There's something remarkable about a boat travelling uphill. Canal locks are a simple yet ingenious system that has made it possible for centuries.

The humble lock gate has more to it than first appears. Here's how one of the most common types works.

For a boat approaching a lock from below and meeting a closed gate:

Close the top gate to seal the lock. Then, open the sluice (or paddle) in the lower gate — often a sliding panel — by cranking it with the ever-handy windlass (a simple metal crank that fits onto square spindles on the lock mechanism).

Once the water is at the lower level, you can push the giant counterweights to open the gate and steer the boat inside. Don't nudge too far forward, or you'll bump the cill, a stone ledge at the top end of the lock. Close the gate behind you and shut the sluice to stop water escaping.

With the lock sealed, open the top sluices. These often feed through side channels or culverts, letting water in gently from upstream, usually below the surface, to reduce turbulence. You'll gradually float upward as the lock fills.

Once the water level matches the upper pound (the upper stretch of water), open the top gates, close the sluices, and cruise on your way.

The same principles, in reverse, work for approaching the lock from above.

As you can imagine, operating locks is much harder work if you're boating solo.

One thing that makes all this possible is a steady supply of water. You can't rise in a lock without water to fill it. So, canal builders had to ensure the canal had enough water to stay navigable and to keep the locks functioning.

For some of the London canals, the builders created huge reservoirs with long feeder channels to ensure the canals had enough water. In some places, water is pumped back uphill to be reused at the top of a flight.

Canal water doesn't flow much — it's a closed system in many places. I'd heard that, in principle, it only takes one lock's worth of water for a boat to travel down a whole flight of locks: each lockful of water carries the boat one step down and ends up in the next pound. So, a boat going down several locks essentially transfers a single chamber's worth of water from the top to the bottom.

But in practice, how much water gets used depends on boat traffic from either side, whether you meet locks full or empty, and water-saving features such as side pools. In my research, it wasn't as simple as it seemed.

Holding back tonnes of water is no small task. Mitre gates are angled to meet, pointing upstream and forming a shallow V. This shape means the water pressure pushes the gates closed, creating a tight seal — the water effectively locks itself in.

A stone arch bridge uses a similar principle—compression strengthens the structure under pressure.

Leonardo da Vinci sketched an early design for the mitre gate around 1500. The design still looks like a modern lock gate. Not bad for an invention 500+ years ago.

Canal locks are like playing with water in the bath but on a massive scale. They're inherently satisfying to watch and operate. At their peak, they revolutionised transport across much of Europe and beyond.

The same basic idea still operates in the Panama Canal, where giant ships are lifted 26 metres over the isthmus simply by filling and draining the lock chambers in sequence.

The dimensions of a lock determine the size of the boat that can pass through. Panamax is the maximum size a ship can be to fit through the Panama Canal—a constraint that shapes shipbuilding worldwide.

In the UK, Tardebigge Locks has 30 locks to raise boats 67m over just 3.6km. Not to be outdone, Caen Hill Locks on the Kennet and Avon Canal has 29 Locks, 16 of which are in a straight line, rising 72m over 2.1km.

We recently took a canal boat trip on London's Regents Canal, including a visit to London's Canal Museum.

Far from its industrial heyday, the whole place was buzzing with people out for leisure up and down the length of the journey. The towpath—horses towed the barges by walking alongside—was packed with walkers, joggers and cyclists.

And it never failed to fascinate when the boats moved up or down a lock.

Naismith's Rule (including the term "lock miles")

Canal Locks

It’s always been mind-boggling to me how some of the largest and heaviest things we build on Earth are ships that float on water. Cruise ships are like floating towns, some able to accommodate over 5,000 people. How can it be that these gigantic, impossibly heavy objects made of steel can float on water? The key is displacement and realising the considerable weight that the water already supports.

In a lake or ocean, each drop of water is supported by the water around it. 1m³ of fresh water weighs 1 metric tonne, which is 1,000 kg. If a ship displaces 1m³ of water, the buoyant force of the surrounding water supports 1 tonne of the ship’s weight. Therefore, a ship weighing 50,000 tonnes will just float if it displaces 50,000m³ of water.

