Maritime routing

Realistic sea routing for Panamax, VLCC, and ULCV vessels, reflecting global chokepoints, canal limits, and fallback cape routes for accurate distance calculations.

Maritime routing is one of the cornerstones of international trade. More than 80% of global goods are transported by sea, and understanding how vessels move across the oceans is critical for logistics, planning, and distance calculations.

Unlike roads or airways, sea routes are not unlimited open space: large vessels must navigate through specific passages, straits, and canals that connect oceans and seas. These chokepoints can become bottlenecks due to draft limits, geopolitical risks, congestion, or seasonal ice.

Distance Tools models these maritime passages in order to provide realistic distance calculations for different vessel classes. This ensures that when you compute a route for a container ship or an oil tanker, the distances reflect the actual navigable routes these vessels use in practice.

By modeling real-world maritime constraints, Distance Tools can:

• Produce realistic sea distances for container and tanker routes.

• Adapt to closures and risks (e.g. Suez blocked, Panama drought).

• Support multiple vessel profiles for flexible planning.

• Reflect both global arteries (Suez, Panama, Malacca) and fallback routes (Capes, Lombok, Makassar).

This ensures that when you request maritime distances via the Distance API, the numbers reflect how ships actually sail, not just straight-line great-circle distances.

Vessel classes

Different vessels have different constraints. A small Panamax ship can transit most man-made canals, while the largest oil tankers (VLCC) or container ships (ULCV) are too deep or wide for some passages.

Distance Tools currently models three major vessel classes:

• Panamax → smaller bulk carriers and container ships designed to fit the original Panama Canal.

• VLCC (Very Large Crude Carrier) → huge oil tankers, some of the deepest draft vessels in the world.

• ULCV (Ultra Large Container Vessel) → the largest container ships used on Asia–Europe trade lanes.

Vessel restrictions

Vessel Class	Specifications	Restricted Passages	Forbidden Passages
Panamax	≤80k DWT, ~12m draft	Kiel Canal (draft-limited), Magellan Strait (difficult weather), Torres Strait (shallow)	Bering Strait, Northwest Passage, Northeast Passage, Corinth Canal
VLCC	200–320k DWT, ~20–22m draft	Malacca Strait (Malaccamax limit), Magellan Strait (navigable but impractical)	Suez Canal (too deep fully laden), Panama Canal, Sunda Strait, Kiel Canal, Corinth Canal, Bosphorus & Dardanelles (too narrow), Torres Strait, Arctic routes (NW/NE/Bering)
ULCV	14–24k TEU, ~14–16m draft	Malacca Strait (draft/size limit), Panama Canal (≤14k TEU only), Magellan Strait (navigable but impractical)	Sunda Strait, Kiel Canal, Corinth Canal, Bosphorus & Dardanelles, Torres Strait, Arctic routes (NW/NE/Bering)

Routing profiles

The table below summarizes the major global chokepoints and whether each vessel class can use them.

Passage / Route	Panamax	VLCC	ULCV	Notes
Suez Canal	✅ Allowed	❌ Forbidden	✅ Allowed	Core Asia–Europe artery; VLCC must lighter
Panama Canal	✅ Allowed (old locks)	❌ Forbidden	⚠️ Restricted (≤14k TEU, Neopanamax)	Drought can restrict further
Malacca Strait	✅ Allowed	⚠️ Restricted (Malaccamax ~200k DWT)	⚠️ Restricted (ULCV near draft limits)	Heavy congestion
Sunda Strait	✅ Allowed (regional)	❌ Forbidden	❌ Forbidden	Too shallow/narrow for VLCC/ULCV
Gibraltar Strait	✅ Allowed	✅ Allowed	✅ Allowed	Deep water, universal
Dover Strait	✅ Allowed	✅ Allowed	✅ Allowed	Dense TSS but usable
Bering Strait	❌ Forbidden	❌ Forbidden	❌ Forbidden	Arctic only, no commerce
Magellan Strait	⚠️ Restricted	⚠️ Restricted	⚠️ Restricted	Navigable but impractical; Cape Horn preferred
Bab el-Mandeb Strait	✅ Allowed	✅ Allowed	✅ Allowed	Strategic; conflict/piracy risks
Kiel Canal	⚠️ Restricted (draft-limited)	❌ Forbidden	❌ Forbidden	Max draft ~9.5m
Corinth Canal	❌ Forbidden	❌ Forbidden	❌ Forbidden	Very small ships only
Northwest Passage	❌ Forbidden	❌ Forbidden	❌ Forbidden	Not commercially viable
Northeast Passage	❌ Forbidden	❌ Forbidden	❌ Forbidden	Not commercially viable
Bosphorus Strait	✅ Allowed (small Panamax)	❌ Forbidden	❌ Forbidden	Narrow, pilotage; Black Sea access only
Dardanelles Strait	✅ Allowed (small Panamax)	❌ Forbidden	❌ Forbidden	Companion to Bosphorus
Strait of Hormuz	✅ Allowed	✅ Allowed	✅ Allowed	Vital for oil, geopolitical risk
Lombok Strait	✅ Allowed	✅ Allowed	✅ Allowed	Deep alternative to Malacca
Makassar Strait	✅ Allowed	✅ Allowed	✅ Allowed	Used with Lombok for bypass
Torres Strait	⚠️ Restricted (draft-limited)	❌ Forbidden	❌ Forbidden	Very shallow, regional trades
Cape of Good Hope	✅ Allowed	✅ Allowed	✅ Allowed	Fallback route for Suez closures
Cape Horn	✅ Allowed	✅ Allowed	✅ Allowed	Harsh conditions, fallback for Panama oversize

When using the default profile, Distance Tools applies no restrictions — all passages are treated as open, regardless of vessel size.

Open-Source Routing Engine

GitHub - StephanGeorg/searoutes: Fast, flexible maritime routing for global trade lanes — profiles, snapping, configurable rules, and antimeridian support.GitHub

Maritime routing in Distance Tools is powered by the open-source library searoutes. This library builds realistic sea networks from authoritative datasets and applies the vessel class restrictions shown above. By relying on open data and open technology, we ensure transparency in how routes are calculated and give developers confidence in both the methods and results.