Air draft and the fixed bridge

Air draft is the height from the waterline to the highest fixed point, and it is the limit a ship cannot reduce by discharging cargo. A vessel can clear every chamber and still be turned back.

At the Panama Canal the limit is 57.91 m (190 ft), measured from the waterline to the vessel’s highest point, at any state of the tide, for transit or for entry to the Port of Balboa. With prior permission from the Transit Operations Division Executive Manager, up to 62.5 m (205 ft) is possible case by case at low water at Balboa. The Panama Canal Authority attributes the restriction to tide, swell and surge and to maintenance equipment suspended beneath the bridge at Balboa, which is worth stating precisely: the governing number is an operational limit set by the Authority, not a published clearance figure for the Bridge of the Americas, and the two are frequently confused.

Which limit binds where

Sources: Panama Canal Authority OP Notice to Shipping N-1-2026; Suez Canal Authority Rules of Navigation; IMO Assembly Resolution A.375(X); Turkish Straits Maritime Traffic Regulation 2019; Wasserstrassen- und Schifffahrtsamt Nord-Ostsee-Kanal. Effective 19 August 2026.

Two rows in that table earn their place by being empty. Hormuz and Bab el-Mandeb impose no physical size limit at all, which is why no size class is named after either, and why the constraint at both is entirely political and military rather than hydrographic.

The chokepoint size classes

Four size classes take their names from chokepoints, and they do not have equal standing. Panamax, Panamax Plus and Neopanamax are defined by the Panama Canal Authority in published notices and change when the Authority changes them. Suezmax and Malaccamax are market conventions with no issuing authority behind them. Treating all of them as equally official is the most common error made about the subject.

The classes the Panama Canal Authority actually defines

OP Notice to Shipping N-1-2026, effective 1 January 2026, carries three categories.

Panamax covers vessels of 30.48 m beam or more complying with 294.13 m by 32.31 m by 12.04 m tropical fresh water draft. Alongside that definition sit two operational numbers often mistaken for it: the maximum length overall accepted is 289.6 m, except passenger and container ships at 294.43 m, and beams from 32.4 m up to 32.9 m may be permitted with prior approval where the deepest point of immersion does not exceed 11.3 m. The 32.31 m beam against a 33.53 m chamber leaves under 60 cm of clearance a side.

Panamax Plus covers Panamax vessels authorized for tropical fresh water drafts above 12.04 m and up to 15.24 m and approved for the new locks. It exists because the Panamax and Neopanamax pair does not describe every ship the canal handles, and the reservation system permits one Panamax Plus vessel per transit date.

Neopanamax is 370.33 m by 51.25 m by 15.24 m tropical fresh water draft. Two figures in wide circulation are real Panama Canal Authority limits attached to the wrong class. The maximum beam of 49.00 m applies to non-self-propelled vessels, meaning dead tows, not to a self-propelled ship, which is measured against 51.25 m. The maximum length of 366.0 m applies to integrated tug-barge combinations, while 400.0 m is the aggregate limit for non-self-propelled vessels transiting with tugs. A self-propelled commercial vessel is measured against 370.33 m including the bulbous bow.

The classes nobody defines

Suezmax has no Suez Canal Authority definition. As the market uses the term it means the largest crude tanker that transits fully laden, in practice about 274 to 285 m in length overall, 48 to 50 m in beam, around 16 m laden draught and 120,000 to 160,000 DWT. What the Authority publishes instead is a beam-versus-draught envelope in Tables 1 and 2 of its Rules of Navigation, ballast and loaded, stated against the Tropical Load Line, plus the 77.5 m maximum beam.

That envelope is the source of the most persistent confusion on the subject. The canal’s headline maximum permissible draught of about 20.1 m (66 ft) and the roughly 16 m working laden draught of a Suezmax tanker are both correct and describe different ships: a narrower vessel may sit deeper, a wider one must sit shallower. Neither figure is the whole rule, and a route study that treats the 20.1 m as available to a 50 m beam hull has misread the table. The canal’s practical length ceiling of about 400 m belongs to the canal, not to the class: the Ever Given, at 399.94 m, is a container ship, not a Suezmax tanker.

Malaccamax rests on the A.375(X) under-keel clearance rule applied against the controlling charted depth. The clearance requirement is firm and published; the controlling depth figure is not published by any littoral-state authority in a form this article can cite, so the honest statement is the rule and its input rather than a headline draught presented as official.

Source: Panama Canal Authority OP Notice to Shipping N-1-2026, 1 January 2026, and IMO Assembly Resolution A.375(X), 14 November 1977. Suezmax figures are market usage and carry no authority definition.

The table reads as a hierarchy of constraint. A Neopanamax ship is longer and beamier than a Panamax but shallower-drafted than a Suezmax, because chamber width binds at Panama while depth binds at Suez and Malacca. The Malaccamax draught is the deepest of the set, since a natural strait can be far deeper than any lock sill. A naval architect building for a trade that crosses one of these passages builds to the class limit with a margin, and the container ship size classes , bulk carrier size classes and tanker size classes articles trace how each fleet settled where it did.

