Approach bridges slowly and cautiously, making sure your wake doesn’t create problems for other boats.
Many inland lakes and rivers have no minimum bridge height. Maps and charts show the center channel span with its horizontal and vertical clearances.
To be sure your boat will safely clear the bridge, refer to the clearance gauge affixed to the bridge’s right side upon approach. The gauge marks the distance between the bridge channel span and the waterline, not the water depth under the bridge.
At night, a green light marks the center of the navigable channel under a bridge, and red lights mark supporting piers. Stay clear of the piers as you may be unable to see protective framework until it’s too late. Strong currents, exposed rock and trapped debris can also be present.
To determine a drawbridge’s clearance, contact the bridgetender on VHF Channel 13 or 16 (Channel 9 in Florida, Georgia or South Carolina) using the low power (1 watt) setting.
Never ask for an opening if your boat will fit under a closed bridge. You must lower radio antennas or movable masts if necessary.
If you can’t talk to the bridgetender on VHF, you can request an opening with one long (4–6 second) and one short (1 second) blast. The bridgetender will return the signal if the bridge can be opened immediately. If the bridge cannot open or is closing, the tender will sound the danger signal—five short blasts.
Not all lift bridges open on demand or on a set schedule. Railroad drawbridges can stay down for hours. Local knowledge is essential if you don’t want to get stuck between a drawbridge and a railroad bridge while waiting for the latter to open.
For more information on navigating inland waterways, take the Boating on Rivers, Locks and Lakes seminar at a squadron near you.