TFA describes the Norwegian tunnel as "the world's first ship tunnel of any significant size", but "significant" changes as engineering advances, and Harecastle was certainly significant at the time - contemporaries thought it an unearthly achievement. Scepticism was such that it was nicknamed an "air castle" (after "castles in the air"). It was the absolute limit of what was believed possible with tunnelling technology through such rock: the 7ft width defined the size of locks and bridges for the rest of the Grand Trunk, or Trent & Mersey, Canal. In turn, this defined the size of the English "narrowboat", the dominant inland craft for cargo carrying and, since the 1960s, pleasure boating. (In modern terms this would be called "boat" rather than "ship", but in contemporary documents it was less clear, and it seems likely that the size was chosen as a half-ship - half the width of the Mersey Flat sailing vessels, on the river with which the canal connected.)
The original Harecastle Tunnel is now closed due to subsidence, but the 1820s replacement is still operational, and the rest of the Trent & Mersey Canal is fully navigable and very enjoyable: I moored a boat on it for six years.
(For anyone interested in finding out about Britain's 2,500-mile network of historic canals, here's the charity that runs them: https://canalrivertrust.org.uk/ )
Sure. The point is that this isn't a particularly significant "first" (as the original headline claimed), it's an incremental advance in tunnelling technology. If James Brindley had been able to build Harecastle to Mersey Flat dimensions, he would have done. But tunnels have steadily got broader, deeper, longer and air-draft-ier since Harecastle and Malpas. There was no sudden moment when someone invented and built the ship tunnel.
(Incidentally, the "general definition" you cite is one used by the US Naval Institute, but not universally recognised. As the former editor of a monthly news-stand boating magazine it's certainly not one I've ever used. In the UK, for example, you can legally define your small boat as a ship by signing up to the Small Ships Register.)
The Soviets had a neat submarine base that was a curving tunnel through a hill open to sea at both ends - now a museum. Designed to take a 100kt direct hit:
Actually, the UK did consider an underground base for its Polaris subs (probably around Lochalsh) but that got ruled out pretty quickly due to the enormous costs. The base also got relocated because the US wanted its UK submarine base to be close to an airport and the UK base ended up being close to the US base at Holy Loch.
Which is why the UK has its missile subs based so close to a major city!
See: The Silent Deep by James Jinks and Peter Hennessy
The volume of solid rock removed must be approximately 3 million cubic metres (1700 × 37 × 26.5 x ~2) rather than the 3 billion cubic metres described in the article.
Gate off the water for the canal separate from the sea, so that it doesn't fluctuate. Usually this involves building a set of locks so that ships can traverse between the different levels - basically, a pair of floodgates with mechanisms to drain water into and out of the pound between them. Push ship in, lock the near gate, drain or fill the pound, unlock other end.
You sure? 100 ships a day means 14 minutes per ship, and a lock cycle takes 10-20 minutes, so that's awfully suggestive to me. OTOH, I'm not sure of the relative difficulty and expense of adding height to a tunnel vs creating and operating a lock - I'd assume at some length it makes more sense to use a lock, since tunnel cost scales with length and lock cost doesn't.
I don't know why the limit is 100 per day, I'm just going by the article & the pictures in it which very clearly show a tunnel open to the ocean with no lock system.
The photos also show a mountain going straight into the ocean, which means raising the ship with a lock wouldn't save you any money, since you'd need an unbroken sequence of locks going all the way to the top of the mountain.
> But a storm surge would be unpredictable, right?
No we know what sort of storm surges are 10, 100, 1000 year events etc. At that point it's just a question of what you design the tunnel to withstand.
> How do the physics of "crushing" a boat by
> raising water level in a confined space work?
This is an elementary application of Archimedes' principle. The weight of the ship is equivalent to the weight of the water it displaces[1].
If the ship is stuck against the ceiling of a confined space the pressure it's excreting on the ceiling is going to be the equivalent to the displacement of that "extra" water.
1. Leaving aside the full calculation which takes the difference in the weight of air & water into account for the purposes of this explanation.
This reminds me of the Magdeburg Water Bridge, which is exactly what it sounds like - a bridge where a canal (big enough for large ships) crosses over a river.
Built in 1679, 165m long: https://en.wikipedia.org/wiki/Malpas_Tunnel
Built in 1832, 3333m long: https://en.wikipedia.org/wiki/Canal_de_Bourgogne
Built in 1927, 7120m long: https://en.wikipedia.org/wiki/Rove_Tunnel
The first two are canal tunnels not at sea level, but the last one is connected to the Mediterranean at sea level.