COLREGs Rule 17: Action by stand-on vessel — Explained

Rule 17 says the stand-on vessel keeps its course and speed, may act once it is clear the give-way vessel is not acting, and must act when collision can no longer be avoided by the give-way vessel alone.

What Rule 17 says

When one vessel must keep out of the way, the other keeps her course and speed.
The stand-on vessel may act to avoid collision by her own manoeuvre as soon as it becomes apparent that the give-way vessel is not taking appropriate action.
When so close that collision cannot be avoided by the give-way vessel alone, the stand-on vessel shall take the action that will best help avoid collision.
A power-driven stand-on vessel acting in a crossing situation should, if circumstances admit, not alter course to port for a vessel on her own port side.
None of this relieves the give-way vessel of its obligation to keep out of the way.

This is a plain-English summary, not the official wording. For the exact text, see the IMO convention. In UK waters the rules are given legal force by the Merchant Shipping (Distress Signals and Prevention of Collisions) Regulations.

What it means on a yacht

Holding course and speed lets the give-way vessel predict you. If a ship is not responding, call it on VHF, sound five short blasts, then act. Turning to port towards a vessel on your port side often turns a near-miss into a collision.

Practise it

Test yourself on who gives way in the free COLREGs trainer, or print the rules of the road cheat sheets for the chart table.

Other rules in Part B

Frequently asked questions

What should the stand-on vessel do?

Keep its course and speed. It may take action once it is clear the give-way vessel is not doing so, and must act if collision cannot be avoided by the give-way vessel alone.