Ship Collision

Ship collision explained: how risk builds, what COLREGs require, and where the watch misses it

Key takeaways

• A ship collision is an impact between two vessels underway. A vessel striking a bridge, a pier, or a ship at anchor is technically an allision. The NTSB titled its Baltimore investigation a contact.
• COLREGs Rule 7 sets the test. If there is any doubt whether risk of collision exists, it is deemed to exist. That is a deliberately low bar for taking action.
• Lookout failure is the recurring finding. The MAIB found two thirds of vessels involved in collisions were not keeping a proper lookout, and in July 2025 its Chief Inspector wrote that the role of human watchkeepers needs a radical rethink.
• Orca AI adds an independent detection layer to the bridge for ship collision avoidance. SeaPod tracks AIS and non-AIS targets on day and thermal cameras and surfaces CPA and TCPA earlier in the encounter, alongside Radar and ECDIS.

What is a ship collision?

A ship collision is an impact between two vessels that are both underway. In casualty statistics and in insurance, collision is one of the navigational casualty types, alongside grounding, contact and foundering. Collisions are also the event type most associated with fatalities and injuries at sea.

Preventing them is governed by the Convention on the International Regulations for Preventing Collisions at Sea, 1972, adopted on 20 October 1972 and in force since 15 July 1977. COLREGs run to 41 rules across six parts, and they apply to every vessel on the high seas and connected navigable waters.

Most of what determines whether a collision happens is decided long before the two vessels get close, in how well each bridge team builds and holds its picture of the traffic. That is the work of situational awareness.

Ship collision or allision: what about a ship collision with a bridge?

A ship collision involves two moving vessels. An allision is a moving vessel striking a stationary object: a bridge, a wharf, a pier, or a vessel at anchor or moored.

The distinction carries legal weight. In US admiralty, the Oregon rule presumes the moving vessel is at fault in an allision, on the reasoning that a properly navigated vessel should be able to avoid something that isn’t moving. In a collision, fault is apportioned on the facts and on each vessel’s compliance with the navigation rules, and it is frequently shared.

The Baltimore case is the useful reference. When the containership Dali lost electrical power, propulsion and steering on 26 March 2024 and struck the Francis Scott Key Bridge, killing six highway workers, the NTSB titled its investigation “Contact of Containership Dali with Francis Scott Key Bridge and Subsequent Bridge Collapse.” It reached for a third word: contact.

The NTSB adopted its final report on 18 November 2025 and issued it as MIR-25-40 on 10 December. Probable cause was a loose signal wire connection to a terminal block, the result of improper installation of wire-label banding, which caused the loss of electrical power.

So a ship collision with a bridge is, strictly, an allision or a contact. The mechanism is different too: the Dali case turned on electrical failure in the engine room, not on anything the bridge team saw or missed.

What do COLREGs require when risk of collision exists?

Five rules carry most of the weight in a developing encounter.

Rule 5 is worth quoting in full, because it is short and it is the rule most often broken:

“Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.”

The phrase “all available means” is doing real work. It brings Radar, AIS, ARPA and any other detection capability on board into the scope of the rule.

Rule 7 then sets the threshold. Risk of collision shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change, and it may exist even when a bearing change is evident, particularly when approaching a very large vessel or a tow, or when approaching at close range. Assumptions “shall not be made on the basis of scanty information, especially scanty radar information.”

How do shipping collisions develop?

Almost always as a chain, and almost always with time to spare at the start.

1. Detection. One vessel appears on Radar, on AIS, visually, or on none of the three. Small craft, fishing vessels and unlit objects frequently carry no AIS, which is why detection cannot rest on AIS alone.
2. Appraisal. The bridge team works out whether risk exists, using bearing change, CPA and TCPA. This is the step Rule 7 governs, and the step where scanty information does the most damage.
3. Decision. The applicable rule is identified and a maneuver chosen. Rule 8 asks for it to be positive and made in ample time.
4. Action. The maneuver is executed and its effect is checked until the other vessel is finally past and clear.

Break any link and the chain runs to its end. Most casualty reports find the break at step 1 or step 2, well before anyone had to make a difficult decision under pressure.

Where do collisions of ships concentrate?

Allianz Commercial’s Safety and Shipping Review 2026, published in June 2026 and covering calendar 2025, recorded 2,818 reported casualties and incidents on vessels over 100 GT, down 16% on 2024. Vessel collision was the second most common cause at 260 incidents, behind machinery damage and failure at 1,505 and ahead of fire and explosion at 218.

Two regions dominate incident volume: the East Mediterranean and Black Sea with 622, and the British Isles with 619. Between them they account for 1,241 of the 2,818 reported casualties. Those are incident counts across all causes, not collision density, so they describe where shipping activity and reporting concentrate rather than where collision risk is highest per mile.