Sea water contains salt, which makes it denser than freshwater. As the denser water supports a greater weight, a ship will float slightly higher in salt water than in fresh. The International Load Line, previously called the Plimsoll line, shows how deep a boat sits in the water.

To realise the immense power of water, you can try submerging a biscuit tin in a bath. It’ll put up quite a fight.

Buoyancy

Point Nemo is the furthest point in the ocean from any land.

Imagine falling overboard and needing to swim to the nearest shore; the longest possible swim would start at Point Nemo. This puzzle, known as the Longest Swim Problem, finds its solution far into the South Pacific Ocean at Point Nemo.

Where is Point Nemo? (Location & Coordinates)

Point Nemo, officially known as the Oceanic Pole of Inaccessibility, sits at 48°52.6′S 123°23.6′W, over 2,688 km from the nearest land. It is the single most remote location on Earth, entirely surrounded by open ocean.

The furthest point from land is a point with a maximum equal distance to three points of land. If you moved in any direction from Point Nemo, you'd be closer to one of the points than the others.

The three nearest landmasses to Point Nemo, each about 2,688 km away, are:

Moto Nui, a small islet off the coast of Rapa Nui (Easter Island)

Maher Island, off the coast of Antarctica

If you've ever been somewhere with only the sea in all directions, imagine what it would feel like to begin a 2,688 km swim (!) from there.

Croatian survey engineer Hrvoje Lukatela identified and named Point Nemo using computer calculations. Lukatela named it after Captain Nemo from Jules Verne's classic story Twenty Thousand Leagues Under the Sea. Nemo means nobody in Latin.

Lukatela faced challenges in determining its exact coordinates, such as choosing the edge of Ducie Atoll's tidal sandbar and Maher Island being beneath ice for most of the year.

One of the strangest facts about Point Nemo is that it is a designated spacecraft cemetery. Since the 1970s, NASA, the European Space Agency, and others have deorbited satellites and spacecraft over this remote spot. The lack of human activity and extreme remoteness make it the perfect safe crash site for space debris.

Over 250 spacecraft, including the Mir space station, have ended their journeys here in this region. The International Space Station itself is also planned to end here when it is retired.

At any given time, likely the closest people to Point Nemo are often those in the International Space Station passing overhead a mere 400km above.

The waters surrounding Point Nemo are part of the South Pacific Gyre, a massive current system that isolates it from nutrient-rich waters. As a result, marine life here is scarce, making it one of the least biologically active parts of the ocean.

The Oceanic and Continental Poles of Inaccessibility

Point Nemo is also known as the Oceanic Pole of Inaccessibility. In contrast, the Continental Pole of Inaccessibility—the point on land furthest from the ocean—is in northwestern China near Kazakhstan, a remarkable 2,645 km from the nearest shore.

And the antipode to Point Nemo, the point directly opposite it on Earth's surface, lies somewhere in Kazakhstan.

Point Nemo has a lovely spread in Simon Kuestenmacher's book Marvellous Maps.

Writing about Point Nemo makes me want to rewatch Life of Pi and listen to the captivating music.

Point Nemo: The Most Remote Place on Earth and the Spacecraft Graveyard

The siphon, or syphon, is a simple device that uses only a tube to seemingly pump water from a higher spot to a lower one. It's ingenious because once you start the siphon by filling the pipe to below the height of the upper reservoir level, it will continue draining the water, pulling it over the hump and towards the collection below without further help.

Most of us use siphons several times daily, as there are often two at work in the standard toilet. Sometimes there's one in the flush mechanism—one push of the handle to start the siphon drains the water from the reservoir until it runs out. And you can flush a toilet using the second siphon by pouring enough water directly into the bowl to push the water over the bend in the pipe to start it— think how the water drains by itself almost completely before filling up to the level of the bend once again. It's a clever way to power a toilet flush with just the press of a button or turn of a handle. They also minimise leaks and control the flow by running the water uphill.

We set up a greywater siphon to drain water from the bath and showers to a water butt in the garden. To get it started, we connected the end of the hose in the garden to a tap and ran water back up the hose until it shot out the top. Then, dipping it in the water, turning off the tap, and putting the end in the water butt, like magic, the siphon pulls water out of the bath until it's empty.

Surprisingly, a few effects are at work in a siphon, and its mechanism is debated. They can be made to work in a vacuum and even spray liquid upwards with the right setup.

