Responsibilities Between Vessels

The "pickle pyramid"

Memorise this hierarchy. The vessel higher on the list is the stand-on vessel — others must keep out of her way. From most-protected to least:

1. Vessel Not Under Command (NUC) — through some exceptional circumstance, unable to manoeuvre as required by the rules. Two red all-round lights vertically; two black balls by day.
2. Vessel Restricted in Ability to Manoeuvre (RAM) — by the nature of her work (cable-laying, dredging, towing operation, mine clearance, replenishment). Red-white-red vertical lights; ball-diamond-ball shapes.
3. Vessel Constrained by her Draught (CBD) — power-driven vessel which, because of draught and depth/width of navigable water, is severely restricted. Three red all-round lights vertically; black cylinder by day. (Optional indication; not all such vessels claim it.)
4. Vessel Engaged in Fishing — fishing with nets, lines, or trawls that restrict manoeuvrability. Red-over-white all-round (other than trawling); green-over-white (trawling).
5. Sailing Vessel — propelled by sail alone (engine off and out of gear).
6. Power-Driven Vessel — yields to all of the above.

A sailing vessel running her engine is a power-driven vessel for COLREG purposes — even with sails up — and shows the masthead light at night. Forgetting this is one of the most common mistakes in oral exams.

How AIS makes this rule actionable

Rule 18 only works if you can identify the other vessel's status. AIS makes this immediate: navigation status is broadcast in every Class A position report. Your simulator decodes it on every target:

• 0 Under way using engine — power-driven (lowest priority)
• 1 At anchor — Rule 30 lights apply
• 2 Not under command — top of the hierarchy
• 3 Restricted manoeuvrability (RAM)
• 4 Constrained by draught (CBD)
• 7 Engaged in fishing
• 8 Under way sailing — outranks power-driven only

Many commercial OOWs ignore navigation status because they're trained on the lights. The simulator forces you to read both — AIS and visual — and resolve any conflict (a fishing trawler whose AIS still says "under way using engine" is not uncommon at sea).

The simulator scenarios

• Power-vs-sailing — your motor cruiser approaches a sailing yacht on a crossing course. Free demo. Beware: is her engine running? Watch for the masthead light at night.
• Sail-vs-fishing — your sailing yacht approaches a trawler with nets streaming. Fishing wins; you give way (Rule 18(a)(iii)).
• NUC-encounter — a vessel ahead displays two red all-round lights — engine breakdown, drifting. You and every other vessel keep clear.
• RAM-tug-and-tow — RAM lights, towing barge 300 m astern. Plan a passage that clears both the tug and the tow line.
• Fishing-pair — two trawlers working in tandem, both showing fishing lights. Pass between or around — practical decision.

Common mistakes

• Treating a motor-sailing yacht as a sailing vessel — engine on = power-driven, regardless of sail trim.
• Trusting AIS over lights when they conflict — lights are the legal indicator (Rule 18 hierarchy is set by what the vessel is, evidenced by lights/shapes). AIS is supplementary.
• Misreading red-white-red (RAM) as red-over-white (fishing) — always count the lights vertically, not just colour.
• Assuming CBD always shown — CBD is optional indication. Many large vessels constrained by draught simply behave as CBD without claiming it.
• Ignoring the "in sight" qualifier — Rule 18 applies between vessels in sight. In restricted visibility, Rule 19 takes over (different logic).