Governance: who controls a passage

A canal is owned and run by an authority that sets the fee and can refuse a transit; a strait is governed by its littoral states under UNCLOS Part III, carries no fee, and cannot lawfully be closed to a transiting ship. Four governance models cover every passage in this article, and knowing which one applies tells a practitioner whether anyone can charge them or turn them away.

Transit passage under UNCLOS Part III

Transit passage is the right of continuous and expeditious passage through a strait used for international navigation, in Part III Section 2 of the United Nations Convention on the Law of the Sea. Article 44 provides that states bordering straits shall not hamper transit passage and that there shall be no suspension of transit passage. That is a stronger right than innocent passage in the territorial sea, which may be suspended temporarily.

The right is not unlimited, and the common summary that a littoral state “cannot refuse a lawful transit” understates its powers. Article 42(1) allows bordering states to legislate on four subjects: navigational safety and traffic regulation under Article 41, pollution discharge, fishing by fishing vessels, and loading or unloading contrary to customs, fiscal, immigration or sanitary law. Article 42(4) obliges foreign ships to comply. Article 233 allows enforcement measures where a violation under Article 42(1)(a) or (b) causes or threatens major damage to the marine environment of the strait. Under Article 34 the littoral states retain sovereignty over the waters, exercised subject to Part III.

Traffic management runs through IMO rather than unilaterally. Article 41 allows sea lanes and traffic separation schemes to be designated only after referring proposals to the competent international organization, which may adopt only such schemes as are agreed with the states bordering the strait. That is why ships’ routeing measures are IMO instruments, and why the traffic separation scheme in the Strait of Hormuz was proposed by Iran and Oman and adopted by IMO rather than imposed by either state.

Where transit passage does not apply

Three carve-outs matter, and each has a live example.

Article 36 removes Part III entirely where a route of similar convenience through the high seas or an exclusive economic zone exists through the strait. Article 38(1) removes transit passage where a strait is formed by an island of a bordering state and its mainland and a similar route exists seaward of the island, with Article 45 substituting non-suspendable innocent passage. Bab el-Mandeb engages that test directly, because the Yemeni island of Perim divides it into two straits. Article 35(c) preserves the legal regime in straits regulated by long-standing international conventions in force specifically relating to them, which is what keeps the Montreux Convention operative over the Turkish Straits .

A fourth complication is party status rather than a carve-out. Iran signed the Convention on 10 December 1982 and has never ratified it, and its declaration on signature states that only states parties shall benefit from the contractual rights created in the Convention, naming the right of transit passage under Article 38 first among its examples. Oman ratified on 17 August 1989 with a declaration that Articles 19, 25, 34, 38 and 45 do not preclude a coastal state from taking measures necessary to protect its interest of peace and security. Many maritime states treat transit passage as customary international law binding regardless of ratification. That disagreement is unresolved, and it is one of the few points in this subject where the position is genuinely unsettled rather than merely complicated.

A treaty regime over a strait: Montreux and the Turkish Straits

The Convention Regarding the Regime of the Straits was signed at Montreux on 20 July 1936 and entered into force on 9 November 1936, having been applied provisionally from 15 August 1936. Article 2 provides that in time of peace merchant vessels shall enjoy complete freedom of transit and navigation in the Straits, by day and by night, under any flag and with any kind of cargo, without any formalities, and that pilotage and towage remain optional.

Turkey may charge, but only what Annex I authorizes and only for services rendered. Article 2 provides that no taxes or charges other than those authorized by Annex I shall be levied on vessels passing in transit without calling at a port. Annex I sets a tariff per ton of net register tonnage in gold francs under three heads: sanitary control stations at 0.075, lighthouses and light and channel buoys at 0.42 up to 800 tons and 0.21 above, and life saving services at 0.10. It caps them at what is necessary to cover the cost of the services plus a reasonable reserve, and requires any reduction to be applied without distinction based on flag.

The Convention imposes a separate and far more restrictive regime on warships in Articles 8 to 22, including prior diplomatic notification, aggregate tonnage caps, a stay limit in the Black Sea, and Turkish discretion under Articles 20 and 21 when Turkey is belligerent or considers itself threatened with imminent danger of war.

Montreux does not give Turkey power to regulate the flow of commercial traffic in peacetime, and the frequent statement that it does is wrong. The only merchant-traffic directions the Convention permits, meaning daylight entry, a route indicated by the Turkish authorities and compulsory pilotage without charge, arise under Articles 5 and 6, which apply in war or on imminent danger of war. The suspension and one-way traffic powers exercised in practice come from Turkish national law, currently the Turkish Straits Maritime Traffic Regulation made by Presidential Decision No. 1426 of 14 August 2019, which replaced the 1998 regulation. Under its Article 37, when visibility anywhere in the Istanbul Strait falls to 1 mile or below, traffic is kept open in one direction and closed in the other, and vessels carrying dangerous cargo, large vessels and deep draught vessels are not admitted; at half a mile or below, transit traffic closes in both directions. The regulation defines a deep draught vessel as one of 15 m draught or more and a large vessel as one of 200 m length overall or more.

