What Are Boat Locks?

Boat locks are the infrastructure that lifts a boat from a lower body of water to a higher body of water without ever removing it from the water. Even if they're called "boat" locks, they might move a vessel more than 1,000 feet in length, like the boat locks at Sault Ste. Marie, Michigan, that raise and lower ships (regardless of their size, on the Great Lakes, they're called "boats") between Lake Superior and the other Great Lakes.

Function

Boat locks act like an escalator for boats and ships, moving the vessel vertically to avoid abrupt changes in the water level. They're used at places where waterfalls or rapids might have existed, or where waterways take another sudden plunge owing to a change in the elevation of the land surface as a river moves toward the ocean. Without the locks at these places, most boat travel would be impossible.

History

Locks have been in use for over 1,000 years. They were pioneered by the Chinese in the 10th Century A.D. and re-invented by the Dutch in about 1240 A.D. Although materials and construction methods have changed, the principle of operation remains the same: water seeks its own level and, if allowed to do so in a confined space (like a lock chamber) you only have to open a valve to drain higher water into the lower chamber from one of the chambers--or the river--above, by the force of gravity. Pumps are not required. Locks eventually appeared where needed throughout England and continental Europe, in Russia and in Asia. Some of the earliest locks in North America were those on the Erie Canal in the State of New York.

Significance

Water transportation has always been more economical than overland transportation, usually because of the quantities of goods that could be carried with a minimum of infrastructure--no highways to be built, no railroad tracks to lay, and a small crew that handled both the boats and the unloading of freight. This economy of effort persists even today, and locks are a significant factor in making otherwise impassable waterways functional--the Sault Ste. Marie Locks in the Great Lakes are one of the largest of the 191 active locks in the United States--including the familiar locks on the Panama Canal used to move ships in a 13-hour journey between the Atlantic and Pacific Oceans.

Locking Through

Recreational boaters should make themselves aware of the presence and location of any lock they might pass through during their travels long before they arrive at the "'fore bay" (the waiting area before the first chamber) of the lock. Most locks are listed in telephone directories under "U. S. Army Corps of Engineers." Passing through a lock requires the use of marine radio; a vessel entering the 'fore bay without radio contact is viewed with suspicion. While in the lock chamber, vessels are expected to be secured to the walls of the lock by ropes; the ropes should have sufficient slack in them to allow for the rise of the water level. All locks are equipped with light and sound signals to communicate when vessels may untie and exit a lock chamber. Vessels that fail to follow instructions may be cited by the lock master.

Physical Operation of A Boat Lock

In a two-chamber lock, the operation goes like this: when a vessel enters the first lock chamber, the chamber doors are closed, leaving the vessel floating in a temporary lake. The water from the second chamber is then discharged into the first chamber, raising the water level of the first chamber and lowering the water level of the second chamber. Then the doors to the second chamber open and the vessel enters the second chamber. When the vessel is secured in the second chamber, the second chamber is flooded from the river, raising the boat to the level of the river. The doors to the lock chamber open and the boat continues on its way.

Resources

• U. S. Army Corps of Engineers Lock Use Data