When vessels are in sight of one another, what is the meaning of sounding FIVE or more short and rapid blasts on the whistle under COLREGs Rule 34(d)?

1. The doubt/danger signal: indicates that a vessel fails to understand the intentions or actions of the other, or doubts whether sufficient action is being taken to avoid collision
2. The vessel is preparing to drop anchor immediately
3. The vessel is overtaking on the starboard side
4. The vessel has caught a large school of fish and requires assistance