“Can I fit my boat under that bridge??!!”
This is a frequently asked question among boaters, especially around the Boston Harbor area. Like many urban areas, the Boston Harbor area contains many canals, rivers and waterways through dense urban or thickly settled areas. These passages are most often navigable but can pose challenges and the ability to get through may be subject to the tide. There are at least four different types to be found in Boston Harbor and along the Massachusetts Bay coastline: Fixed, lift, swing, and bascule. (A bascule bridge is a fancy name for a drawbridge). Fixed bridges are the most straightforward, as they are usually high enough for shipping traffic to fit through at all tides. The other three, which all have an opening function, often require a radio call to an operator, or adherence to an opening schedule.It is a little known fact that the helpful folks over at the NOAA include updated bridge height data right on nautical charts. It is usually marked close by to the actual location of the structure in small type. The text will usually describe the type of bridge (as discussed below), the vertical clearance and the horizontal clearance. Charted clearance levels are reported at mean high water level (meaning essentially high tide, more detail about this can be viewed here).
Here are examples of the different types of bridges found around the Boston Area:
The Fort Point Channel, has both a swing bridge, with seven feet of clearance when closed, and a fixed bridge with 16 feet of clearance, as seen on the chart* below:
The swing bridge opens with a wave or radio call to the operator. Below is a photo taken as it opens:
Further south, the Fore River is spanned by a lift bridge. This is usually the type of structure seen when heavy traffic must cross a busy waterway accommodating large ships. It is also often used for rail bridges given the weight of trains. The Fore River overpass is part of busy Route 3A, so an opening is a relatively rare occurrence which requires advanced notice. Given that it has 54 feet of clearance when closed, only very large vessels would require an opening. Here is chart* of this lift structure spanning the Fore River below:
The Fore River’s lift bridge:
The large fixed structures over the Cape Cod Canal, the Bourne and the Sagamore, are good examples of fixed bridges, although the canal is also crossed by a lift bridge for the railroad. Below is the labeling of the Sagamore bridge on a Cape Cod Canal chart*:
A view of the Cape Cod Canal looking South from a high point on the Sagamore. Further down the canal in the distance, one can see the railroad bridge, which is a lift structure:
Finally, a “bascule” or draw bridge. There are two of these crossing the Annisquam River in Cape Ann. The picture at the top of the post is of the Blynman Bridge, which opens by radio call and can be seen in the chart* below:
The Annisquam River in fact has TWO bascule bridges! The bridge at Blynman Canal (which is pictured at the top of this post), and the rail bridge supporting the Rockport commuter rail line, seen below:
The McArdle Bridge in Chelsea, another bascule bridge:
This is only a very partial summary of the bridges that will be encountered in the Boston area. Other well known bridges in the area cross all the major rivers, including the Mystic, the Neponset, and the Charles (where locks add another level to the complexity). further out in Massachusetts Bay, boaters will also encounter bridges in Salem Harbor, the North River, and the Merrimack River.