# Maritime routing

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**](#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](#routing-profiled)) or container ships ([ULCV](#routing-profiled)) 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**](https://en.wikipedia.org/wiki/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](https://en.wikipedia.org/wiki/Traffic_separation_scheme) 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                                  |

{% hint style="success" %}
When using the **default** *profile*, Distance Tools applies **no restrictions** — all passages are treated as open, regardless of vessel size.
{% endhint %}

### Open-Source Routing Engine

{% embed url="<https://github.com/StephanGeorg/searoutes>" %}

Maritime routing in **Distance Tools** is powered by the open-source library [**searoutes**](https://github.com/StephanGeorg/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.


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