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What Are Canal Locks And How Do They Work?

Chris Riley by Chris Riley Updated on December 21, 2021. In nauticalknowhow

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If you’re an avid boater who likes to sail far and wide, channel locks are something you’re bound to encounter. If you stay in your own little lake or just off the coast you may never come across one of these interesting features. But if and when you do stumble upon one, you definitely need to know what it is and what it does. And also what you’re expected to do when you sail into one. So let’s take a look at canal locks and how they work.

What is a Canal Lock?

In the simplest of terms, a canal lock is a section of river or other navigable waterway that separates two other sections of different depths. You can think of a lock almost like an elevator on the water. You enter from one side and the water level is either increased or decreased until it is level with the water on the other side. It can raise and lower boats with a change in water supply thanks to gates at each end.

One example you may be familiar with in the US is the St. Lucie Lock. It’s one of five locks in a series you’ll find in the state of Florida. It allows boaters to traverse the Okeechobee Waterway from Stuart to Ft. Myers.

If you’re heading east, two locks will raise you up until you reach the water level of Lake Okeechobee. If you want to keep heading towards the sea, three more locks beyond the lake will lower you back down again by the time you reach Ft. Myers.

The Creation of the Canal Lock

A canal lock is actually far older than most people might think. Once upon a time, travelling by water was the easiest and fastest way to traverse the world, don’t forget. Especially if you were shipping goods. But our ancestors realized something fairly quickly – not every river can handle every boat. In fact, many bodies of water often prove to be too shallow for practical transportation. If you want to ship large quantities of goods, or even a boat with a large amount of people, what do you do?

Luckily, mankind is nothing if not industrious. When faced with rivers that were too shallow but a pressing need to make use of those same rivers, we adapted. The solution was to change the river and make it deeper.

The construction of dams dates back to at least 3000 BC. We developed this technology for a variety of reasons. Dams are able to redirect water flow in order to prevent flooding. They can also aid in bringing water to areas where there was no water before. This has benefits for irrigation and farming and then later for the creation of hydropower. And the other important reason for creating dams is navigation.

Ancient people realized they could dam a shallow river and force the level to rise. Eventually it rose high enough that the water would spill over. This spill is called a weir. The area behind the dam would be deep enough for boats to navigate. The process could be repeated down a river, essentially making it a series of steps from dam to dam.

There was another reason why locks came into play and actually became very common place. Once humans realized they could alter the flow of rivers that opened up a world of possibility. You could direct a river anywhere you wanted it to go. But geography didn’t always play nice. Many times the landscape would make it difficult, especially with things like hills. Locks were an efficient way to navigate around these.

Basically, a lock had to be used any place the land contours changed. That meant there wasn’t a lot of consistency in how locks were placed. It wasn’t as though early engineers were placing them every 1000 meters or anything like that.

The first step in navigating a shallow river was in place. A boat could enter and safely sail to the dam with no worries. But the problem at that point was how to get from the top step to the second step, which was below the dam at a different level? This is where locks come in.

The Creation of the Flash Lock

Like the name implies, a flash lock was meant to be a quick transition. Originally, when sailors needed to get a boat through a dam a flash lock was used. This was literally a passage right through the dam itself. It worked a bit like just opening a door in the dam. The boat could pass through, but obviously a rush of water did as well.

Heading downstream this could be precarious. A boat that may have been in a gentle current would be pushed through an extremely fast moving one all of a sudden. That could lead to serious problems.

Flash locks were developed in Ancient China and while they did work, they didn’t always work well. The sudden torrent of water could capsize or damage a boat. Many suffered serious damage and even sunk as a result.

Closing a flash lock involved moving something called paddles which were basically just panels of wood. They were arranged to form a wall that held the water back. Different lengths of wood called rymers held them in place. So when a boat needed to pass, workers would need to remove the rymers and lift the paddles to let a boat through. Depending on the body of water, this could be both a dangerous and time consuming job. In some locations, it would take more than a day for water levels to rise up to the normal levels after opening the lock for just one boat.

The other big problem with this design is what happens to a boat going the other way? Downstream at least has physics on its side. But boats heading upstream faced a much more laborious journey. Those boats, going from lower water level to higher water level. Needed a lot of work. Typically these were attached to lines and winches. The flash lock would be opened and the boat had to be hauled through, against the rushing current, to the higher level. You can imagine how much time and effort this would have taken. And how dangerous it could have been. Obviously a better method was needed, but the basic principle was sound. There needed to be a transition between the different levels. The pound lock was the answer.

What is a Pound Lock?

