How to Boat Safely Under Bridges of All Types

January 12, 2026

It may seem simple at first, but navigating safely under bridges actually requires some knowledge and preparation. You’ll need to understand the height of your boat, the bridge clearance, the movement of the tides, marine communication procedures and right-of-way rules. A bit of boating etiquette goes a long way too!

Keep reading to discover what you need to know to boat safely under bridges of various types in the United States.

Key Takeaways

To safely navigate under a bridge, you need to understand and apply your knowledge of the following: your vessel’s air draft; the horizontal and vertical clearance of the bridge; the tide level; the bridge name; the VHF channels used to communicate with the bridge tender (if there is one); speed limits, and right-of-way rules.
While you may need specific skills or knowledge depending on the type of bridge involved (fixed, swing, lift or drawbridges), general rules of boating etiquette, respect for boating safety regulations and staying alert are always important.

What you need to know to safely navigate under a bridge

To safely navigate under a bridge, you need some specific information at your fingertips:

Air draft

Know your air draft, which is the distance from the waterline to the absolute highest point on your boat (including antennas, masthead lights, or outriggers).

Nautical charts and clearance guides

Nautical charts list two types of clearance: Horizontal (width) and Vertical (height). This information will help you decide whether you can safely fit your boat under a given bridge, by showing the clearance measured from a specific chart datum (like Mean Higher High Water, or MHHW).

You can also download a copy of the USCG Clearance Guide, which lists bridge clearance in many parts of the country.

Tides

If you are navigating coastal waters, you also need to know the current water level, which can change with the tides. This means you need to check tide tables and adjust for real-time conditions. During low tide, you gain clearance; during high tide or storm surges, you lose it.

The Coast Pilot

You should also have a copy of the United States Coast Pilot for your area (available for free online from the NOAA). It provides specific details on bridges and bridge opening schedules, which can change seasonally or at specific times of day.

What to Look for When Approaching a Bridge

As you approach a bridge, look for these key visual cues:

The Clearance Board (or Tide Gauge)

Located on the right-hand side (fender system) of the bridge opening. This is a large vertical ruler that shows the actual clearance in feet from the water level to the lowest part of the bridge structure at that exact moment.

Additional Signs

Bridges are often “No Wake” zones and usually also have specific speed limits. Be extra careful.

You’ll also need the following to contact the bridge tender and request that the bridge be opened:

The bridge’s name and hours of operation, shown on a white sign.
The VHF channels the tender monitors (usually 13, 16, or 9) shown on a blue sign with a telephone/lightning bolt symbol.

Navigating Under Specific Types of Bridges

While every bridge serves the same purpose, their designs present different challenges to recreational boaters. Understanding these differences is the first step toward a safe transit.

1. Fixed Bridges

Fixed bridges are permanent structures that do not move. Your safety depends entirely on your math and the tide.

Tip

If you think it’s close, it’s too close. Even if your mast clears, the “suction” or “squat” created by a boat moving at speed can pull the stern down and lift the bow, or wake from another vessel can toss your mast into the girders.

2. Drawbridges (Bascules)

Bascule bridges use counterweights to pivot upward. Remember that as a bascule bridge opens, the clearance increases the further you are from the hinge.

Tip

Aim for the center, but be aware of the “leaf” (the part that moves) hanging over the water. When waiting for an opening, stay well back to give yourself room to maneuver against wind and current.

3. Swing Bridges

Swing bridges rotate on a central pier, creating two narrow channels on either side. Usually, only one side of a swing bridge is designated for deeper drafts.

Tip

Check your charts and look for navigation markers. Avoid getting too close to the bridge walls, as currents can pin you there while the bridge is in motion.

4. Lift Bridges

These bridges have a center span that rises vertically while remaining horizontal. It can be difficult to judge how high a lift bridge has actually risen.

Tip

Wait for the bridge tender to give you the “all clear” or until the span has reached its full height before beginning your approach.

Requesting an Opening

What’s the best way to ask for a bridge to open? There are a few options:

VHF Contact

This is the preferred method. Call the bridge by name: “Bridge Name, Bridge Name, this is the Sailing Vessel [Name], northbound, requesting an opening.”

Sound Signals

If your radio fails, use your horn. One prolonged blast (4–6 seconds) followed by one short blast (1 second). The tender will reply with the same signal if they are opening.

Know your navigation sound signals. If the tender sounds five short blasts, it means No or Stop. Do not approach. You must acknowledge this by blowing five short blasts back.

Passing Under a Bridge at Night

If you are boating at night, look for three red lights in a triangle. The two bottom lights mark the edges of the channel and the top light marks the center of the span. Keep the top light centered between your bow rails.

Important

Did you know that it is a federal offense to cause an “unnecessary” bridge opening? According to U.S. Coast Guard Bridge Programs, you must lower any elements of your vessel that can be easily moved, (such as VHF antennas, outriggers, or Bimini tops), if doing so will allow you to pass without an opening.
Be polite! Bridge tenders are federal or state employees. Avoid “demanding” an opening. Ask for the next scheduled opening or state your position clearly. A “Thank you, Captain” after passing goes a long way.

Treat Every Bridge with Caution

Even if you have 20 feet of clearance, approach carefully.

Bridges are visual obstructions. Always slow to idle speed. A boat coming from the other side may be hidden behind a pylon and dart out just as you enter the narrowest point. Be prepared to respond correctly according to right-of-way rules to avoid a collision.

Generally, the vessel with the following current has the right-of-way, as they have less maneuverability. However, common sense dictates that the first boat to arrive is often the first to go through. Keep an eye on other waiting vessels to avoid a jam once the gates go up.

Checklist for a Safe Passage Under a Bridge

Know your height (air draft).
Check the tide gauge on the bridge fender.
Lower what you can (antennas, etc.).
Communicate clearly on VHF 13 or 16 (or the channel indicated).
Read all signs.
Follow all instructions (sound or verbal) from the tender.
Slow to idle and stay centered as you pass under, staying prepared to follow right-of-way rules at all times.

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