Drawbridges, Inland
Requesting a drawbridge opening
Please open the draw.
One prolonged blast, then one short blast
Who sounds it
Vessel requesting a drawbridge to open.
How it's sounded
"One prolonged blast followed by one short blast sounded not more than three seconds after the prolonged blast." Prolonged: 4 to 6 seconds. Short: approximately 1 second (33 CFR 117.15(b)(2)). 1 second is used for the gap.
Repeated until acknowledged in some manner by the drawtender.
A short blast is about 1 second. A prolonged blast is 4 to 6 seconds. Clips use 1 and 5 seconds.
Worth remembering
33 CFR 117.15 applies at U.S. drawbridges. It's separate from the Navigation Rules, and rules for a specific bridge in Part 117 Subpart B can differ. The same signals can go by radio.
The same sound elsewhere
These use the same pattern, so the rules you’re under and the situation decide what it means.
More in drawbridges
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Helm is an independent study aid, not affiliated with or endorsed by the U.S. Coast Guard or the National Maritime Center. This page is for study, not navigation guidance or legal advice. Check the current rules before you rely on anything here.