IMO sits alongside both. Assembly Resolution A.827(19) of 23 November 1995 confirmed the adoption of the Rules and Recommendations on Navigation through the Strait of Istanbul, the Strait of Canakkale and the Marmara Sea, and states in terms that they are established purely for safety of navigation and environmental protection and are not intended to affect or prejudice the rights of any ship under international law, including UNCLOS and the 1936 Montreux Convention. Its Annex 2 advises vessels of 15 m draught or more, and vessels over 200 m in length overall, to navigate the Straits in daylight. Turkey is not a party to UNCLOS.

The Turkish state VTS operator gives the waterway as the Istanbul Strait at 17 nautical miles, the Marmara Sea at 110 and the Canakkale Strait at 37, a total of 164 nautical miles between the Black Sea and the Aegean.

Canals under treaty: Constantinople 1888 and the Panama arrangements

A canal is not a strait, and its openness rests on treaty and on the owner’s undertakings rather than on any UNCLOS navigational right.

At Suez the instrument is the Convention respecting the Free Navigation of the Suez Maritime Canal , signed at Constantinople on 29 October 1888. Article I, as published by the Suez Canal Authority itself, provides that the Suez Maritime Canal shall always be free and open, in time of war as in time of peace, to every vessel of commerce or of war, without distinction of flag. The Authority publishes it alongside the Nationalization Decree, Republican Decree Law No. 30 of 1975 and Law No. 4 of 1998.

At Panama the position is routinely misdescribed, including in accounts that are otherwise careful. The United States never held sovereignty over the Canal Zone to transfer. The Panama Canal Treaty of 7 September 1977 recites that the parties acknowledge the Republic of Panama’s sovereignty over its territory, and Article I(2) provides that Panama, as territorial sovereign, grants the United States the rights necessary to regulate transit and to manage, operate, maintain, improve, protect and defend the Canal. Article III(1) repeats the phrase. Article II(2) terminated the Treaty at noon, Panama time, on 31 December 1999. What ended on that date was the grant of operating rights.

The companion Treaty Concerning the Permanent Neutrality and Operation of the Panama Canal, signed the same day and in force from 1 October 1979, has no termination date. It declares the Canal’s neutrality so that it shall remain secure and open to peaceful transit by the vessels of all nations on terms of entire equality, requires under Article III(1)(c) that tolls and other charges for transit and ancillary services be just, reasonable and equitable, and provides in Article V that after the Panama Canal Treaty terminates only Panama shall operate the Canal. The operating body is the Panama Canal Authority, an autonomous public-law entity created by Article 316 of Title XIV of the Political Constitution of Panama, whose Article 315 declares the Canal an inalienable patrimony of the Panamanian Nation open to the peaceful and uninterrupted transit of ships of all nations.

Effective 19 August 2026.

Transit cost: the toll, the tonnage basis and the queue

A canal toll is charged on a tonnage measure of the ship, not on the weight of the cargo it carries, and the two large canals use different measures. That single fact defeats most quick route comparisons, because a figure lifted from one canal cannot be applied to the other.

PC/UMS and SCNT: two bases for one hull

Panama charges on the Panama Canal Universal Measurement System . Under Article 10 of the Panama Canal Authority’s Regulations for the Admeasurement of Vessels, PC/UMS Net Tonnage equals K4(V) plus K5(V), where V is the total volume of enclosed spaces expressed in cubic metres. For vessels charged on displacement, PC/UMS equals 0.56 times the fully loaded displacement in long tons. The regulation states that a TEU represents a volume equal to 1,360 cubic feet.

Suez charges on Suez Canal Net Tonnage , a separate scheme with its own rules descending from the canal’s nineteenth-century measurement regime, evidenced by the Suez Canal Special Tonnage Certificate a ship carries alongside its International Tonnage Certificate.

The practical consequence is procedural rather than arithmetic. A single hull carries one PC/UMS number and a different SCNT number, computed under different rules by different bodies, and neither is the ship’s gross tonnage under the 1969 Tonnage Convention. A clean route comparison measures the ship on each canal’s own basis and applies each canal’s own published rate. Quoting one canal’s tonnage against the other canal’s rate produces a number that is wrong in a way nothing in the calculation will reveal. Anyone building a comparison needs the two certificates, not a conversion factor between them, and tonnage measurement sets out why the schemes diverged.

The Panama toll itself has at least two components. The Panama Canal Authority states that the structure is based on a fixed rate determined according to vessel size category and the set of locks used, plus a rate per vessel capacity, with a maximum amount payable depending on the size category.

At Suez the published base is a tapered scale in Special Drawing Rights per SCNT. Under the schedule applicable from 15 January 2024, a laden crude oil tanker pays 11.04 SDR per SCNT on the first 5,000 tons, then 7.82, 5.91, 2.93, 2.53, 2.17 and 2.13 on the successive bands, with a ballast scale running from 9.40 down to 1.82. Dry bulk carriers start at 10.13 laden and LNG carriers at 10.42.

