The International Regulations for Preventing Collisions at Sea — the ColRegs, or IRPCS 1972 — establish a clear hierarchy for determining which vessel must give way in any encounter at sea. Understanding this hierarchy is not optional for offshore sailors: these rules have the force of law in every international water and in the territorial waters of every nation that has adopted them, which is essentially all of them.
The hierarchy is not based on the size of the vessel, the speed, or the confidence of the skipper at the helm. It is based on the vessel's ability to maneuver — and specifically, on which vessels are least able to get out of the way of others.
The Hierarchy of Vessels
ColRegs Rule 18 sets out the order of precedence. At the top are vessels that have effectively lost the ability to maneuver or are severely restricted. At the bottom are power-driven vessels under way in open water — the vessels with the greatest freedom to alter course and speed.
Vessels not under command (NUC) are vessels that through some exceptional circumstance are unable to maneuver as required by the rules — a vessel that has lost steering, suffered a machinery failure, or is otherwise incapacitated. A NUC vessel exhibits two all-round red lights at night (or two black balls by day) and must take no action to get out of anyone's way. Every other vessel must give way to it.
Vessels restricted in their ability to maneuver (RAM) are vessels engaged in work that limits their maneuverability — a vessel laying cable, conducting dredging operations, engaged in replenishment at sea, or towing when the tow severely restricts maneuvering. RAM vessels exhibit a vertical pattern of all-round lights: red, white, red. Like NUC vessels, they are not expected to maneuver; other vessels must keep clear.
Vessels constrained by their draft occupy a special category available only in certain areas and only when the vessel's draft relative to the available depth of water means that it genuinely cannot deviate from the channel. A deep-draft tanker in a shallow channel with no room to alter course to avoid a yacht is constrained by its draft. It exhibits three all-round red lights arranged vertically, or a cylinder by day. This category is frequently misunderstood — it does not apply to any large ship simply because it is large. It applies only when depth genuinely constrains course-keeping.
Vessels engaged in fishing — specifically, vessels using gear (trawls, nets, lines) that restricts their maneuverability — rank above sailing vessels and power vessels in the hierarchy. Note that a sportfishing boat with lines trailing does not qualify; this applies to commercial fishing vessels whose gear limits their ability to maneuver.
Sailing vessels — vessels proceeding under sail only, not using their engine — rank above power-driven vessels. A sailing vessel under sail and engine simultaneously is treated as a power-driven vessel for all ColRegs purposes.
Power-driven vessels under way are at the bottom of the hierarchy. They are expected to give way to all of the above. In practice, this means most recreational powerboats operating in open water are the give-way vessel in most situations.
The Critical Reality: Sailboats and Large Commercial Vessels
Here is the most important thing many sailors do not fully absorb: a sailing vessel under sail is not at the top of the hierarchy. It ranks above power-driven vessels but below NUC, RAM, constrained-by-draft, and fishing vessels. The practical consequence is significant.
A large tanker or container ship transiting a deep-water channel may well be constrained by its draft. If it is, the sailing yacht approaching on starboard tack does not have right of way over it. The yacht must give way. The same reasoning applies near traffic separation schemes, where large vessels following the scheme have limited ability to deviate, and small vessels — including sailing yachts — are required by Rule 10 to avoid impeding their passage.
Beyond the question of right of way is the simple question of physics. A fully laden supertanker at sea speed may require three miles and twenty minutes to stop. Its bridge is set back from the bow — the officer on watch may not even have a clear sight line to a small yacht 200 meters ahead. Knowing you are technically the stand-on vessel provides no protection if the other vessel cannot see you, cannot stop, and cannot maneuver. The prudent sailor treats every encounter with a large commercial vessel as one in which they should take positive action to open the distance, regardless of who technically has right of way.
Stand-On and Give-Way: What Each Requires
The ColRegs use two precise terms for vessels in a crossing or overtaking situation: the stand-on vessel and the give-way vessel.
The give-way vessel is required to take early and substantial action to keep well clear. Rule 16 states this explicitly: the give-way vessel shall take early and substantial action to keep well clear. "Early" means before the situation becomes tight. "Substantial" means large enough to be clearly apparent to the other vessel — a five-degree course change in the dark is not substantial. Rule 8 reinforces this: action taken to avoid collision shall be large enough to be readily apparent to the other vessel and shall result in passing at a safe distance.
The stand-on vessel is required to maintain its course and speed. This seems simple but carries a burden: the stand-on vessel must hold course so that the give-way vessel can predict its position and maneuver around it safely. Erratic alterations of course by the stand-on vessel, however well-intentioned, can cause collisions because the give-way vessel is planning its maneuver around the expected track of the stand-on vessel.
This is why experienced sailors give way early and decisively. The goal is not to demonstrate you know who has right of way — it is to create a situation that is unambiguous and safe for both vessels.
Sailboat vs. Sailboat: Port and Starboard Tack
When two sailing vessels approach each other, the tack they are on determines right of way. Rule 12 covers this in full.
When on different tacks: the vessel on port tack gives way to the vessel on starboard tack. Starboard tack means the wind is coming from the starboard (right) side; port tack means the wind is coming from the port (left) side. The starboard-tack vessel is stand-on; the port-tack vessel must take early action to keep clear.
When on the same tack: the vessel to windward gives way to the vessel to leeward. The leeward vessel — the one closer to the direction the wind is coming from — is the stand-on vessel. The windward vessel must keep clear.
There is one additional case: when a port-tack vessel cannot determine the tack of another vessel approaching from windward, it must treat the other vessel as being on starboard tack and give way. This prevents the ambiguous standoff where both vessels assume the other will maneuver.
Overtaking: Always Give Way
Rule 13 is clear: any vessel overtaking another is the give-way vessel, regardless of type. A sailing yacht overtaking a fishing vessel must keep clear. A powerboat overtaking a sailing yacht must keep clear. The overtaking vessel maintains give-way status until it is clearly past and clear of the overtaken vessel.
Overtaking is defined as approaching from a direction more than 22.5 degrees abaft the beam — roughly astern. If there is any doubt about whether you are overtaking, Rule 13 says you should assume you are, and give way accordingly.
Rule 2: The Responsibility Clause
ColRegs Rule 2 is sometimes called the "general prudence" rule, and it overrides the mechanical application of every other rule. It states that nothing in the ColRegs exonerates any vessel or owner or crew from the consequences of neglect to comply with the rules, or of neglect of any precaution that may be required by ordinary seamanship practice.
In plain terms: even the stand-on vessel has a responsibility. Rule 17 acknowledges this directly — when the stand-on vessel realizes that the give-way vessel is not taking appropriate action, the stand-on vessel may take action to avoid collision. Once it becomes apparent that a collision is unavoidable from the give-way vessel's inaction alone, the stand-on vessel shall take action.
The ColRegs create a structured priority system — but they do not create a world in which the technically correct vessel gets to hold course into a collision and claim innocence. Every mariner has a responsibility to avoid collision, and that responsibility exists regardless of who the rules say should have given way.