To ask a drawbridge to open by sound, give one prolonged blast of four to six seconds, then one short blast of about one second, then wait for the bridge tender to answer. A battery train horn produces that signal easily. The hard part is the timing, plus knowing when you are not allowed to ask at all.
The Federal Signal: One Prolonged, One Short
Drawbridge signals are set nationwide by the Coast Guard in 33 CFR 117.15. The rule lets you request an opening three ways: a sound signal, a visual signal, or a radio call. Whichever you use, you have to keep signaling until the drawtender acknowledges you, and you do not proceed before that.
The regulation defines both blasts in seconds, so there is no guesswork:
| Signal | Who sounds it | What it means |
|---|---|---|
| 1 prolonged (4–6 sec) + 1 short (about 1 sec), with the short blast no more than 3 sec after the long one | Your boat | Please open the draw |
| 1 prolonged + 1 short, within 30 sec of your request | Bridge tender | Request received. The draw will open now. |
| 5 short blasts in rapid succession, within 30 sec of your request | Bridge tender | Cannot open right now, or the draw is open and about to close. Stop and stand by. |
| 5 short blasts in rapid succession | Your boat | Request to open during a scheduled closure period. Only for vessels the rules require the bridge to pass at those times. |
The rule also covers the visual version. A boat may raise and lower a white flag, or a white, amber or green light, vertically. A tender who can't open swings a red flag or light horizontally, or shows a fixed or flashing red light. If the tender answers with five shorts, the rule says they keep repeating it until you acknowledge in some way. A wave from the helm or a reply on the radio works.
Does a Battery Train Horn Count as a Legal Signal Device?
Yes. Section 117.15(b)(1) says sound signals "shall be made by whistle, horn, megaphone, hailer, or other device capable of producing the described signals loud enough to be heard by the drawtender." The rule doesn't specify a decibel level, a pitch, or a type of horn. What matters is that the tender can hear the blasts and can tell a long one from a short one.
That suits a battery train horn. It has a pull trigger, so you decide exactly when each blast starts and stops, and a five-second prolonged blast is simply a five-second pull. Volume is the other half: our dual-trumpet models are rated at 130 dB, which leaves plenty of margin over wind and engine noise when the bridge house is a few hundred feet away.
A battery horn is portable, but it is a different kind of horn from the one you may need to meet the boat-carriage rules. Federal navigation rules separately require recreational boats to carry a means of making an efficient sound signal. We cover how a battery horn fits those requirements in our guide to USCG sound-signal requirements for boats. Opening a drawbridge is just one of the jobs that horn does.
How to Sound It Cleanly with a Trigger Horn
Most bad bridge signals are timing errors. The long blast gets cut off at two seconds, or there is a long pause before the short one. Here is how to get it right every time:
- Use the trigger, not a guess. Hold the horn in your hand at the helm and pull the trigger for the long blast. You control the start and stop exactly, which is what this signal needs.
- Count it out loud. "One-thousand-one" through "one-thousand-five" lands in the middle of the 4–6 second window. Release, then give a quick tap of about one second. Keep the gap short. The rule allows no more than three seconds between the two blasts.
- Point the trumpets at the bridge house, not your crew. Rotate the bell away from the people aboard. A train horn at arm's length is a hearing hazard. Our hearing safety and safe-distance guide explains why.
- Listen for the reply before you move. The tender has up to 30 seconds to answer. If you hear nothing, repeat the signal. The rule says you keep signaling until you are acknowledged.
- Practice at the dock with the remote, if you plan to use one. A remote is handy when the horn is mounted on a rail or T-top. Before you rely on it at a bridge, check that you can hold a five-second blast and then give a clean one-second tap with it.
If you want a horn that stays mounted, see our pontoon rail-mounting guide and our T-top and tower mounting guide. Both let you sound the signal hands-free while you hold the boat in position.