A surcharge layer sits on top of that base and it is currently large. Suez Canal Authority Periodical No. 16/2026 of 7 June 2026 raised the surcharge on laden crude oil tankers to 37 percent of normal transit dues from 25 percent, and on ballast crude oil tankers to 27 percent from 15 percent. Circular No. 2/2026 of the same date applies 12 percent to containerships, calculated on total transit dues including the surcharges for tiers of containers on the weather deck rather than on normal dues alone, which is a materially different base and is easy to miss. Periodicals 25/2026 and 26/2026 raised special floating units and other vessels to 26 percent from 14 percent. All took effect on 15 July 2026, and the Authority states that the surcharges are temporary and may be amended or cancelled according to market conditions.

Booking, slot rationing and the auction

At Panama the transit itself has to be reserved, and the reservation market is a separate cost from the toll. OP Notice to Shipping N-7-2026 sets a special period for commercial passenger vessels 730 to 366 days ahead, a first period 90 to 15 days ahead for the Panamax locks and 90 to 31 days for the Neopanamax locks, a period 1.a of 30 to 15 days for the Neopanamax locks only, a second period 14 to 8 days ahead and a third period 7 to 2 days ahead closing at 1500. Vessels are categorized as neopanamax, supers at 27.74 m beam or over, and regulars below that beam.

Auctioned slots are allocated to the highest bidder, from a base price in the Official Maritime Tariff, with a minimum bid increment of USD 1,000 and an automatic two-minute extension whenever a higher valid bid arrives in the closing two minutes. The Authority does not issue public price releases: bidding history is published within the auction system to registered participants after closing, and the Authority has stated that auction prices are not set by the waterway but influenced by market dynamics. Individual clearing prices that circulate in the market are press-reported rather than Authority-confirmed, and should be attributed that way.

The drought record shows what slot rationing looks like when it is severe. Advisory to Shipping A-48-2023 of 30 October 2023 records capacity already reduced to approximately 32 vessels per day since 30 July 2023, October precipitation the lowest on record since 1950 at 41 percent below normal, and then a stepped reduction in booking slots: 25 from 3 November 2023, 24 from 7 November, 22 from 1 December, 20 from 1 January 2024, and 18 per day from 1 February 2024 until further notice. The Authority describes 36 daily transits as the figure typically offered during the rainy season. Recovery followed, reaching 33 daily transits from 11 July 2024 and 34 from 22 July 2024, and the Authority’s April 2026 operations summary gives an oceangoing daily transit average of 38.70 with a Canal Waters Time of 32.33 hours.

Waiting time is more modest than the drought headlines suggested. The Authority stated in April 2024 that more than three-quarters of vessels waiting outside the canal held reservations and would transit on a predetermined date with minimal to no waiting, and that the average wait for vessels arriving without reservations that year had been just under 2.5 days, against 3.6 days in the first quarter of 2023 and 3.8 days in the same period of 2022.

Waiting time, the CII, and who pays

Time at anchor is a cost even where no fee is charged, and since 2023 it carries a regulatory penalty as well. The attained annual operational carbon intensity indicator under MEPC.352(78) is computed from the mass of CO2, the ship’s capacity and the total distance travelled in nautical miles. Fuel burned at anchor increases the numerator and adds nothing to the distance, so the rating worsens.

No correction is available for it. MEPC.355(78) permits a voyage adjustment deducting fuel only for scenarios under MARPOL Annex VI regulation 3.1 that may endanger safe navigation and for sailing in ice conditions, and any deducted fuel must have its distance deducted too. The one anchorage relief in the guidelines is tanker-specific, for a ship reporting itself part of a ship-to-ship operation. Canal queuing attracts none of it. The obligation reaches ships of 5,000 gross tonnage and above in the listed categories, under MARPOL Annex VI regulation 28.1 as inserted by MEPC.328(76) and in force from 1 November 2022, with the first calculation after the end of calendar year 2023. The threshold matters for chokepoint planning because it leaves much of the coastal and short-sea fleet outside the penalty entirely. What is CII covers the rating bands and the corrective action plan.

Who bears the dues depends on the charter form, and the flat statement that owners pay under a voyage charter and charterers under a time charter hides that. Under a time charter on NYPE 2015, clause 7(a) names canal dues expressly among the items charterers provide and pay for while the vessel is on hire, an item BIMCO added for the avoidance of doubt after earlier editions left it inside “all other usual expenses”. Under a voyage charter on GENCON 1994 there is no canal dues clause at all: dues fall on owners because clause 13(a) puts all dues, charges and taxes customarily levied on the vessel on owners, and because freight is an all-in figure. Both are default positions and both are routinely varied by rider clause, which is why the voyage charter party and time charter party articles treat the allocation as a drafting question rather than a rule.

The diversion decision

The commercial value of a chokepoint is the distance it saves against the next-best route, and a toll is priced against that saving. When a toll rises, a slot becomes scarce, or the direct route becomes unsafe, an operator compares the higher direct cost against the longer route, and at some break-even the longer route wins.

The standing alternatives

Distances for the Shanghai to Rotterdam pair are from Notteboom, Pallis and Rodrigue and are academic rather than authority figures. Effective 19 August 2026.

