Does the bigger ship have right of way? A motorboat and a cargo ship under the COLREGs

Published on 15 October 2026 · By Ricard Prehn, professional recreational skipper (PPER), Spanish Yacht Captain (capitán de yate), Yacht Captain up to 200 GT and sailing instructor for over 27 years

Size does not give you right of way at sea

It is the answer we hear most in class: “the big one, she can’t manoeuvre”. But the COLREGs (the International Regulations for Preventing Collisions at Sea, called RIPA in Spain) do not mention length in the steering and sailing rules. They share out priority in two ways:

• By type of vessel (Rule 18): not under command and restricted in ability to manoeuvre at the top, then fishing, then sail and, last, power-driven vessels.
• By situation, when both are the same type: crossing (Rule 15), head-on (Rule 14) and overtaking (Rule 13).

A 6-metre motorboat and a 200-metre container ship are, as far as the rules are concerned, the same thing: two power-driven vessels. So when they cross, Rule 15 applies and size makes no difference. There is more detail in what COLREGs are and who has right of way.

A motorboat and a cargo ship crossing: the ship gives way

Rule 15 says that when two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side keeps out of the way. In the video, the motorboat is on the ship’s starboard side: the ship is the give-way vessel, and the motorboat keeps her course and speed.

An easy way to remember it, day or night: if you can see the other vessel’s red light (her port side), she is on your starboard side and you give way. If you see her green, you stand on and keep watching. At night you cannot see size, only lights, so the rule is the only clue you have. Each vessel’s lights are in navigation lights.

Try it in the encounter simulator from our online classroom: change who is coming from where and see who must give way.

How to tell if you are going to collide: the bearing

In the video you can see it with the lines on the water: if both projections reach the same spot at the same time, you collide. At sea there are no lines, but one trick always works: the bearing.

Line the other vessel up with a stanchion, or take her bearing with a hand-bearing compass, and repeat it every minute. If the bearing does not change and the distance is closing, you are on a collision course (Rule 7). If she is drawing aft or ahead of you, you are not.

With a cargo ship there is a catch: she is 200 metres long, so even if her bearing changes a little there may still be a risk. The rules say so explicitly for very large vessels at close range. When in doubt, treat it as a risk of collision.

Being the stand-on vessel does not save you: do not trust it

The stand-on vessel does not just watch. Rule 17 asks her to keep her course and speed, but also to take action if the other vessel is clearly not doing so, and to act no matter what once collision can no longer be avoided by the give-way vessel alone. With a cargo ship there are plenty of reasons not to trust it:

• The officer of the watch has fallen asleep, or is alone on the bridge and busy with something else.
• They are distracted: paperwork, a phone, a call, looking at the wrong screen.
• Their radar and AIS have not picked you up. A GRP motorboat gives a very weak radar echo (that is why you carry a reflector), and many small boats have no AIS.
• They cannot see you under the bow. On a loaded container ship, the area hidden from the bridge can reach hundreds of metres ahead (the rules allow up to 500 m).
• Even if they see you, they are slow to react. A ship like that needs a lot of distance to turn or stop.

First, call them on the radio

Before things get tight, call them. On channel 16, the calling channel, and as soon as they answer move to a ship-to-ship working channel such as 6:

“Ship heading north, one mile west of Port Garraf, this is the white motorboat on your starboard side. Do you have me on radar? Over.”

If you can see her name on AIS, use it: you will get an answer much sooner. Spell out what you need with the phonetic alphabet and, if she does not answer, remember she may not be hearing you: with a 5 W handheld, VHF range is short.

If she neither answers nor acts, you get out of the way

If the ship neither answers nor alters course, you get out of the way, and in good time:

1. A large, clear alteration to starboard, obvious from the bridge (Rule 8). No 5-degree nudges.
2. Slow down or stop if needed and let her cross ahead: you pass astern of her.
3. Never to port. If at the last moment she turns to starboard, as the rules ask her to, you would meet.
4. If you cannot tell what she is doing, five short, rapid blasts: the doubt signal.

Better to lose five minutes than argue with 200 metres of steel about who was right.

When does the big ship have priority?

There are cases where the small boat gives way even if the big ship is on her port side. Always check the shapes (by day) and lights (at night) she shows:

Situation	By day	At night	What you do
Restricted in ability to manoeuvre (dredger, underwater work, difficult tow)	ball · diamond · ball	red · white · red	Keep out of the way
Not under command (breakdown)	two balls	two reds	Keep out of the way
Constrained by her draught	a cylinder	three reds	Do not impede her passage
Narrow channel or traffic separation scheme	—	—	If you are under 20 m or under sail, do not impede her
You are overtaking her	—	—	You keep out of the way (Rule 13)

In the video, the ship shows no shapes at all: she is an ordinary power-driven vessel, which is why Rule 15 applies.

Frequently asked questions

Does the bigger vessel have right of way at sea?

No. The COLREGs give no priority by size. When two power-driven vessels are crossing, the one with the other on her starboard side keeps out of the way, whatever their length. Size only matters in specific cases: narrow channels, traffic separation schemes or a vessel constrained by her draught.

If a cargo ship is on my port side, who gives way?

She does. If you see her on your port side, you are on her starboard side, so the ship must keep out of the way (Rule 15). You keep your course and speed, but keep watching: if she does not act, call her on the radio and, if needed, manoeuvre yourself to starboard and slowing down, never to port (Rule 17).

How do I know if there is a risk of collision?

Take her compass bearing several times. If the bearing does not change and the distance is closing, there is a risk of collision (Rule 7). With a very large vessel or at close range, risk may exist even when the bearing changes a little, because her bow and stern are hundreds of metres apart.

What shapes does a vessel restricted in her ability to manoeuvre show?

By day, three shapes in a vertical line: ball, diamond, ball. At night, three all-round lights in a vertical line: red, white, red. If she shows them, she has priority over a power-driven vessel even if she is on your port side (Rule 18).

Which VHF channel do I use to call a ship?

Channel 16, the calling channel, and as soon as she answers you move to a ship-to-ship working channel such as 6. Call her by name if you can see it on AIS, or by course and position ("ship heading north, one mile west of…"), and say who and where you are.

Which way do I turn if the ship does not act?

To starboard, with a clear, early alteration, slowing down or stopping if needed so you pass astern of her. Never to port if she is on your port side: you could meet if she turns to starboard at the last moment (Rule 17). If you are unsure of her intentions, sound five short, rapid blasts.