Radio First, Horn as Backup (In Most Places)
In practice, many skippers call the bridge on VHF before they ever touch the horn. The rule permits it: under 117.15(d), radiotelephones may carry the same information as the sound and visual signals. Boating Magazine notes that most bridges monitor channels 13 and 16, while Florida bridges monitor channel 9. Coast Guard rules for individual Florida bridges back that up. A 2023 Federal Register rule for an Okeechobee Waterway bridge at Stuart, FL, for example, says the tender will monitor VHF-FM channels 9 and 16.
Once you make radio contact, the rule requires both you and the tender to stay on that channel until you have cleared the draw. The horn still matters, though. The same section says that when radio contact cannot be established or kept, you must use the sound or visual signals. Dead handheld, a busy channel, a tender who doesn't answer: in each case the horn is how you ask. That's why it pays to keep a horn aboard that is loud enough to cut through.
When You Must Not Signal (and When the Bridge Won't Open)
A loud horn makes it tempting to signal every bridge you pass. Don't. 33 CFR 117.11 prohibits signaling a drawbridge to open in two cases. The first is when your boat would clear the closed span once any lowerable, non-essential gear is lowered: antennas, outriggers, a folding T-top. The second is any purpose other than passing through. That means no honking at the tender for fun, and no blasting the bridge as a greeting. Violations are handled by the Coast Guard District Commander under 33 CFR 117.49.
Before you signal, know your boat's air draft and read the clearance gauge. Under 33 CFR 117.47, clearance gauges are required at drawbridges on waters that drain into the Atlantic south of Delaware Bay or into the Gulf. Then check the bridge's own schedule. The general rule in 33 CFR 117.5 is that a drawbridge opens promptly on signal. Individual bridges, however, carry exceptions in Subpart B. On Florida's Atlantic Intracoastal Waterway, for instance, the Bridge of Lions in St. Augustine opens only on the hour and half-hour from 7 a.m. to 6 p.m. Weekdays it skips the 8 a.m., noon and 5 p.m. openings, except on federal holidays (33 CFR 117.261). Each bridge must post its schedule on signs upstream and downstream, so you can read it as you approach.
The 5-short-blast request during a closure period is not a workaround for impatient boaters. Under the regulation, it is only for vessels that must be passed through during a scheduled closure. The Florida section, for example, lists public vessels of the United States and tugs with tows. Everyone else waits for the next scheduled opening.
Which Horn Works Best on the Water
Any of our horns produces a legal drawbridge signal. The choice comes down to how much else you use it for. If the bridge request is the main job, a dual-trumpet model is plenty. If the same horn also serves as your fog and passing signal on a larger boat, or you run long open stretches where wind eats sound, more output helps. For a full rundown, see our best train horns for boats guide.
At the top of the range, the Extreme Series Train Horn for Milwaukee® 18v Battery is rated at 150 dB. It runs on any Milwaukee® M18™ battery and comes with a wireless remote with 160 ft range, which you can upgrade to the 2,000 ft Long-range Remote. Because it uses the same pack as your tools, a spare charged battery in the console is your backup. No air tank to fill and no wiring to corrode.
The horn is not just for bridges. Committee boats use the same tool to run start sequences, which we cover in our sailboat race start horn sequence guide. If you also use your horn on the road, the best train horns for trucks roundup compares the full lineup.
FAQ
What is the horn signal to open a drawbridge?
One prolonged blast of four to six seconds, followed within three seconds by one short blast of about one second, per 33 CFR 117.15(b)(3). Repeat it until the tender acknowledges.
What do five short blasts from the bridge mean?
The draw can't open right away, or it is open and about to close. Stop, hold well clear of the span, and wait. The tender keeps repeating the signal until you acknowledge it.
Is a battery train horn too loud for a drawbridge?
The regulation only asks that the signal be loud enough for the drawtender to hear. It has no maximum. Point the trumpets toward the bridge house and away from your crew, and sound only the required blasts.
Can I signal a bridge just to watch it open?
No. 33 CFR 117.11 prohibits signaling for any purpose other than passing through, or when your boat would clear the closed span once lowerable gear is down.