The Suez case is the one with published numbers. Shanghai to Rotterdam runs about 10,600 nautical miles and roughly 27 days through Suez against about 13,800 nautical miles and roughly 35 days around the Cape, a difference of some 3,200 nautical miles and about 8 days. UNCTAD measured the fleet-wide effect of the 2024 rerouting instead of a single pair, finding that the Cape detour added approximately 30 percent to voyage lengths and contributed to an estimated 11 percent increase in container TEU-mile demand. The Cape route carries no toll and no draught limit, which is why the largest crude tankers use it by design rather than by necessity.

The Hormuz row is the important one, because it is the only chokepoint in the set with no maritime alternative at all. A few pipelines bypass a fraction of Gulf volume to the Red Sea and the Gulf of Oman, and the rest has no route that does not pass the strait. That absence is what gives Hormuz its weight, and it is why a disruption there cannot be managed by rerouting the way a Suez disruption can.

What a diversion does to the voyage estimate

The break-even is ship-specific and market-specific, and no universal figure exists. What can be stated is the structure: the added bunkers, added charter days and schedule cost of the longer route against the toll plus the queue cost plus any war-risk premium on the direct route. Every term moves. A canal authority raising a toll is bidding against the bunker price, and against a freight market that decides what an extra fortnight of hire is worth. Voyage estimation sets out the full calculation.

One effect runs against intuition and is worth stating plainly. A Cape diversion can improve a ship’s CII rating while increasing its absolute emissions, because the CII is an intensity measure, fuel per capacity-mile, rather than a total. A longer route adds both fuel and distance, and a diversion that also removes weeks of waiting at anchor removes fuel burned against no distance at all. A vessel can therefore emit substantially more CO2 on a Cape routing and still record a better annual rating than it would have queuing for a slot.

Security, war risk and how the charter allocates it

A narrow passage every ship must use is where armed robbery, attack and state pressure concentrate, and the cost of that risk lands on a named party under the charter rather than on the passage. Two things about the current picture cut against the standard account: the risk has moved, and the war-risk clauses that allocate it were rewritten in 2025.

Where the risk actually is

The Malacca Strait is no longer where armed robbery happens, and the Singapore Strait is. The International Maritime Bureau recorded 80 incidents in the Singapore Straits in 2025, against 43 in 2024, 37 in 2023, 38 in 2022 and 35 in 2021, accounting for over 58 percent of all incidents reported globally, with 21 vessels over 100,000 DWT targeted, two of them crude tankers over 300,000 DWT, and guns reported in 27 incidents against 8 the year before. Over the same period the Malacca Straits recorded a single incident. ReCAAP counted 108 incidents in the Straits of Malacca and Singapore in 2025 against 62 in 2024, a rise of 74 percent and the highest in the nineteen years from 2007 to 2025, with about 87 percent falling in the first seven months and a sharp fourth-quarter decline after Indonesian arrests. IMO’s own annual report recorded 122 incidents in the same area against 91 in 2024.

Those three numbers describe the same phenomenon and differ because the registers draw different boxes on the chart and draw on different reporting channels. A risk assessment should name which register it is quoting rather than treat any one figure as the count.

The security arrangements are frequently misattributed. STRAITREP is not a Singapore system: it is a mandatory ship reporting system adopted by IMO Resolution MSC.73(69) on 19 May 1998 under SOLAS regulation V/8-1, in force from 0000 UTC on 1 December 1998, covering the straits between longitudes 100 degrees 40 minutes E and 104 degrees 23 minutes E in nine sectors, and operated jointly by the vessel traffic services of Malaysia, Indonesia and Singapore. Participation is mandatory for vessels of 300 gross tonnage and above, vessels of 50 m or more in length, towing or pushing units meeting either threshold, vessels of any tonnage carrying hazardous cargo, and all passenger vessels fitted with VHF.

The patrol arrangement is the Malacca Straits Patrol, in place since 2006, with three components: the Malacca Straits Sea Patrol launched in 2004, the Eyes-in-the-Sky air patrols launched in 2005, and the Intelligence Exchange Group formed in 2006. Thailand was an observer from 2005 and a full member from 2008, which is why MALSINDO, the early name of the sea-patrol component alone, is a poor label for the arrangement now.

ReCAAP is a different instrument again, and it is not a littoral-state creation. The Regional Cooperation Agreement on Combating Piracy and Armed Robbery against Ships in Asia arose from a Japanese initiative at the Tokyo conference of April 2000, its Information Sharing Centre was established in Singapore on 29 November 2006, and it has 22 Contracting Parties. Indonesia and Malaysia are not among them. Two of the three Malacca littoral states stand outside the agreement most often credited with the strait’s improvement.

War risk listing and the clauses that allocate it

The Joint War Committee , a joint body of the Lloyd’s Market Association and the International Underwriting Association of London, publishes the Hull War, Piracy, Terrorism and Related Perils Listed Areas. Ships entering a listed area may require additional war risk cover. The current circular is JWLA-034, reviewed in July 2026, listing a composite area covering the Persian and Arabian Gulf, the Gulf of Oman, part of the Indian Ocean, the Gulf of Aden and the southern Red Sea north to latitude 25.5 degrees N, excluding Egyptian territorial waters. The southern Red Sea listing was extended to south of 18 degrees N by JWLA-032 of 18 December 2023, which is the insurance market’s marker for the Red Sea crisis. Neither the Malacca nor the Singapore Strait appears on the current list. Rating is negotiated between underwriters and brokers and the Committee plays no part in it, and every circular states that application to individual contracts is a matter for specific negotiation.

