Decision Simulator

Tricolor / Kariba / Clary — Two Threats, One Blind Turn

Kariba
Container ship, 580ft, Bahamian-flagged · Dover Strait TSS, Pas-de-Calais, ~20nm NW of Dunkirk · 14 December 2002
Source: BEAmer investigation (French)

5Decision Points 4Possible Outcomes —Avg. Play Time

The Situation

You are the OOW on Kariba, a 580ft container ship, westbound through the Dover Strait Traffic Separation Scheme at night in fog, making 16 knots on a course of 290°T. Two other vessels are in play: Tricolor, a car carrier, is roughly 0.5 miles on your starboard quarter, overtaking you at 17.9 knots. Clary, a bulker, is approaching from the south on a near-90-degree crossing course at 13 knots. Radar shows full course, speed and CPA data for both. In the last fifteen minutes, nobody aboard any of the three vessels has sounded a fog signal or made VHF contact with either of the others.

The Lesson

A vessel that's overtaking you doesn't stop being a collision risk just because your attention has moved to a second, more demanding contact. Before altering course to solve one problem, re-confirm the position of every other vessel your turn will affect — and in genuine multi-vessel risk, VHF/sound-signal contact beats silently guessing what the other bridge team is about to do.

Human Element

This wasn't a failure of radar or technology — every vessel had full course, speed and CPA data on all the others. It was a failure of communication and of tracking two simultaneous threats at once. Kariba's bridge team fixated on Clary, the vessel it expected to give way, and lost track of exactly where the overtaking vessel — Tricolor — actually was the moment it altered course to solve the Clary problem. Two real risks, and the decision that addressed one blindsided the other.

Try the First Decision

Tricolor is overtaking on your starboard quarter, roughly 0.5nm, at 17.9 knots — faster than you're making. Nothing has been said between the two bridges yet.

A. Make VHF/sound contact with Tricolor now to confirm her intentions.
B. She's committed to the overtake — no need to contact her, just keep an eye on the radar.

This is a preview — the full scenario branches from here based on what you choose, with real consequences and a debrief at the end.

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