Rule 18 explains the obligations of vessels with restricted maneuverability

Outline

• What Rule 18 is about and what “restricted maneuverability” means

• Why this rule matters on the water

• How RAM vessels and other vessels should behave toward each other

• Real-world scenarios that bring Rule 18 to life

• Quick takeaways you can carry onto the deck

Rule 18: The rule about vessels with restricted maneuverability

Let’s cut to the point. Rule 18 in theCOLREGs covers the obligations of vessels that can’t maneuver as freely as others. Think of a tow dragging a barge, a vessel that’s hard to steer in rough seas, or a ship working in tight confines like a busy harbor mouth. These are vessels with restricted ability to take evasive action. The rule isn’t about passenger limits, fishing gear, or operating hours; it’s about how to share the water when one vessel can’t pivot or turn quickly enough to avoid a potential collision.

RAM – the idea behind the acronym

In COLREGs shorthand, the term RAM—restricted in its ability to maneuver—pops up a lot. RAM isn’t a fancy device or gadget; it’s a status. If you’re limited by the task you’re performing, the weather, the current, or the way you’re handling lines, you’re RAM for the moment. The key message of Rule 18 is simple: when you’re RAM, you must act to reduce risk. You should take steps that lessen the chance of collision while still carrying out your essential work. Meanwhile, the other vessels nearby have to recognize that limitation and adjust their own actions accordingly.

How RAM interacts with other vessels

Here’s the core idea in plain language: the RAM vessel should not crowd or block other ships more than necessary. It’s about giving space and time to the other vessel to pass or maneuver safely. The other vessel, in turn, should keep a lookout, slow down if needed, and plan a course that avoids forcing the RAM vessel into a difficult move. It’s a mutual handshake on the water, with the RAM vessel signaling intent through speed changes, course adjustments, or reducing engine power as appropriate. In practice, this means:

• The RAM vessel should move with predictable, deliberate actions rather than sudden swerves.

• Other vessels should not assume RAM will always “move out of the way” and should make early, clear decisions to avoid contact.

• Both sides stay alert to changing conditions—visibility, weather, traffic, or the RAM vessel’s task can shift the balance quickly.

If you’ve ever watched a towboat in a busy channel or a workboat edging a loading dock, you’ve seen Rule 18 in action without needing a textbook in your hands. The operators talk with the air of people who know the water can’t be surprised by sudden moves. They expect you to do the same: keep your situational awareness high and your actions steady.

Scenarios that bring Rule 18 to life

Because it helps to picture it, here are a few everyday situations where Rule 18 matters:

• A vessel towing a barge in a narrow channel. The tow’s length makes it hard to alter course quickly. Other traffic must give wide clearance and be prepared to slow down to let the tow pass safely.

• A vessel maneuvering in heavy seas or strong currents. If turning the helm is slow or the bow doesn’t respond fast, the ship ahead should reduce speed and use draw or drift to keep a safe distance.

• A vessel working in restricted visibility, like fog near a harbor entrance. With limited sight lines, RAM must stay conspicuous and avoid abrupt maneuvers; other vessels should proceed cautiously and keep safe speed.

• A ship performing line handling or mooring in a crowded area. The work itself can’t stop, but everyone around knows to back off a bit, give room, and avoid imposing new risks.

In all these cases, Rule 18 isn’t about rules that punish or penalize—it’s about safety through predictable behavior. It’s the common sense of seamanship that says, “I know you’ve got a job to do; I’ll adjust so we both get home safe.”

What this means for everyday navigation

Let’s connect the dots to something you might have on your radar charts or digital plotting tools. Rule 18 is about two pieces of navigation etiquette: visibility and predictability. If others can predict your actions, they can plan their own. If you know someone is RAM, you don’t gang up on them with an aggressive pass; you coordinate, slow down, and create a safe window for passage.

You’ll also notice the emphasis on communication. When appropriate, sound signals or lights can help convey intent. The radar screen and AIS displays add to the picture, giving you more time to react and more context for the decisions you make. Modern vessels aren’t just moving furniture; they’re moving data. The more you use that data—signals, watchkeeping, and speed changes—the safer the maneuver becomes.

A quick gut check for captains and skippers

• Do I know which vessels around me are RAM? If not, take a moment to evaluate and adjust.

• Am I signaling clearly through speed, course, or stance rather than abrupt moves?

• Is there enough distance to pass, considering the RAM vessel’s constraints?

• If weather or traffic worsens, can I reduce speed sooner rather than later?

These are not fancy rules on a shelf; they’re practical habits you can bring up on the bridge or in the cockpit.

A few notes on what Rule 18 is not

You’ll notice some confusion around this rule because it sits among several that regulate vessel behavior. It can be tempting to think RAM means “I’m in the clear, you handle it,” but that’s not the spirit. Rule 18 doesn’t grant special right of way to RAM. It sets expectations for how RAM and other vessels should coordinate. It’s not about who has the power to go first; it’s about who has the time and space to avoid a collision.

Likewise, Rule 18 doesn’t spell out every single operating scenario in great detail. It gives guiding principles: prevent collisions, act with care, and communicate intentions. The practical takeaway is simple: be predictable, be courteous, and be ready to adapt as conditions change. In the end, safe navigation relies on shared responsibility.

Putting it all together with a few practical tips

• Keep a rolling lookout for RAM vessels, especially in busy routes or near confined waters.

• If you’re the RAM vessel, plan your next moves a few seconds ahead; avoid sudden swings.

• Use engine room and helm signals to clarify intent when visibility is limited.

• When in doubt, slow down a notch and give extra room. It’s cheaper in the long run than a close-quarters incident.

• Reference your local nautical charts and stay aware of temp changes in current and wind, which can turn a manageable maneuver into a tricky one.

A friendly closing thought

Rule 18 isn’t the flashiest part of the COLREGs, but it’s one of the most practical. It asks us to respect the limits of each vessel and to cooperate in the shared space that is the waterway. When a ship tows a barge, when a dredge works the harbor mouth, or when fog wraps the coastline in a chill hush—Rule 18 reminds us to keep it human, keep it deliberate, and keep the momentum toward safe passage.

If you’re reading this with pro-level readiness in mind, you’ll recognize the clarity of this rule in action. It’s not about clever tactics; it’s about steady, thoughtful navigation that reduces risk for everyone aboard. And that, after all, is what good seamanship is all about: staying aware, staying patient, and letting careful planning do the heavy lifting.

Final takeaway: Rule 18 is the backbone for interactions with vessels that can’t maneuver as easily. Respect their constraints, anticipate their needs, and coordinate your actions so the water stays a safe place for all who travel it.