Rule 6 explains how to keep a safe speed to avoid collisions at sea

Rule 6: The speed that keeps you safe

Let’s set the scene. You’re steering a small vessel along a busy stretch of coastline, or maybe threading a path through a busy channel at dusk. The water’s a little choppy, the light is fading, and other ships—big and small—are doing their thing in the same space. In moments like this, Rule 6 isn’t about fancy equipment or clever tricks. It’s about something simpler, something fundamental: how fast you should go so you can avoid a collision.

What Rule 6 actually says

The essence of Rule 6 is straightforward: every vessel must proceed at a safe speed, one that lets you take proper and effective action to avoid a collision if it starts to look likely. In other words, speed that leaves you enough time and room to maneuver, to slow down, or to stop if another ship’s movements force a change of plan.

That “safe speed” isn’t a single number. It’s a judgment call shaped by the situation. It hinges on what you can see, what you can hear, and what you can feel through the helm and the wheel. It’s also intimately tied to how your vessel can respond—how quick you can turn, how quickly you can slow, and how long it takes to halt or alter course.

Key factors to weigh, in plain terms

Rule 6 asks you to consider a handful of practical realities. Here are the big ones:

• Visibility: If you’re staring into fog, rain, or twilight, your ability to detect other vessels early changes. The poorer the visibility, the slower you should go to preserve a margin of safety.

• Traffic density: In a crowded harbor or a tight channel, more ships sharing the same airspace means you’ll need to reduce speed to give yourself or others space to maneuver.

• Your vessel’s maneuverability: Some boats respond quickly to a turn; others take longer to steer and stop. Heavier ships generally need more distance to adjust shape and speed.

• Background light at night: City lights, shore lights, or the glow of a coastline can obscure the presence or bearing of other vessels. A well-lit background often requires slower speeds to keep reaction time reasonable.

• Sea state and wind/current: Choppy seas, swells, or current can affect how steady your vessel is and how long it takes to change direction or stop. Rough water often means you’ll want to ease off the throttle.

• Distance to other vessels: If another boat is within apparent range and may pose a risk, you’ve got to lower speed so you can anticipate and respond as needed.

• Draft and channel constraints: If you’re close to a shallow area or a narrow channel, your ability to maneuver safely is constrained, which usually means watching speed more carefully.

Let me explain it with a simple mental image. Think of safe speed like driving a car through a busy intersection without traffic lights on. If you can clearly see a gap and know you’ll have time to brake or steer around an obstacle, you might be cruising a bit. If the intersection is crowded, or you can’t see far ahead, you slow down to give yourself time to react. The same logic applies on the water, just with different gear and channels of navigation.

What Rule 6 is not about

It’s easy to mix this up, especially when you’re surrounded by other rules about navigation. But Rule 6 isn’t a blanket checklist for everything a vessel needs to do. It doesn’t set minimum crew levels. It doesn’t dictate weather assessments before you cast off your lines. It doesn’t specify engine specifications or how fast a particular engine can push you. Those items have their own places in the broader body of navigation rules and guidelines.

Rule 6 is specifically about maintaining a speed that enables proper and effective action to avoid collision. The point is safety through judgment and timing, not a one-size-fits-all number. The right speed can be different for your boat, the water you’re in, and the other boats that share the space.

Putting Rule 6 into everyday practice

So how does this work when you’re actually at the helm? Here are a few practical habits that align with Rule 6, without turning navigation into guesswork:

• Keep a dynamic speed mindset: Don’t lock your speed into a single setting. Be ready to adjust as visibility changes, or as traffic patterns shift.

• Scan and anticipate: A good lookout isn’t just about spotting other vessels; it’s about anticipating their possible maneuvers. If another boat looks like it might cross your bow, ease off a touch sooner rather than later.

• Use space, not speed alone: Sometimes the best move is to slow down, create distance, and give yourself options. It’s not always about arriving sooner; it’s about arriving safely.

• Account for take-action time: Remember your vessel may not react instantly. Your steering input and braking (or slowing) take time to produce a result. Factor that delay into your speed choice.