I read that it is from the ancient Greek siphōn meaning a tube or pipe, often for drawing wine from a cask—that would be a decent situation to start the siphon by sucking on the end.

Siphon

The two most commonly used temperature scales are Celsius and Fahrenheit. The Celsius scale, named after Swedish astronomer Anders Celsius, sets 0C at the freezing point of water and 100C as the boiling point of water at 1 atmosphere of pressure — normal air pressure at sea level. The Fahrenheit scale has 32F as the freezing point of water and 212F as the boiling point. With 180F between freezing and boiling that means each degree Celsius is 1.8 degrees Fahrenheit.

Several accounts of the creation of the Fahrenheit scale exist but the general gist is that Daniel Fahrenheit set 0F at the freezing point of a brine mixture, 32F at the freezing point of water, and another point at body temperature around 96F (now 98.6F). He divided up the scale between these points giving a scale with helpful resolution.

It's interesting to think that for most of history, there was no comparable way to say how hot or cold something was.

Having spent time on both sides of the Atlantic I've tried to get at least somewhat familiar with both of them. To convert between them in my head, at least around most air temperatures, I use a quick approximation. As 32F is 0C, and for each one Celsius you move almost two Fahrenheit, you can roughly go from Fahrenheit to Celsius by subtracting 32 and dividing by 2 (or a little less to be closer). So 50F is approximately 9C (actually 10C), or 86F is approximately 27C (actually 29.4C). It's not perfect, but it's often good enough if you're trying to work out if it'll be hot out. To go from Celsius to Fahrenheit, it's the reverse, times by 2 and add 32.

There are also at least two simple anchor points that can help just by swapping the digits around:

Both scales are now defined relative to the Kelvin scale, which sets the lowest point of 0K at absolute zero, where basically all movement stops. Zero on the Kelvin scale is around -273C. As such, the Kelvin scale, though helpful for scientists, is not very practical for discussing the weather.

Fahrenheit and Celsius

A school science refresher: the 3 primary states of matter, solids, liquids and gases and the transitions between each one. If you’re like me you probably forget about the more obscure sublimation and deposition directly between solids and gases. And vaporisation of a liquid is evaporation, occurring at the surface, if it is below boiling point, otherwise it’s boiling.

There are some more unusual states including plasma — seen in lightning and fluorescent lights — and Bose-Einstein condensates, but mostly we’re familiar with ice cubes, water and steam.

States of matter

Life on a nuclear submarine is life under some pretty intense constraints. For one, there’s not naturally any fresh water and any time you use it the waste water builds up in the tanks and then has to be expelled, and when you expel it that makes noise, and because nuclear subs don’t want to give away their location they do their best to minimise the number of times they have to do that. That means taking care of all fresh water.

The other reason to take care of fresh water usage is that they have to make it the whole time — any fresh water for cooking, cleaning or drinking has to be made from sea water. If you drink a glass of water on a nuclear submarine you’re probably drinking the most expensive glass of water you’ll ever drink because it’s been desalinated by a nuclear submarine.

Hence the submarine shower with a total of 20 seconds of water: 10s with the water on, turn it off while you soap and scrub and finish with 10s of rinsing. That’s it. For me it’s a nice reframe in how much you actually need when you take a shower, and it still works. So if you fancy saving water and energy you could give it a try.

Submariner Tom Lewis even wrote a song about showers on submarines.

Submarine shower

The tragedy of the commons is the all too common outcome of individuals making use of a shared resource and one of the true challenges of our times. The original scenario referred to commons land that soon becomes overgrazed as each individual tries to maximise their value from the share resource. The tragedy is that the overgrazed land is then ruined for all.

We see the effect, perhaps most perniciously, with invisible or hidden shared resources such as taking water from underground aquifers for irrigation, or overfishing of fish stocks in the sea. The same effect is at work with problems such as littering, or washing plastics into the sea, or polluting the atmosphere — while it’s easier for any individual to take another fish, leave their litter on the ground, let pollution run into a river or the sea, or not worry about air pollution, the tragedy is it can have the effect of ruining them for all of us.

When shared resources are moderated or governed fish stocks can be managed to recover, water supplies to replenish or pollution to be naturally treated.

