AIS and Collision Avoidance

On an offshore regatta, you share the water not only with competitors but also with container ships, ferries, fishing vessels, and tankers. At night, in fog, or in heavy seas, visual perception alone is not enough. The Automatic Identification System (AIS) has revolutionized maritime traffic safety – yet AIS is not an automatic solution for collision avoidance. It provides data that an attentive crew must interpret correctly and translate into decisions. Those who understand AIS, radar, navigation lights, and the COLREGS (International Regulations for Preventing Collisions at Sea) as an integrated system navigate not only more safely but also preserve valuable focus for tactics and routing.

What is AIS and why is it relevant for regattas?

AIS is an automatic identification and tracking system for vessels. Position, course, speed, and identification data are exchanged at short intervals via VHF radio. Onboard receivers – plotters, laptops, or dedicated AIS devices – display other vessels as symbols on the chart and provide numerical data such as CPA (Closest Point of Approach) and TCPA (Time to CPA).

For regatta sailors, AIS is particularly important because:

• Visibility is limited – during night and offshore navigation, landmarks are missing; ship lights are hard to assess from a great distance.
• Speeds are high – a 300-meter freighter travels at 18–22 knots; when approaching from astern, there is little reaction time.
• Regatta courses cross shipping lanes – Fastnet, Middle Sea Race, and Transat routes pass through heavily trafficked shipping routes.
• Crew fatigue – a structured watch system must define AIS watch as a fixed duty.

AIS classes and onboard transponders

There are two main classes of vessel AIS:

Recommendations for regatta yachts

1. Install an AIS transponder – For offshore regattas, a Class B or Class B+ transponder is often required or strongly recommended in the sailing instructions.
2. Enter MMSI correctly – The Maritime Mobile Service Identity uniquely identifies the boat; errors lead to false alerts for the coast guard.
3. Maintain boat name and callsign – Other vessels and VTS (Vessel Traffic Service) can then address you directly.
4. Mount antenna high and clear – Masthead or spreader; metal deck structures and low mounting drastically reduce range.
5. Check receiver separately – A receive-only AIS receiver makes you invisible to traffic – insufficient for offshore.

Using CPA, TCPA, and alarms correctly

The most important AIS metrics for collision avoidance:

• CPA (Closest Point of Approach) – The smallest distance two courses are expected to reach. A CPA under two nautical miles with a freighter is critical.
• TCPA (Time to CPA) – Time until the closest approach. Under 20 minutes with a fast motor vessel requires immediate action.
• Bearing and relative motion – A stable bearing over several minutes means: collision course. A changing bearing indicates an avoiding course.

AIS collision assessment – procedure

Typical alarm thresholds

COLREGS and AIS: rules vs. technology

AIS does not change the basic rules and right-of-way in regatta traffic – on the contrary: outside the regatta course, the COLREGS apply without restriction. Sailing yachts are often the "give-way vessel" relative to motorized vessels in fairways.

Important COLREGS rules for collision avoidance

1. Rule 5 – Look-out – At all times a proper lookout by sight, hearing, and all available means – including AIS and radar.
2. Rule 7 – Risk of collision – Stable bearing = danger; AIS bearing confirms visual assessment.
3. Rule 8 – Action to avoid collision – Give way early, clearly, and generously; good seamanship.
4. Rule 9 – Narrow channels – Small vessels must not impede the passage of larger vessels.
5. Rule 19 – Restricted visibility – In fog or at night: reduced speed, radar if available, navigation lights set correctly.

Sail vs. motor vessel – who gives way?

• Sail against motor (open sea) – Sail generally has right of way, except when the motor vessel cannot give way (channel, close-hauled).
• Two sailboats – Wind from port has right of way; overtaking from leeward to windward.
• Regatta vs. merchant vessel – Merchant vessels practically always have priority; regatta tactics do not count.

Responsibility in collision avoidance

Combining AIS, radar, and plotter

AIS and radar complement each other. AIS provides identity and course data; radar also shows non-AIS targets (wooden boats, debris, some fishing vessels). An integrated GPS plotter with AIS and radar overlay is standard on modern offshore yachts.