• Leverage aids, wisely: Radar, chart plots, and AIS can help you gauge traffic and distance. But never rely on tools alone. The human estimate—your judgment—still matters most.

• Practice safe speed across conditions: In restricted visibility, stay well below your comfortable speed. In bright, open water with light traffic, you might be able to move a bit quicker—but not recklessly.

• Regularly refresh your situational awareness: Habits like a quick pre-sail mental check of weather, tide, traffic, and possible escape routes keep Rule 6 alive in your decisions.

Real-world scenarios that breathe life into Rule 6

Scenario 1: Fog at first light in a coastal channel

You’re threading a channel where the shoreline is a pale smear and the water looks glassy. Visibility is limited to a fraction of a mile. A vessel ahead seems to appear and vanish with the fog. The prudent move is to slow down and be prepared to alter course or stop if necessary. The goal isn’t to rush through the fog but to keep a safe cushion so you can react if that oncoming boat reveals itself.

Scenario 2: Nighttime in a busy harbor

You’re maneuvering near the marina at dusk. Background lights from the city, boats’ deck lights, and the reflections on the water can make other vessels harder to judge. You’d keep your speed lower than your daytime pace, not out of fear but out of prudence. You give yourself time to notice a moving light on the horizon, a shadowy outline, or a sudden turn by a nearby vessel. It’s not about slow-to-a-slog; it’s about purposeful, measured speed that keeps options open.

Scenario 3: Open sea, moderate chop, a crossing risk

Out in open water with a light chop, you’re approaching a crossing situation where another vessel’s bearing could bring it close. Here, your speed should be sufficient to execute a clear maneuver if needed but not so fast that you eliminate your own room for action. You’re balancing visibility, the other vessel’s likely path, and your own boat’s turning radius.

Why Rule 6 matters in the broader ethic of seafaring

Rule 6 isn’t just a dry inscription. It embodies the spirit of safe navigation: make speed a tool for safety, not a weapon for hurry. When mariners keep a careful, adaptable pace, collision risk drops. This rule works hand-in-hand with other COLREGs that emphasize good seamanship—constant lookouts, clear communications, predictable action, and respect for other vessels’ rights of way. It’s a collaborative dance on the water, where speed isn’t the star, but a key ally in safe passage.

A few practical takeaways you can carry to any voyage

• If you’re unsure whether your speed is safe, slow down a notch. You can always add back speed later if the situation clarifies.

• When visibility or traffic ramps up, tune your speed down. The more you can see and anticipate, the more confident you’ll feel about maneuvering.

• Remember that “safe” is situational. The same boat in calm water with a clear horizon isn’t in the same boat as a vessel in a fog bank with a crowded channel.

• Use your eyes as your best instrument, then confirm with instruments. Don’t rely on one sense or tool alone.

• Talk calmly, even if you’re alone at the helm. A quiet, deliberate approach reduces the chance of overcorrecting or overreacting.

Bringing it back to the main point

Rule 6 isn’t a laundry list of what to do; it’s a philosophy for sharing the sea safely. The main principle—maintain a speed that lets you take proper and effective action to avoid a collision—frames decisions from the moment you cast off until you tie up at the destination. The factors it invites you to weigh are practical, experiential, and often visceral. Visibility, traffic, maneuverability, night-time background light, and the sea’s mood all press on your judgment, nudging you toward a pace that feels just right for the moment.

If you’ve ever found yourself glancing at a horizon that’s both alluring and uncertain, Rule 6 helps you translate that sense into smart pacing. It’s not about racing to the end of a voyage; it’s about arriving safely, with options still open and a clear-headed sense of responsibility to the other people and vessels sharing the waterway.

A final thought to buoy your navigation mindset

The sea has a way of reminding you that speed is not the prize—it’s a tool. The real victory is staying in command of your craft, making thoughtful choices, and adjusting as the story unfolds around you. Rule 6 gives you a compass for that mindset: sail at a safe speed, stay attentive, and be ready to act when the moment calls for it. That’s the kind of practice that keeps you steady, shipshape, and ready for whatever the next stretch of water might bring.