The word pound has a few meanings in English. You might think of beating on something, like pounding out a ball of dough when you’re making bread. And there’s the unit of weight we’re all familiar with as well. And yet a third meaning is the pound where stray dogs might be kept. And that meaning is shared with this kind of lock. A pound is a lock that has gates at two ends to control the water flow. When a boat is between those gates, it’s in the pound where it has to wait.

The idea of a pound lock is to make the transition between water levels easier. So a boat enters the pound lock through gate one and that gate closes. The water level on both sides of the gate is even, so there’s nothing to worry about right now.

The next gate can then open and drain the water out of the pound lock. The level goes down until it’s even with the level on the far side. The boat, not once again at an even water level, can sail out of the lock and continue on its way. That pound in the center means less potential stress and damage. It’s like having a mudroom in your house. Instead of just walking in from outside and making a mess everywhere, there’s a little transition in between where you can take your shoes off and shift from outside to inside.

History of Pound Locks

The pound lock was devised in China as well. A naval engineer named Qiao Weiyue came up with the concept in the year 984. The basics of the technology are the same as the ones we use today, over 1000 years later. So clearly it was a sound and solid idea.

They used hanging gates in these locks that allowed the water level to change slowly once they were closed with a boat inside. Kee[ in mind, this was no drastic change. Water levels only rose or fell by about 4 or 5 feet in each lock. That meant a number of locks had to be used as a boat travelled down or upstream, just like today. China’s Grand Canal Locks, the longest canal in the world, uses locks like these. As a result, they managed to raise the level of the canal 138 feet in total.

Throughout the 1300s and 1400s more elaborate pound locks were used in Europe. They became less prominent over the years as more advanced methods of constructing waterways were developed. However, they are still commonplace in longer waterways that allow for navigation from bodies of water of varying depths.

The Mitre Lock

The way the locks are designed has changed significantly over the years, but even the modern version has ancient roots. The original ones, as we said, were those wooden ground paddles. These were usable but hardly efficient. The seal they produced was by no means waterproof.

Later lock gates were a lot like those portcullis doors you see on old castles. They went up and down. This made for a more efficient barrier against the water than the paddle version, But that doesn’t mean it was the best by any means. Imagine lowering a single panel into a river that has a current pushing it. Unless the gate was not only very well made but securely lowered precisely into place every time, it was not a watertight chamber.

Mitre gates were developed by Leonardo da Vinci 1497. This lock works by having a pair of gates that open in unison and close in on each other at a 45 degree angle. This design is ingenious for use in the water. The pressure of the water actually forces the gate to close more tightly, rather than force it open like it does with other designs. Then, when the levels are even the pressure is equalized so opening them is simple.

Modern Locks

Technology has allowed for newer and better versions of older gates. Steel gates that lock in place can be implemented in modern locks. These are strong and effective. Caisson gates are like floating boxes that can block the passage of water. Swinging steel gates and even wooden ones are still used. Single gates can be used in a narrow lock while double ones are more typical in larger canals. There are rotating gates as well that rotate in and out of cylinders to open and close wider or narrow locks. The design may depend on the geographical needs and demands of the area.

Since adjusting to topography is no longer the chief concern with lock placement, their construction is more intentional these days. That means that locks are usually placed more evenly than they were in the past. No longer will a boat have to travel for miles and miles before wandering across a random lock. Modern technology lets us keep things a little more even and tight. This consistency makes it easier to manage traffic through locks. It also makes the job of monitoring them more simple. And, when their construction is more purposeful, it means any maintenance and repair is easier as well.

What is a Lock Keeper?

In ancient times, a lock could not operate as an untended feature. Someone needs to be responsible for lock operation to ensure it is opened and closed safely and properly. This person is known as a lock keeper. Sometimes they’re also called operators or tenders.

Modern locks still have lock keepers but the technology has been greatly upgraded to make their jobs easier. Back in the day, being a lock keeper was more than a job, it was basically that person’s life. They didn’t wake up and head to the lock in the morning, they lived there. Like lighthouses and lighthouse keepers, lock keepers had to be there all the time in case they were needed. There are even modern museums built in the homes of former lock keepers.

The chief duties of a lock keeper are to operate the lock and assist boats travelling up and down river. This is a job that requires 24 hour a day monitoring so it can be a lot more intense and stressful than you might think.

Historically, lock keepers had to maintain water levels in addition to their duties helping boats pass through. During rainy seasons they needed to monitor levels to prevent flooding. And during droughts they might have to allow more water to pass to maintain levels. Other duties might include checking waybills and paperwork to ensure boats passing through have authorization to do what they’re doing.