For more, check out this 5 min video on the tragedy of the commons by TED-Ed.

The tragedy of the commons

The finger-dip test helps solve probably the biggest killer of houseplants: overwatering. So, I love this simple tip known as the finger-dip test, or the knuckle test, to determine if your plant needs watering. Sadly, it came too late for many of my plants, but perhaps not for yours.

Just dip your index finger into the soil near the stem of your plant up to about your first knuckle. If the soil feels dry and your finger comes out clean, then it’s probably time for some water. If the soil around your fingertip is still moist, then it’s time to sit back next to your plant with a good book and enjoy it.

I learned this from the good people at Patch Plants and their resident plant expert Alice Vincent (@noughticulture).

The finger-dip test to not overwater houseplants

Lake Effect Snow is a phenomenon where crazy amounts of snow can fall in massive storms on a lake’s downwind—leeward—side. Where the effect is pronounced, to the east of some of the Great Lakes in the U.S. (think Buffalo), it’s responsible for the regions known as the snow belt.

It works like this: Cold air blows over a lake. As the cold air passes over the warmer lake, it picks up water vapor from the water, which warms the air. This causes the air to rise and, in turn, cool, such that when it reaches the downwind side of the lake, it has become cold and moist. This simple change can lead to some incredible snowstorms dumping 2 to 3 inches of snow per hour. Satellite pictures show it in action pretty clearly.

If there is a rise in land elevation along the path of the cold air, the air can cool faster and increase the effect — and also cause a rain shadow. And if there’s a lot of convection and the air rises quickly, you can even get what’s called thundersnow—a thunderstorm in a snowstorm.

Find the weather interesting? Me too. Also see:

Yesterday’s weather (applying weather forecasting to productivity forecasting)

Know your cirrostratus from your altocumulus

For everyday weather-related phenomena explained, see Dennis Mersereau’s The Skies Above: Storm Clouds, Blood Moons, and Other Everyday Phenomena, Mountaineers Books (2022). Dennis is also the source of the lovely phrase Nature’s greatest snow machine.

Lake-effect snow

OK, this is not rocket science, but growing up, I tended to use kayak and canoe interchangeably out of ignorance. There are so many neat hybrid ways to get on the water now that nothing is as cut-and-dried as it once was. However, if you check the attributes in the sketch, you can be pretty confident you’ll get it right.

This sketch features in my book Big Ideas Little Pictures

Kayak vs Canoe: What's the difference?

Strahler stream order is a smart way of categorizing the size of rivers by tracking where tributaries join. 

Each time two tributaries of the same order join together, the river rises in order.

So, the start of a stream from a spring is the outermost branch—it's first order. When two first-order tributaries join together, the river is classified as second-order, and so on.

The largest river by Strahler stream order classification is the Amazon, which is an incredible 12th-order river. This means that at least two 11th-order rivers had to merge together before the river emptied into the sea. Huge.

Strahler stream order: Streams, rivers, the Amazon and how to organise them.

Moon pools are protected entrances to water that can even give the remarkable ability to enter from under the water.

First created to support drilling operations on offshore platforms, moon pools can include entrances on the decks or undersides of ships or an entry and exit for divers from permanent underwater research bases.

For underwater entrances, also known as wet porches, the trick is to pressurize the air around the pool to the same pressure as the surrounding water. The raised pressure keeps the water from gushing in and enables a swimming pool-like entrance even though you’re already below the surface.

I've never used one, but I'd absolutely love to. One of my earliest memories of a moon pool and corresponding bafflement and wonder was in James Cameron's 1989 film The Abyss. A moon pool features in the recent trailer for the remastered version of The Abyss

Moon pool

The International Load Line, formerly called the Plimsoll Line, is an internationally adopted system for ensuring ships aren’t overloaded. Safe loading levels vary depending on the salinity—how salty it is—and the temperature of the water.

The Plimsoll line

The rest just foes to the overflow. I learned this from our guide Eric on Mount Rainier. Very helpful if you’re hiking and looking to stay hydrated and conserve water. But actually I find it a sensible approach for every day.

Our bodies can absorb 1 cup of water in 15 mins

Whichever way you look at it, water is a remarkable substance.

Water sketches