Many boaters underestimate their own bow and stern wave. What looks harmless from the cockpit can slam a moored boat against the pilings at a dock, throw a stand-up paddler into the water, or put a canoeist in trouble. Wake and suction are not a trivial matter: there are clear rules, and whoever causes damage is liable for it. This article explains what wake and suction really are, what the regulations require, and who is on the hook when something goes wrong.

What Wake and Suction Do

Every moving boat displaces water and produces two effects. The wake (or wash) is the visible bow and stern wave that spreads out to the sides. The suction is the less visible pulling effect that arises when the water alongside and behind the boat is set in motion. Both can cause considerable damage:

  • Moored boats slam against docks, pilings, or neighboring boats; fenders and lines are overloaded.
  • Docks, landing stages, and shore reinforcements suffer from repeated wake; on natural banks it accelerates erosion.
  • Small craft such as canoes, rowing boats, SUP boards, or small sailing dinghies can capsize or swamp.
  • Swimmers are endangered, especially near the shore.
  • On board itself, an unexpected wave can knock people off their feet or throw objects overboard.

The effect is especially strong in narrow channels, in harbors, and near berths, because the wave cannot run out but hits obstacles directly.

The Rule: Avoid Wake (§ 6.20 BinSchStrO)

On German inland waterways, avoiding wake is explicitly regulated. Under § 6.20 of the inland waterways regulations (BinSchStrO), a vessel must set its speed so that wake or suction capable of causing damage to a stationary or moving vessel, a floating body, or an installation is avoided. Speed must be reduced in good time, but not below what is necessary for safe steering.

The rule names situations calling for particular care, among them:

  • before a harbor entrance,
  • near a vessel moored to the bank or a landing stage, or one that is loading or unloading,
  • near a vessel lying at a usual berth,
  • near a ferry that is not moving freely,
  • on stretches marked by the corresponding waterway signs.

In short: where damage is possible, you have to come off the throttle early enough that your wave is already small by the time it reaches the obstacle. Braking too late does not help, because the wave you have already created keeps running.

Suction: The Underestimated Hazard

While wake is visible, suction is often overlooked. If you pass close to a smaller boat, a SUP, or a swimmer, the pulling effect can draw them sideways toward your boat and throw them off balance. Large displacement vessels create particularly strong suction, but fast sportboats also have a noticeable effect near the shore.

The simplest countermeasure is distance: the wider you pass other water users, the less they feel the wave and the suction. If you have to pass close, slow down early, not just when you are level with them.

At Sea: Safe Speed and Consideration

On coastal waterways there is often no fixed speed limit as on many inland waters. But that does not mean wake is irrelevant there. Safe speed under COLREGs Rule 6 and the principle of good seamanship apply: you must handle your boat so that you do not avoidably endanger or damage anyone. Even along the coast, your wake can hit moored boats in a marina, tenders, or swimmers. Consideration is therefore not purely an inland issue.

Who Is Liable for Wake Damage?

In the event of damage, the party that caused it pays. Whoever causes damage through their wake or suction is generally liable for it under civil law, meaning they have to pay for the damage caused. This can apply to the neighboring boat slammed against the dock as much as to damaged installations or the consequences of a capsized small craft.

On top of that comes the public-law side: breaching the duty to avoid wake can be treated as a regulatory offense and fined. The two can coincide, the fine for the rule breach and civil liability for the damage. A suitable boat liability insurance policy usually covers such damage, which is why it makes sense for recreational boaters. For which other offenses on the water can get expensive, see the article on fines and offenses on the water.

A practical point: in a dispute, what matters is whether the wake was avoidable. So it pays to boat in an anticipatory and demonstrably considerate way, especially in critical areas such as harbors and berths.

How to Avoid Wake and Suction

A few habits keep your wave small and your boating considerate:

  • Come off the throttle in good time: reduce speed early, not only when level with the obstacle. Your wave needs time to shrink.
  • Keep your distance: pass moored boats, canoes, SUPs, and swimmers with as much distance as possible.
  • Avoid the transition zone: the range between displacement and planing speed often creates the biggest wave. Either go slowly in displacement mode or plane cleanly, where allowed and sensible.
  • Look astern: watch your own stern wave and where it runs, especially near the shore.
  • Mind the signs: observe speed limits and signs put up to avoid wake.

Anyone who has the collision and conduct rules down cold handles tight situations more confidently. A good foundation for that is preparing for the SBF Inland license.

Conclusion

Wake and suction are more than a question of courtesy. On German inland waterways, § 6.20 BinSchStrO explicitly requires setting your speed so that harmful wake is avoided, and at sea, safe speed and good seamanship apply. Whoever causes damage is liable for it and additionally risks a fine. The good news: with early throttle reduction, enough distance, and an eye on your own stern wave, most of it is easy to avoid.

The Boatpass app helps you learn the traffic rules on the water reliably, from avoiding wake to the right-of-way rules, with the official exam questions and a realistic exam mode, so that you travel considerately and by the book.