Thanks to technology, a lock keeper at a lock today doesn’t need to be physically on site at every lock. This makes it easier for canals where there may be 5 locks in a row. The lock keeper can work at a central control room and operate every single lock in order. They can monitor water levels and weather and use cameras to keep an eye on the area without leaving. It saves time and centralizes the process. One lock keeper is better able to understand the needs of a boat going through than five different keepers.

Lock keepers can now see boats coming and prepare in advance. They can control the flow of traffic and accommodate multiple boats in a row easily and efficiently.

Some of these control centers will control much more than locks as well, including any other technological features on a waterway. In the Netherlands, one control center operates 18 different locks and 28 bridges.

One thing to be aware of, especially if you’re boating internationally, is that not every lock is manned. And that means there’s not a control center either. Some locks are entirely up to you to manage as a boater. In this case you’d bring your boat up to the lock landing and tie it off. Then you get off your boat and head to the lock controls. These are typically just gates that swing open and closed. So you just need to use a little elbow grease and push the lock open. Then you head back to your boat, untie it hop on board and proceed into the lock chamber you just open. Naturally, this is where you tie off again, get off the boat, and close the gate behind you. You may need to climb a ladder if you’re intending to raise the water level rather than lower it.

This is where you secure the boat with ropes again and then start to open the next gate. If you’re doing this along, you’ll really need to be careful manning those ropes to hold your boat steady. Essentially you have to be a minor league lock keeper for a few minutes until you get things the way they need to be. Remember to close the gates properly after you’re doing so the next boater has an easy time of it as well.

Lock Flights

That control center in the Netherlands certainly operates a lot. But it’s still not the biggest group of locks in one place at one time. When locks are organized in large groups they’re called lock flights.

Lock flights are used when a serious change in water depth needs to be achieved from the start of the flight to the end. It would not be possible to have a single lock change the water level 150 feet by any means. That would be impractical, time consuming and dangerous if there was even a way to make it work. So the change needs to be done gradually from one lock to another. But the change can be very significant.

A series of 30 locks are used at Caen Hill Locks on the Kennet and Avon Canal in England. The water from one flows down to the next so no more water is used than a single lock would make use of. And it’s large enough to accommodate boats going in both directions. In fact, the way it’s organized is so efficient that boats can go up and down at the same time.

How a Lock Works: The Basics

If you’re unclear on how exactly a lock is able to change water levels, don’t worry. Let’s take a look at the process in a basic way so you can understand exactly what’s going on.

  • When a boat approaches a lock, the bottom sluices will be opened. This allows the lock to drain out until the water level is where it needs to be.
  • Once drained, the lower gates are opened up. A boat can now enter the lock as the water levels are going to be even at this point.
  • Once the bottom is in the lock, the lower gate is closed behind it and the sluices are closed as well. This will allow the water level to start rising again.
  • The top sluices are opened up now. The water level can begin to rise as it fills in between the two gates. The boat just needs to sit in place and let the water rise beneath it.
  • Once the water level has risen to be even with the higher level, the upper gate can open. The boat is free to head along the river at the higher elevation.
  • When approaching from the other side, the exact same process occurs just in reverse.

What is a Sluice?

So in our description we talk about water coming in through a sluice, which we never mentioned before. What is a sluice? A sluice or sluice gate is basically just a smaller and more easily controlled version of the gate itself. These can be raised and lowered to allow water through

How Do Locks Work in a Tight Space?

We mentioned earlier that dams were used to create a staircase design. This is still prevalent today with some locks if there are space concerns. In theory, there doesn’t need to be a large space in between locks, just enough room to safely hold a single boat, right? So there are places where staircase locks are used to go from a higher to lower elevation fairly quickly.

Along the Canal du Midi in France you’ll find the Seven locks of Béziers, or the Fonseranes Locks. This is a staircase lock and it’s used because it’s both efficient and cheaper. The difference between a staircase lock and a series of locks in sequence like a lock flight is how the gates are arranged. A staircase lock only has one lock between chambers. So the bottom gate of one chamber is the top gate of the next. A flight would have these separated so each chamber has its own top and bottom gate.

These locks raise a boat 71 feet over a distance of 980 feet.

Staircase locks are a little harder to navigate than traditional locks. Because they’re so close together and operate a steep incline, things need to be conducted more tightly. It’s possible to flood the downpath if too much water is let out too soon. In order to minimize problems these locks are often either completely filled in all pounds or completely emptied with the exception of the first one that the boat will enter. Then the water level can be raised or lowered as needed from that point, rather than raising or lowering each one individually as the boat proceeds.

