You’re approaching a lock, the gates are still closed, and a light signal is flashing in a color combination you can’t immediately place. For many newcomers, the first lock passage with their own boat is one of the more unsettling moments on inland waterways. In reality, a lock transit follows a clear, consistent procedure every time. This article walks you through it step by step: how to read the signals, how to behave, and what matters inside the chamber.
How a Lock Works
A lock (Schleuse in German) equalizes the height difference between two water levels, for example where a river drops in elevation or where a canal and a lake sit at different heights. The core element is the lock chamber, an enclosed basin between two gates. If you’re traveling upstream, the water level inside the chamber starts lower; during the locking process, water is let in until it matches the upper waterway, and only then does the upper gate open. Going downstream works the other way around: water is drained until the chamber matches the lower level.
As a skipper, the technical process happening in the background matters less than behaving correctly before, during, and after the transit, since that’s what actually determines a safe and smooth passage.
Reading the Lock Signals Correctly
Light signals at every lock govern when entry and exit are allowed. The system is standardized nationwide under the Binnenschifffahrtsstraßen-Ordnung, the German inland waterways regulation (you may already know similarly regulated signals from movable bridges, more on that in our article on bridge clearance heights):
- One or two red lights: Entry forbidden. Keep your distance and wait.
- Red and green shown together: The lock is being prepared, but entry isn’t cleared yet. Get ready, but don’t move in.
- One or two green lights: Entry allowed.
Leaving the chamber follows the same basic logic in a simpler form: a red light means the gates aren’t fully open or secured yet and you need to wait, a green light clears you to exit. Never enter or exit on red, even if a gate already looks open enough. The signal accounts for things that aren’t always visible from the outside, such as currents around the gates or an equalization process that hasn’t fully finished.
Approaching and Waiting Before the Lock
Always approach a lock at reduced speed, even before any signal is visible. In the approach area, only moderate speed is allowed, overtaking and pushing ahead are prohibited, unless the lock personnel direct a different order or smaller boats are let through first by mutual agreement.
One point many recreational boaters underestimate: commercial vessels generally have priority in lock areas, regardless of the size of the boats involved. In practice, that often means recreational boats have to wait until cargo vessels have entered and moored, and that they themselves enter the chamber last. Use the waiting time to prepare your boat: rig fenders on both sides, keep lines ready at the bow and stern, and if the lock has one, contact the lock keeper by radio or lock telephone if that’s how the specific lock is set up.
Many larger locks mark designated waiting positions where you should hold before entering. Stick to these markings, and to areas where waiting is explicitly prohibited, for example because the current toward the lock is too strong there.
Entering the Lock Chamber
When you enter on green, keep your speed moderate and steer calmly toward the position assigned by the lock personnel or an obvious open spot. In larger chambers, several recreational boats may lock through together, with or without commercial vessels, so keeping your distance and not getting in anyone’s way matters even more. Always follow the lock personnel’s instructions, even if they differ from where you originally planned to go.
Once you’ve reached your position, moor up, covered in detail in the next section. As a rule, don’t leave the boat while inside the chamber, except when necessary to contact the lock personnel, for instance at a lock telephone confirming you’re ready.
Behavior Inside the Chamber
Inside the chamber, the water level changes by sometimes considerable amounts during the locking process, and your boat needs to move with it safely. That’s why the most important rule for lines in a lock is this: never make a line fast around a bollard, holding cross, ring, or ladder. The line has to run freely and be paid out or taken in by hand, otherwise your boat risks snagging on the chamber wall as the water rises or falls, which in the worst case can capsize the boat or pull it underwater.
Hold the lines loosely throughout the entire transit and keep adjusting them continuously, since incoming or outgoing water can create noticeable currents and turbulence inside the chamber for short periods. Make sure your boat doesn’t collide with the chamber wall, the gates, protective fittings, or neighboring boats; well-placed fenders on both sides of your hull help here (you’ll find more on fender placement and handling lines in our article on docking and undocking).
Switch off the engine as soon as you’ve moored, and only restart it once the exit is cleared by the green signal. This cuts down on exhaust fumes in the enclosed chamber and keeps prop wash from disturbing neighboring boats or their lines. Smoking is off-limits inside the chamber for safety reasons too.
Leaving the Lock
Once the water level has fully equalized, the gates open and the exit signal switches to green. Only now should you fully release the lines, start the engine, and leave the chamber at moderate speed. Here too, the lock personnel may set the order in which boats leave, especially when commercial vessels are involved. Wait your turn instead of pushing ahead, and only pick up speed once you have enough clearance from the lock and other vessels.
Self-Service Locks
On many smaller inland waterways, for example in the Mecklenburg Lake District or the Spreewald, locks aren’t staffed around the clock and are instead set up as self-service locks (Selbstbedienungsschleusen). The overall procedure stays similar, but you take on the role the lock personnel would otherwise play:
- At the waiting position, you register for the locking process using a push button or lever.
- A light signal shows when the lock has been prepared and entry is cleared.
- Once all waiting boats have entered and moored, the skipper who entered first usually triggers the actual locking process with a lever or button inside the chamber.
- Once the water level has equalized, the gates open automatically, and you can leave the chamber on the green exit signal.
The same basic rules apply at self-service locks as at staffed ones: let lines run freely, switch off the engine while waiting inside the chamber, and pay close attention to the instruction signs posted at the facility, since details can vary depending on how a particular lock is built.
Common Mistakes to Avoid
A frequent mistake is entering too fast, especially when the chamber already looks crowded. Just as risky is making a line fast around a bollard instead of paying it out by hand, one of the most common causes of dangerous situations in locks. Ignoring signals is another avoidable risk, for example entering on a still-red light because the gate already looks open enough visually. And finally, many recreational boaters underestimate how important it is to follow the lock personnel’s instructions immediately, even when they don’t seem to make sense at first glance.
How This Shows Up in the SBF Exam
Locks are part of the route-knowledge material (Streckenkenntnis) tested in the theory portion of the SBF Inland exam. Typical questions cover the meaning of the light signals, the priority relationship between commercial and recreational traffic, and the basic rules for mooring inside the chamber. The official ELWIS question catalog tests less about the technical workings of a lock and more about reliably recognizing the signals and understanding why certain behavioral rules exist. With the Boatpass app, you can practice exactly these questions in exam mode and immediately see where any gaps remain before it counts in the real SBF exam.
Conclusion
Navigating a lock feels unfamiliar the first time, but it follows a clear system: watch the signals, reduce speed, respect the priority of commercial traffic, and inside the chamber keep lines running freely instead of making them fast. Once you’ve internalized these basic rules, even unstaffed self-service locks stop being a source of stress, and you’ll move from one water level to the next safely and calmly.