The current BIMCO war risks clauses are CONWARTIME 2025 and VOYWAR 2025 , adopted by the Documentary Committee and announced on 9 April 2025, citing the war in Ukraine and attacks on shipping in the Red Sea. BIMCO recommends replacing the 2013 editions, which are now on its list of earlier clauses. A fixture on the printed GENCON 1994 form still carries VOYWAR 1993 unless the clause is replaced, so the edition has to be written into the fixture rather than assumed.

How they allocate the premium is more precise than the usual summary. Charterers reimburse Insurance Costs to owners rather than carrying the premium directly, where Insurance Costs is a defined term covering additional war risks premiums and the costs of any additional kidnap and ransom insurance; the owner’s basic war risk cover stays with the owner. Crew bonuses and additional wages actually paid are separately reimbursable, within 15 days against documentation. The 2025 editions add transparency conditions the older summary hides: owners must, if asked, demonstrate they used reasonable endeavours to obtain appropriate cover and terms including premium, the premium must be shown to have been actually incurred, and any no-claims bonus for the voyage is credited to charterers. Under CONWARTIME 2025 the vessel remains on hire throughout, and the substitute-port nomination window runs to 72 hours. VOYWAR 2025 replaced the old 100-mile freight-adjustment threshold with a calculation on estimated time and extra expenses incurred or saved.

No BIMCO clause exists that is specific to the Red Sea, the Gulf of Aden or a Suez diversion. BIMCO’s response to the disruption was to revise these two clauses and to publish guidance, including a statement in March 2026 that increased risk in the Persian and Arabian Gulf, Gulf of Oman, Indian Ocean, Gulf of Aden and southern Red Sea may not in itself constitute a force majeure event. War risk and high risk areas covers the listing mechanics in full.

What closes a chokepoint

Four things close a chokepoint, and they differ in duration, in whether an engineering fix exists, and in whether anyone can predict the reopening. Sorting a route’s exposure by which of the four it faces is more useful than ranking passages by traffic.

Effective 19 August 2026.

Blockage by a single ship

The Ever Given grounding is the standing example. The ship grounded in the Suez Canal on 23 March 2021, and the Suez Canal Authority announced a successful refloating on 29 March 2021, reporting that push and tow maneuvers had restored 80 percent of the vessel’s direction, with the stern 102 m from the bank against 4 m before refloating. The Authority stated on 31 March 2021 that navigation was back in both directions and the canal was operating at full capacity around the clock. Salvage assets included two Authority dredgers, 15 tugs and nearly 600 workers. The frequently quoted figure of 422 waiting ships and a backlog clearance date of 3 April 2021 circulate as press attributions and do not appear in the Authority’s own contemporaneous statements.

Redundancy decides how bad a grounding is. The Panama Canal’s chambers run in pairs, so one lane can be lost without closing the waterway. The Suez Canal gained a 35 km parallel waterway in 2015, dredged to 24 m and 317 m wide at water level, with 37 km of western by-passes deepened to the same 24 m, and its two-way section now runs 82 km instead of 72 km following the southern sector development the Authority announced complete on 3 February 2025, which widened the channel by 40 m toward the eastern bank from km 132 to km 162, added a new 10 km doubled section from km 122 to km 132, and raised depth there from 66 ft to 72 ft. A single-lane reach with no bypass is the configuration with no redundancy at all, and it is where the Ever Given grounded.

Water: why drought closes a lock canal and not a sea-level cut

Every Panama lockage spends fresh water from Gatun Lake, and a sea-level canal spends none. That difference is the whole of the drought exposure, and it is structural rather than a matter of management.

The 2023 and 2024 sequence is documented above. It has recurred: Advisory to Shipping A-22-2026 of 1 July 2026 set the authorized Neopanamax draft at 14.94 m from 24 July 2026 and 14.78 m from 15 August 2026, and an Authority announcement of 5 August 2026 set 14.63 m from 26 August 2026 and 14.48 m from 3 September 2026. As of 19 August 2026 the authorized Neopanamax draft is 14.78 m, against a published maximum of 15.24 m. The Authority states that these adjustments do not affect the number of daily transits, which distinguishes the 2026 sequence from 2023: this time the canal is throttling how deeply ships load rather than how many transit.

Conflict: the Strait of Hormuz as of 19 August 2026

The Strait of Hormuz is not operating normally, and the two agencies that track it do not describe it in the same words. The International Energy Agency’s Oil Market Report of 12 August 2026 refers to the ongoing closure of the Strait of Hormuz and states that the passage was effectively closed again in early July, after a United States and Iran memorandum of understanding of 17 June 2026 sought to resume traffic. The US Energy Information Administration’s Short-Term Energy Outlook of 11 August 2026 assumes shipments will remain severely constrained through August with flows slowly increasing in September, and does not expect production and trade patterns to return to pre-conflict status until early 2027. Read both against their latest releases before relying on this paragraph.