Pairing Locks

In a highly trafficked canal, it may make more sense to have several locks side by side. You can find these in the Panama Canal, for instance. There are actually three different sets of double locks along the Panama Canal. Because of the extra locks, traffic is able to flow more smoothly along the canal. This is especially important during very high traffic times of day. Upwards of 40 vessels travel the Panama Canal on any given day which is just shy of 15,000 per year. That’s a lot of traffic so you can see why it makes sense to have these additional locks to accommodate them on their way.

Navigating a Canal Lock

Knowing the history of locks is one thing, but what happens when you approach one as a boater? How do canal locks work practically? There is a process that should be followed. If you know you’re going to be dealing with one for the first time, it’s good to familiarize yourself with the rules and customs of navigating through locks.

The first thing you need to do when approaching a lock is to get in touch with the lock keeper. You’ll need to coordinate your run through the lock and that means talking to each other. Your VHF radio is key for this but there is no standard channel that lock keepers monitor. As you approach a lock, keep your eyes open for signage. The VHF channel you need to access should be clearly posted. Likely it will also be posted more than once just in case you miss it. Once you know how to get in touch, do so and listen to the lock keepers

 

instructions.

Modern locks have traffic signals to help make navigation easier and safer. But you do need to pay attention to them for this to work. Approach any lock with caution at a reduced speed. The signals will let you know if you’re safe to proceed or if you need to hold your position. Remember, there could be boats ahead of you waiting and including in the lock itself. So the process could take some time and you may need to sit and wait for a while. It all depends.

When you’re preparing to enter you need to set up your fenders. Rig fenders on both sides of the boat and then get lines ready. Prepare a bow line and a stern line. Odds are the lock already has lines prepared where your boat will need to be tied up but it never hurts to be prepared.

The traffic signals are the simple ones we’re used to. Red light means stop, green light means go. The lock keeper will be in touch on the radio, but the signals are also very clear. When the lock is clear the light will turn green so you know you’re ready to enter.

Upon entering the lock you’ll be instructed on where to go. If the lock is manned a lock keeper may help you with the lines at this point. You’ll have a bow line and a stern line. These can secure you in place and will keep you front drifting about as the sluices leave you with a full or empty lock.

Many locks are large enough to accommodate several vessels. This is another reason why it’s important to tie the boat in place. You don’t want to be drifting into another vessel in a lock. There’s no room to maneuver very much in a lock and you don’t need to be hitting someone else.

If there’s a lockmaster, be careful as they toss you the lines. Make sure you’re paying attention so you don’t get hit in the face. It sounds silly now but if you’ve ever been hit in the head with a bow line from up above, it’s not all that comfortable.

Wrap the lines around a cleat at the bow and the stern of the vessel. If you have the crew on board, get someone to monitor each one just in case. Turn the engine of your boat off and just let the lock do its own work now. You can turn on your radar at this point as well, if you have one.

Once you are secure, that is when the lock gate will be closed behind you. The sluice or gate in front of you will then be opened after that to allow for the change in water levels. This is an important time for you and the crew to monitor the boat. As the water level raises or lowers, depending on where you’re going, you need to watch the lines. Whoever is manning the lines at the bow and the stern needs to pay attention. They’ll need to take up slack or let it out in order to keep the boat stable and in place.

As the water levels rise or fall, your fenders will likely get a workout. The current created by the flow will probably scrape you against the walls of the lock. As long as your fenders are secure, that will hopefully not be a big deal and will not damage your boat.

The amount of time it takes to navigate a lock depends on where you are. Some locks don’t have as much of a depth difference between sides as others. For instance, the lock at St. Lucie shifts the water level about 15 feet in total. The wait is just several minutes long so it won’t be a great inconvenience to your journey overall.

Once the levels are even, the gate will open. This is when you should restart the engine of your boat. Do this before undoing the lines and tossing them back to the lock master. Once your boat is untethered, check with the lock keeper again on how to proceed. They’ll direct you on when and how fast you can exit the lock.

When it comes time to leave the lock, make sure you’re being careful. There could be boats on the other side waiting to come in. The lock keeper will probably alert you to this, but not always. So just remember to take it slow and be observant,

Once you’ve left the gate and gone past any waiting vessels, go ahead and pull your fenders back in. You’re good to continue on your journey. Depending on the body of water you’re travelling you may have to go through this several times, of course.

About Chris

Outdoors, I’m in my element, especially in the water. I know the importance of being geared up for anything. I do the deep digital dive, researching gear, boats and knowhow and love keeping my readership at the helm of their passions.

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