The expression “boat lift” suggests a crane or other facility for lifting boats in a shipyard, but this is about an alternative to locks on a canal or river to allow boats to move from a higher to
a lower level, or the reverse, of course.
Normally, a lock or a series of locks is the simplest construction for doing this. The boat—actually, we are talking about transport vessels that can be 100 m long—enters the lock basin, and the lock doors are closed behind it. To raise the boat, water from upstream is allowed to flow in the basin. To lower the boat, the water is released downstream. When the level of the water in the basin is the same as that in the river or canal in the direction the boat is heading, the lock doors are opened. Elementary.
One disadvantage of this, especially in canals, is the constant loss of water, especially if the terrain requires several locks for the canal to descend from a plateau before continuing at a lower level. The time required to transverse several locks is also a drawback, as is the effort and expense of operating and maintaining several locks.
In some places, a canal ends at a river whose level is much lower. This is the situation near Eberswalde in Germany, where the canal from the Havel river ends 36 m (188 ft) above the Oder river. Originally, there was a flight of four locks to let boats descend, but they could not handle the traffic in both directions.
In the early 1930s, a boat lift was constructed. The boats are not lifted out of the water. The lift has a big basin that can be raised and lowered on 256 cables (half of them a little slack as a safety backup). The boat enters the basin from the river, and the doors are closed. At the level of the canal, two sets of doors are opened: one set for the basin, the other set, which was keeping the canal from draining.
The beauty of the system is that the weight of the basin is always the same, either just full of water, or with a boat, which displaces its own weight of water. The basin can thus be perfectly counterbalanced, all those cables running over 12 ft rollers to counterweights. The only energy required is to set the whole thing in motion.
The concept of the boat lift was developed and implemented in the late 18th century, the heyday of canal construction. The most modern and elegant boat lift is the Falkirk Wheel, the world’s only rotating boat lift. The basic principle is the same, but the counterbalance is a second basin, so that one boat can be raised while (in theory) another one is being lowered. The practical efficiency with the two basins is that a following boat can immediately enter the second basin, without the lift’s having to return to its original position. Whether the traffic between the canals justifies this aspect is a moot point.
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