The measured collapse is the citable fact. The Energy Information Administration recorded 4.9 million barrels per day of crude oil and petroleum liquids through the strait in the second quarter of 2026, against 21.6 million barrels per day in the fourth quarter of 2025. Before the disruption the strait carried about 20.9 million barrels per day in the first half of 2025, which the Administration put at about 20 percent of global petroleum liquids consumption and one quarter of total global maritime traded oil, plus 11.4 billion cubic feet per day of liquefied natural gas, over 20 percent of global LNG trade.

IMO has acted on it. An extraordinary session of the IMO Council on 18 and 19 March 2026 called for the establishment of a safe maritime framework, as a provisional and urgent measure, to facilitate the safe evacuation of merchant ships confined within the Gulf region; an evacuation run from 23 to 26 June 2026 moved 136 vessels and approximately 2,900 seafarers; and the Council at its 137th session on 13 July 2026 adopted a resolution stressing that the right of transit passage through straits used for international navigation should not be threatened, impeded, denied, hampered, impaired or suspended.

A transit fee has appeared where no charging right exists. United States Treasury sanctions guidance issued on 28 April 2026 and updated on 29 May 2026 records that Iran created an entity called the Persian Gulf Strait Authority to collect tolls from and extort vessels transiting the strait, and that payments to it or guarantees from it for safe passage are not authorized for United States persons, United States financial institutions or United States owned or controlled foreign entities. The Persian Gulf Strait Authority was designated on 27 May 2026. So a demand for payment exists in fact while no charging power exists in law, and meeting the demand carries sanctions exposure. Marine insurers have not withdrawn: the Joint War Committee reports that hull war insurance cover remains in place and available in the London market through both Lloyd’s syndicates and IUA companies, while describing the situation as evolving and highly unpredictable, with more than 45 attacks on commercial tonnage and many ships remaining at anchor.

The Red Sea position moved with it. Oil flow through Bab el-Mandeb fell from 9.3 million barrels per day in 2023 to 4.1 million in 2024 and 4.2 million in the first half of 2025, and combined Suez Canal and SUMED pipeline flow fell from 8.8 million to 4.8 million and 4.9 million over the same periods, with LNG through Suez collapsing from 4.1 billion cubic feet per day in 2023 to 0.5 in 2024. Traffic recovered through late 2025 and into early 2026, the Suez Canal Authority reporting on 3 March 2026 that traffic was flowing normally in both directions with 56 vessels that day, while noting that suspension by some major lines remained a temporary measure contingent on the security situation. It then deteriorated again: the Energy Information Administration reported in August 2026 a new blockade threat on Saudi oil exports through Bab el-Mandeb, and the Joint War Committee reports a Houthi embargo of Saudi ports and a northward adjustment of the Red Sea notification line.

Perim divides Bab el-Mandeb into two straits. NGA Sailing Directions describe Large Strait, between the African shore and the island, and Small Strait, between the island and the Arabian shore, and recommend Large Strait because many casualties have occurred in Small Strait. An IMO-adopted traffic separation scheme lies in the strait with a precautionary area at its northern entrance.

Inland waterways under the same logic

Chokepoint logic does not stop at the coast. An inland waterway carries every constraint an ocean chokepoint imposes, scaled to barge convoys: a lock caps convoy dimensions the way a chamber caps a ship, a low-water season caps loaded draught the way a drought caps a canal, and a treaty regime governs access the way a convention governs a strait.

River class, locks and governance

The Danube River basin is the European case. The river runs 2,857 km from the Black Forest to the Black Sea, draining 801,463 km2 across 19 countries. Its largest locks are Iron Gate I at river km 942.90 and Iron Gate II at km 863.70, each with two chambers 310 m long and 34 m wide.

Capacity is graded by waterway class , under the classification the European Conference of Ministers of Transport adopted in 1992 and the AGN agreement carries. The class is determined by the horizontal dimensions of the vessels or pushed units, especially their width. Class VI covers convoys of 22.80 m beam across its a, b and c subdivisions, running from 95 to 110 m length at 3,200 to 6,000 tonnes for VIa up to 270 to 280 m at 9,600 to 18,000 tonnes for VIc. Class VII, the highest, covers convoys of 33.00 to 34.20 m beam and 195 to 285 m length at 14,500 to 27,000 tonnes, with a minimum bridge clearance of 9.10 m. The Danube downstream from Belgrade to the delta is Class VII, navigable by nine-unit convoys; the reaches from Budapest to Belgrade are Class VIc and from Regensburg to Budapest Class VIb.

Two treaties govern, under two bodies, and conflating them is a common error. Navigation runs under the Convention regarding the Regime of Navigation on the Danube, signed at Belgrade on 18 August 1948 and administered by the Danube Commission in Budapest. Water protection runs under the separate Danube River Protection Convention of 1994, administered by the ICPDR in Vienna. The river joins the Rhine system through the Rhine-Main-Danube Canal, 171 km long with 16 locks, completed in 1992.