Strengths and limitations compared

Electronic collision avoidance – workflow

Watch protocols and crew roles

Collision avoidance rarely fails due to missing technology, but due to lack of attention. A clear watch protocol is mandatory.

AIS watch during the night watch

• Dedicated plotter monitor – One display stays on AIS/radar chart; no switching to GRIB or entertainment.
• Set alarm limits in advance – Define CPA/TCPA thresholds in the briefing, do not improvise.
• Logbook entries – Document every large vessel within 5 nm with time, bearing, and action taken.
• Radio ready – VHF on channel 16, handheld radio for the lookout on deck.
• Handover at watch change – Approaching vessels and open situations handed over verbally.

Checklist: AIS before offshore start

• Transponder transmitting (green TX status on device)
• MMSI, boat name, and callsign correct
• Antenna and cable checked
• CPA/TCPA alarms configured
• Plotter shows AIS symbols (test with harbor vessel)
• Radar calibrated and ARPA active
• Navigation lights functional per COLREGS
• VHF channel 16, DSC distress call tested
• Watch rotation with AIS responsibility in briefing
• Paper chart as backup in cockpit

Checklist: collision avoidance underway

• Permanent visual lookout
• AIS alarms active and monitored
• Radar rotation in restricted visibility
• Navigation lights set correctly
• Speed reduced in restricted visibility
• Radio contact when uncertain (security call)
• Course change documented
• Logbook entries for large vessels
• Crew informed of approaches
• When in doubt, give way early

Practical scenarios on regatta courses

Choke point: Dover Strait or Gibraltar

In heavily trafficked straits, regatta courses cross international shipping routes. Sailboats must know traffic separation schemes (TSS) and cross them – not sail along them – whenever possible. AIS shows traffic flow; stay early on the leeward side of the TSS, do not enter inbound/outbound corridors.

Approach from astern at night

A container ship from astern is particularly dangerous because it remains invisible for a long time. AIS detects the target early – TCPA provides time to give way. Actions:

1. Change course clearly – At least 30–60 degrees so the course change is visible on radar.
2. Check navigation lights – Sailing yachts need the correct combination (masthead + stern).
3. Security call on VHF – "Motor vessel bearing XXX, this is sailing yacht [Name], CPA less than one mile, altering course to starboard."
4. Do not wait for the large vessel's horn – React proactively.

Regatta fleet and AIS overload

At mass starts like the Barcolana, the plotter shows hundreds of Class B targets. Set filters: only targets under 10 nm, CPA alarms only, or filter by speed (under 5 kn = sailing competition). Regatta competitors collide under the Racing Rules – AIS helps, but racing rules still apply.

Mistakes regatta sailors must avoid

1. AIS as sole source – Without visual lookout and radar, redundancy is missing.
2. Giving way too late – Large vessels do not brake; an avoiding maneuver must be early and generous.
3. Wrong MMSI or silent transponder – Check transponder status after power outage.
4. Alarm fatigue – CPA limits set too tight lead to constant alarms; crew then ignores real dangers.
5. Radio reluctance – A brief security call is better than a close pass.
6. GRIB instead of AIS – Weather routing on the plotter must not displace the traffic chart.

Integration into navigation planning

AIS and collision avoidance belong in the overall planning of night and offshore navigation. Before the start:

• Mark traffic zones on chart and plotter
• Plan TSS and recommended crossing angles
• Reconcile GRIB routing with traffic lanes – the fastest course is not always the safest
• Define emergency harbors and diversion points
• Assign crew roles for AIS, radar, and radio in the watch plan

Typical night watch with AIS

Conclusion

AIS and collision avoidance are inseparable in modern regatta sailing. The system provides precise data on position, course, and approach – but only a disciplined crew that knows the COLREGS, combines radar and visual lookout, and gives way early turns that into safety. Invest in a reliable transponder, train CPA/TCPA alarms as a team, and build AIS watch firmly into every night watch. That keeps your mind free for what you sail for: fast, safe, and successful regattas on the open sea.

Related topics

• Night and Offshore Navigation
• GPS, Plotter, and Classic Navigation
• Night Sailing and Watch System
• Offshore and Long-Distance Regattas
• Basic Rules and Right-of-Way

Last updated: July 4, 2026