A yacht travelling down a channel, half a mile wide, would probably not consider itself to be in a narrow channel. If a ship were to travel along the channel at the same time, the yacht would probably find the channel very narrow!
So the judgement for this rule is based on the sizes of the vessels involved and the available water. In many cases it may be prudent for a small craft to stay just outside the channel, there is often plenty of depth as buoyage is mainly positioned for large ships, however, always check the chart first.
In any case this rule states that a sailing vessel and a vessel of less than 20m shall not impede a vessel which can only use the channel. This is one of several situations where the general rule of power giving way to sail does not apply.
It is also common sense not to anchor in a narrow channel if this would cause a hazard to other traffic.
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