COLREGS Rule 17 — Action by Stand-on Vessel

Rule Text

What it means on the water

• →Stand-on vessel: initially must maintain course and speed.
• →May take action (Rule 17(a)(ii)) when it becomes apparent the give-way vessel is not acting.
• →Must take action (Rule 17(b)) when collision cannot be avoided by the give-way vessel's maneuver alone.
• →Shall not alter course to PORT for a vessel on its PORT side (to avoid compounding the risk).
• →If in a close-quarters situation, both vessels may need to act — Rule 17 does not create a shield.

Common exam mistakes

• ✗Thinking the stand-on vessel can NEVER maneuver — it may act when the give-way vessel fails to, and must act when necessary.
• ✗Missing the prohibition on altering course to port for a vessel on the port side.
• ✗Confusing 'may take action' (Rule 17(a)(ii)) with 'shall take action' (Rule 17(b)) — these are different thresholds.

USCG exam questions — Rule 17

These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.

1. 1. Two sailing vessels are approaching one another so as to involve risk of collision. Vessel A has the wind on her port side. Vessel B has the wind on her starboard side. Which vessel is the give-way vessel?

   • A.Vessel A, because she has the wind on the port side✓
   • B.Vessel B, because she has the wind on the starboard side
   • C.The vessel that is more close-hauled
   • D.The vessel to leeward

   Why: Rule 12(a)(i) states that when each sailing vessel has the wind on a different side, the vessel with the wind on the port side shall keep out of the way. Vessel A has the wind on port; she gives way. The close-hauled state and leeward position are irrelevant to this specific sub-rule.

2. 2. A sailing vessel sees another sailing vessel to windward but cannot determine whether that vessel has the wind on the port or starboard side. Under Rule 12, the vessel to leeward shall:

   • A.Sound five short blasts and maintain course and speed
   • B.Keep out of the way of the vessel to windward✓
   • C.Assume the other vessel is on starboard tack and give way accordingly
   • D.Reduce speed until the windward vessel's tack can be determined

   Why: The keyed answer is correct: under Rule 12(a)(iii), if a vessel with the wind on the port side sees a vessel to windward and cannot determine with certainty whether that vessel has the wind on the port or starboard side, she shall keep out of the way of the other. This is a safety default for the leeward (port-tack) vessel, requiring her to give way to the windward vessel. (Note: Rule 12(b) is the separate definition of the "windward side" — the side opposite that on which the mainsail is carried — and does not govern this ambiguous-tack situation.)

3. 3. A vessel that is overtaking another begins to draw abeam and eventually moves ahead. At what point does the overtaking obligation end under Rule 13?

   • A.When the overtaking vessel is clearly past and well clear of the overtaken vessel✓
   • B.When the overtaken vessel can see the overtaking vessel's sidelights
   • C.When the overtaking vessel sounds two short blasts to indicate she is clear
   • D.As soon as the overtaking vessel crosses ahead of the overtaken vessel's bow

   Why: Rule 13(d) states that the overtaking vessel shall keep clear until she is finally past and clear. The obligation persists through the entire overtaking maneuver — there is no intermediate point where the give-way duty switches. The 'past and clear' standard is intentionally high to prevent premature assumption that the maneuver is complete.

4. 4. Under Rule 14(b), a head-on situation shall be deemed to exist when a vessel sees another vessel ahead and:

   • A.The other vessel's masthead lights are in line and her range lights can be seen
   • B.At night, she can see the masthead lights of the other vessel in a line or nearly in a line, or both sidelights✓
   • C.The bearing to the other vessel does not change over a 3-minute period
   • D.Both vessels are on courses within 10 degrees of each other

   Why: Rule 14(b) specifies the visual indicators of a head-on situation at night: masthead lights in line (or nearly in line) and/or both sidelights visible. This is the practical way mariners identify the head-on meeting without requiring precise course comparison.

5. 5. Rule 15 adds that, where possible, the give-way vessel in a crossing situation shall avoid:

   • A.Reducing speed, which could confuse the stand-on vessel
   • B.Crossing ahead of the other vessel✓
   • C.Altering course to starboard when the other vessel is on her starboard side
   • D.Sounding any signal that could be misinterpreted

   Why: Rule 15 states that the give-way vessel shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel. Passing astern is the preferred maneuver; crossing ahead risks collision if the give-way vessel underestimates the closing speed or the stand-on vessel maintains speed.

6. 6. Under Rule 17(a), the stand-on vessel in a crossing situation shall:

   • A.Immediately alter course to port to open the CPA
   • B.Immediately reduce speed to allow the give-way vessel more time
   • C.Maintain her course and speed✓
   • D.Sound five short blasts and then take independent action

   Why: Rule 17(a)(i) obliges the stand-on vessel to maintain course and speed. This predictability is essential — the give-way vessel plans its maneuver based on the stand-on vessel continuing unchanged. Unpredictable early action by the stand-on vessel can negate the give-way vessel's avoidance.

7. 7. Under Rule 17(b), when a stand-on vessel finds herself so close to the give-way vessel that collision cannot be avoided by the give-way vessel alone, the stand-on vessel shall:

   • A.Maintain course and speed to avoid confusing the give-way vessel
   • B.Sound five short blasts and reduce speed
   • C.Take such action as will best aid to avoid collision✓
   • D.Alter course to starboard regardless of the position of the give-way vessel

   Why: Rule 17(b) converts the stand-on vessel's permission into a duty once collision cannot be avoided by the give-way vessel alone. At that point the stand-on vessel must take whatever action best avoids collision — this is the in-extremis provision. The specific action depends on circumstances; starboard is not always the answer.

8. 8. Under Rule 13, any vessel overtaking any other vessel shall:

   • A.Keep out of the way of the vessel being overtaken✓
   • B.Sound one prolonged blast to signal her intention to overtake
   • C.Proceed at a speed sufficient to complete the overtaking in minimum time
   • D.Overtake only on the starboard side of the vessel ahead

   Why: Rule 13(a) places an absolute duty on the overtaking vessel to keep out of the way of the vessel being overtaken, regardless of any other rule that might otherwise apply. Rule 13 overrides the head-on and crossing rules — once in the overtaking sector, Rule 13 governs.

Frequently asked questions

When can the stand-on vessel take action to avoid a collision?

The stand-on vessel may take action as soon as it becomes apparent the give-way vessel is not taking appropriate action (Rule 17(a)(ii)). It must take action when it becomes clear that collision cannot be avoided by the give-way vessel alone (Rule 17(b)). In both cases, the action should best aid in avoiding collision.

What course change is the stand-on vessel prohibited from making?

The stand-on vessel shall not, so far as possible, alter course to port for a vessel on her own port side. This is because altering to port in that situation tends to close the distance rather than open it, increasing rather than decreasing the risk.

All COLREGS rules