The river as an alternative when the sea route closes

After the Black Sea deep-sea ports were closed to Ukrainian export in 2022, the European Union’s Solidarity Lanes routed grain through the lower Danube ports of Reni, Izmail and Galati to the sea at Constanta. The pattern matches the Cape standing in for Suez: an alternative exists, it is longer and more expensive, and its capacity is a fraction of what the blocked route carried. The handoff between the inland leg and the deep-sea leg happens at the port, and the modal break is where cost and risk pass between seller and buyer under the applicable Incoterms rule, which freight forwarding and incoterms sets out and ports and terminals overview covers from the terminal side.

Scope of the four deep-dive articles

Each leaf article below takes one passage to depth. This hub carries the comparison; the leaf carries the geometry, the tariff history and the operating detail.

• Panama Canal holds the lock geometry and the expansion history, the full toll structure and booking mechanics, the watershed and its water management, and the transfer of operations in 1999.
• Suez Canal holds the beam against draft envelope in full, the convoy and pilotage regime and its liability position, the SCNT tariff and circular cycle, the 1888 Convention and the 1957 Egyptian Declaration, the 2015 and 2025 channel developments, and the traffic and revenue series.
• Strait of Malacca holds the traffic separation scheme and Deep Water Route, the STRAITREP sectors, the security regime and its history, and the littoral-state cooperative arrangements.
• Danube River basin holds the reach-by-reach waterway classes, the lock inventory, the Belgrade and ICPDR regimes, and the fleet that works the river.

Limitations

This article maps chokepoints and the size classes they set. It is not a transit manual and does not replace the authority’s current notices. Canal dimensions, draught limits, tolls and surcharges change frequently: the Panama Canal Authority issued four draft adjustments in 2026 alone, the Suez Canal Authority revised its surcharges with effect from 15 July 2026, and a published size-class figure is a planning number for a fleet rather than a permission for a named ship on a named day. Before fixing a voyage, confirm the current draught, air draft and beam limits and the live tariff against the Panama Canal Authority and the Suez Canal Authority directly.

Several figures that circulate widely on this subject are not stated here because no primary source could be found for them, and an unverifiable number is worse than an acknowledged gap. Among them: the controlling charted depth of the Strait of Malacca and any Malaccamax draught derived from it, the narrowest navigable width of the Phillip Channel, the annual transit count through the strait, the controlling depths of the Lombok and Sunda alternatives, a per-lockage fresh water volume for either Panama lock set, the Neopanamax lock chamber dimensions, and the Ever Given backlog ship count and clearance date. Figures for those items found elsewhere should be traced to their source before being relied on.

The Strait of Hormuz position stated here is dated 19 August 2026 and describes a situation the sources themselves call evolving and highly unpredictable. The strait was described as closed, then subject to a memorandum of understanding on 17 June 2026, then effectively closed again within about three weeks. Any operational or commercial decision needs the current position from the International Energy Agency, the US Energy Information Administration, UKMTO and the Joint War Committee rather than this article.

The law-of-the-sea account is a summary of the instruments named. Whether transit passage binds a non-party as customary international law is genuinely disputed and is not resolved here, and neither is whether the Turkish national traffic regime is consistent with Article 2 of the Montreux Convention. The rights of transit passage, the enforcement powers of littoral states, and the applicable war-risk and sanctions regime turn on the specific passage, the flag, the ownership and the cargo. A routing decision through a contested strait needs current legal, sanctions and war-risk advice.

Related Articles

• Panama Canal : the lock canal, the Panamax and Neopanamax envelopes, and the PC/UMS toll basis.
• Suez Canal : the sea-level cut, the beam-versus-draught envelope, and Suez Canal Net Tonnage.
• Strait of Malacca : the busiest international strait, the Deep Water Route, and the STRAITREP and patrol regimes.
• Danube River basin : inland navigation, the UNECE waterway classes, and the Belgrade and ICPDR conventions.
• Container ship size classes : how the box fleet settled around the Panama and Suez limits.
• Bulk carrier size classes : the dry fleet’s size ladder and its chokepoint anchors.
• Tanker size classes : where Suezmax and the very large crude carrier sit against the passages.
• Tonnage measurement : why a canal measures a ship on its own basis rather than on gross tonnage.
• Squat effect : why speed reduces the draught a ship can safely transit at.
• Voyage estimation : turning a routing choice into bunkers, days and dues.
• What is CII : the intensity rating that a canal queue worsens and a diversion can improve.
• War risk and high risk areas : listed areas, additional premium, and how a chokepoint becomes one.
• Voyage charter party : why canal dues sit with owners absent a rider clause.
• Time charter party : the NYPE clause that names canal dues as a charterers’ item.
• Freight forwarding and incoterms : where cost and risk pass at the modal break.
• Ports and terminals overview : the place where the inland and deep-sea legs of a route meet.
• Charter parties overview : how canal dues and war risk are allocated between owner and charterer.
• Maritime security and risk : the wider security picture a chokepoint concentrates.