The EMSA Annual Overview of Marine Casualties and Incidents 2025, covering 2015 to 2024, recorded 26,751 occurrences over the decade. Collision was the primary cause of fatalities in occurrences with ships in 2024, and the predominant event causing injuries across the full ten years.

Traffic separation schemes are the main structural control. The 1972 Convention formally recognized them in Rule 10, and in the Dover Strait the Channel Navigation Information Service, operated jointly by the UK and France from MRCC Dover and CROSS Gris Nez, provides 24-hour Radar surveillance of the traffic. A TSS reduces the number of crossing situations. It does not remove them, and two of the three casualties below happened in or beside one.

What do recent collision investigations show?

The Scot Carrier report, MAIB 5/2023, is the most complete account. The second officer had consumed alcohol before taking the watch and spent much of it on a personal tablet computer, at one point turning on the bridge interior lights and using the searchlight to show his surroundings to a stranger on a video chat site. AIS registered Karin Høj as a dangerous target at 0303 with a CPA of 0.88nm and a TCPA of just under 20 minutes. No audible alert was recorded, because the navigation officers routinely disabled the ECDIS look-ahead, Radar and AIS alarms. They caused too much distraction.

The MAIB’s systemic conclusion is the part worth carrying forward: the tablet “was just the last of many safety barriers to be routinely disabled or negated on Scot Carrier, none of which had been detected during audits.” We wrote about this case in more detail in our post on the night-time collision in the Danish straits.

The underlying pattern is old. The MAIB’s Bridge Watchkeeping Safety Study found that two thirds of all vessels involved in collisions in its cohort were not keeping a proper lookout.

What changed is the MAIB’s view of the remedy. In the introduction to its Annual Report 2024, published July 2025, Chief Inspector Captain Andrew Moll wrote that recent casualties “indicate a need to radically rethink the role of human watchkeepers in the digital age. Humans do not make good monitors and if under-stimulated they will find other things to occupy themselves.”

He immediately added the harder half: as the joint DMAIB and MAIB study on ECDIS usability showed, crews can also be reluctant to use the system functions that would alert them to impending problems. Adding alerts to a bridge that is already saturated with them makes the situation worse, which is why alarm overload is a safety question in its own right.

Are container ship collisions and cruise ship collisions different?

The rules are the same. The consequences scale with the hull.

• Container ship collisions involve large windage areas, long stopping distances and, in the Dali case, enough momentum to bring down a bridge span. Verity was struck by a bulk carrier; Solong was a containership. Size compresses the time available between recognizing risk and running out of options.
• Cruise ship collisions put thousands of people aboard a single hull, so evacuation and passenger management dominate the consequence side even where the navigational error is ordinary.
• Small craft and fishing vessels are a detection problem first. They are frequently unlit, frequently without AIS, and the merchant vessel involved is often unaware anything happened. We looked at that specific gap in our post on fishing boat collisions.

How Orca AI supports collision avoidance

Orca AI adds an observation-based reference layer to the bridge. Radar, AIS, ECDIS and the officer of the watch all stay exactly where they are. The master remains in command.

• Detection that doesn’t depend on AIS. SeaPod combines day and thermal cameras with mandatory ship sensors, including AIS, Radar, GPS, gyro, depth and wind. It detects, tracks and classifies targets that carry no AIS transponder, which is the category Rule 5’s “all available means” is hardest to satisfy for.
• Earlier risk indicators. SeaPod derives CPA, TCPA, COG and SOG and surfaces developing close encounters while the encounter is still a Rule 8 problem, when action can still be positive and made in ample time.

• Alerts that stay usable. Prioritized, verified alerts are the answer to the disabling problem the MAIB documented. An alert an officer trusts is an alert they leave switched on.
• Fleet-level review. FleetView records navigational events continuously, so safety teams ashore can see how close encounters were handled and feed that back into training.
• Awareness beyond the horizon. Co-Captain shares verified, anonymized route hazards and congestion intelligence between Orca-equipped vessels and shore. It is advisory. It does not take control.

A posted lookout is still the rule. What the platform adds is margin on the nights when one isn’t there, and evidence for shore teams about how their fleet navigates. Across the 139 vessels in our NorthStandard cohort, 139 ship-years and more than 10.8 million nautical miles, high-severity close encounters fell 52% over each ship’s first 12 months of AI-assisted watchkeeping.

For more, read our take on the future of collision avoidance from COLREGs to AI, the role of advanced ship collision avoidance systems, the maritime safety glossary entry, and our safety report with NorthStandard.