Lesson previewClassify the Control Before Moving1 section shown
Preview lesson
Classify the Control Before Moving
What you will learn
Distinguish physical access from formal permission at a lock, bridge, weir or narrow opening, then identify the control that governs movement.
An opening that looks usable is not necessarily open to traffic. Read the control first, then prove that the vessel and complete passage fit.
CEVNI separates what a structure appears to be doing from what traffic may do. Red, red and green together, a closed board or the absence of an entry signal can still prohibit entry when gates are moving or an opening is visible. Green or a permissive mark authorises movement only within its stated direction and conditions.
At a bridge or weir, Annex 7 signs identify prohibited, recommended or direction-limited openings. At a lock, entry and exit lights, staff orders and the allotted radio channel control the sequence. National rules, local notices and competent-authority instructions may add or vary requirements.
Use a repeatable decision: observe the exact light or board; translate its formal meaning; check direction, dimensions, traffic and local conditions; choose a reversible action; name the point beyond which you will not proceed without permission. Physical openness never replaces that chain.
Controlled passage decision reader
Compare the observed control, exact meaning, next action and stop boundary before committing.
Schematic plan · read the written state
Observed control
A red and green lock-entry light are shown together while the gates are being prepared.
Exact meaning
Entry remains prohibited. The combined state means prepare to get under way, not enter now.
Next safe action
Hold short, listen on the allotted lock channel when equipped, prepare the boat and wait for green or an express staff order.
Stop boundary
Visible gate movement, a vessel ahead moving or your arrival order does not replace the entry signal.
Read the observed control, its exact meaning, the next safe action and the stop boundary before committing.
Worked example
The lock gates begin to open while red and green entry lights show together.
- 1Name the state: red and green means preparing, not permitted.
- 2Hold before the entry limit, monitor the allotted channel when equipped and ready the vessel.
- 3Enter only after green or an express staff order, then recheck departing traffic and the chamber route.
Sense check: If the decision depends on gate movement rather than displayed permission, the control has been read incorrectly.
| Observation | Formal meaning | Immediate action |
|---|---|---|
| Red | Entry prohibited | Hold before B.5 or the directed limit |
| Red and green | Entry still prohibited; preparing | Prepare and wait for green or an express order |
| Green | Entry permitted | Recheck traffic, dimensions and instruction |
| No lock entry signal | Entry prohibited unless staff expressly order it | Do not infer permission from an open gate |
Use a four-line controlled-passage brief
A crew member can see the structure but has not interpreted its controls.
1. Observe
State the exact light, board, direction and staff or radio instruction.
2. Translate
Say permitted, prohibited, preparing, recommended or reduced-height—not merely open.
3. Verify
Check air draught, width, traffic, current level and the whole route.
4. Boundary
Name where the vessel will hold if permission or clearance is uncertain.
Sense check: A complete brief separates permission from clearance and names a stop point.
Common mistake or limitation
- Following another vessel or visible gate movement through a prohibited signal.
- Calling red and green permission instead of a preparation state.
- Treating a permissive signal as proof of headroom, width or clear traffic.
Recap
- Observe, translate, verify and name the stop boundary.
- Wait on any prohibited or ambiguous state.
- Staff, signals, local rules and actual dimensions must agree.
Optional quick check
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