Boating Coach US
Aids to navigationQuestion 258 of 352

What light rhythm does a preferred channel mark show?

  1. Only fixed light
  2. Morse A
  3. Groups of two flashes then one flash
  4. Groups of two flashes only
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Correct answer: Groups of two flashes then one flash

The composite group flashing rhythm (two flashes, then one) shows a channel split.

Source: US Code of Federal Regulations (eCFR), 33 CFR Part 62: United States Aids to Navigation System, § 62.45 Light characteristics

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Questions last reviewed: 18 October 2026