Official rule text as published in the U.S. Coast Guard Navigation Rules
Every vessel which is directed to keep out of the way of another vessel shall, so far as possible, take early and substantial action to keep well clear.
MyCOLREGS explanation
Summary
If you're the give-way vessel, don't wait and don't make a token gesture - take action early enough and big enough that the other vessel can see clearly what you're doing, so you end up well clear of her.
Real World Example
A turn too small or too late does worse than nothing: the stand-on vessel is watching for a change she can actually recognize, and an ambiguous nudge can burn the time she needed to react if you'd simply held your original course instead.
Practice Questions
Q1. You realize 10 minutes out that you'll need to give way. Which better satisfies Rule 16 - one clearly noticeable course change made now, or a long string of small, barely-perceptible nudges spread over the next several minutes so your own course isn't disrupted much?
A. The string of small nudges, since Rule 16 only requires that you eventually end up clear, however gradually, and doesn't concern itself with how the other vessel perceives your maneuvering.
B. Either approach is fine, since Rule 16 doesn't address how obvious a maneuver needs to be, only when it happens relative to the developing risk of collision.
C. The one clear change, because Rule 16 requires action that's positive and large enough to be readily apparent to the other vessel, not a maneuver so subtle it could go unnoticed.
D. The small nudges, because a single obvious course change risks confusing the other vessel about your intentions and could itself trigger an unnecessary evasive maneuver on her part.
Q2. A give-way vessel makes a two-degree course change at the last possible moment before the vessels close. Does this satisfy Rule 16?
A. No, because Rule 16 requires her to stop engines entirely.
B. Yes, as long as she also sounds one short blast.
C. Yes, because any course change counts as give-way action.
D. No, because Rule 16 requires early and substantial action, not a late, minimal change.
Practice Question Answers
Q1.
C. Early and substantial, taken so far as possible to keep well clear. Rule 16 requires the give-way vessel to take early and substantial action, so far as possible, to keep well clear. A has the give-way vessel waiting to act, which is the opposite of "early." B describes the smallest possible action, the opposite of "substantial." D treats the duty as optional, when Rule 16 imposes it directly on the give-way vessel.
Q2.
D. No, because Rule 16 requires early and substantial action, not a late, minimal change. A late, barely perceptible course change fails both the "early" and "substantial" requirements Rule 16 sets for give-way action. A demands something Rule 16 doesn't require. B assumes a sound signal can substitute for actually maneuvering. C treats any course change as sufficient, when the rule specifically requires it be early and substantial - a late, tiny change fails on both counts.