Comment by jug6ernaut | Hacker News Reader

Comment by jug6ernaut | Hacker News Reader

I regularly visit Port Aransas Texas, often fishing the shipping channel that goes to Corpus Christi. The channel can not handle the biggest of tankers, the supertankers. But even so, i can not overstate the size of these ships. It never ceases to amazes me. When you are in the channel you have to take into account them coming through the channel, and i dont mean simply getting out of there way, the channel is plenty wide to hold two(as they go both ways) with much space on both sides. I mean the effect they have on the channel, specifically when they are coming in (full of cargo). When full they draft a full 10-15' more of water. Displacing this much water causes mini tsunami in the channel. If you are to close to the bank you could either find yourself beached or slammed against something.

Its really a spectacle when they come by, even after seeing it hundreds of times i still stop and watch.

One thing not mentioned in this article which is a HUGE factor with moving these large ships is wind drift. Any boat /ship will act as a sail, but the bigger you get the harder it is to control. As anyone who has piloted any vessel can tell you it only takes seconds to get out of control. When moving these huge ships through such tight quarters i can only imagine how difficult it is to control.

I once got to experience the other end of that: Being on a ship while it's going through a tiny canal. In my case, it was the Kiel Canal in Germany.

(When you're standing on the deck of a ship, you can't see the small gap -- between ship and land -- unless you stretch your neck over the rail and look down.)

So imagine this: You've spent many days on the open sea, with nothing but water in every direction. It's become so normal to you that you forget there's other life out there, beyond the steel hull.

Then one morning you wake up from a deep sleep and step outside, and... You're surrounded by land! You can't see the canal beneath you, but you can see the beautiful park you're in, with joggers, mothers with strollers, and couples holding hands.

It's very bizarre, and I'm not sure I'd get used to it either.

Even transiting the Panama Canal in a smallish (210 foot USCG medium endurance cutter) is kind of weird. One day you're underway making way in the Pacific, the next day you've got mules pulling you through locks.

Other major consideration, especially in a narrow channel, is squat -- see http://en.m.wikipedia.org/wiki/Squat_effect

That takes balls:

"The second largest cruise ship in the world, Oasis of the Seas, used this effect as a contributing factor to pass under the Great Belt bridge, Denmark, 1 November 2009, on her voyage from the shipyard in Turku, Finland to Florida, USA.[5] Without the presence of the squat effect, the ship wouldn't have been able to clear the bridge safely - the margin would have been very slight. However, travelling at 20 knots (37 km/h) in the shallow channel, Oasis experienced a 30 cm squat, allowing sufficient room to clear the bridge safely."

So, you are captaining this brand new billion dollar cruise ship, and the deck of the bridge is too low to pass under it. Now, order your crew to speed up as much as they can, and trust physics to do its thing.

Yikes, gotta be confident about that one. Apparently the Oasis of the Seas is also able to retract it's chimneys (I'm sure that's not the correct word) to get a bit of extra clearance.

Video of this ship, and it's sister ship Allure of the Seas, going under the Great Belt Bridge:

https://www.youtube.com/watch?v=9Opr17Zw11E

In the old days of steamers they were smoke stacks/chimneys. These days the are more just for aesthetics afaik. Those they do put some instrumentation on them im sure. Such as GPS/radar/antennas.

Yes, but the basic technique is (at least) decades old. To transit some of the tighter bends of the Panama canal, ships used the hydraulic effects between the ship and the bank to either pull closer to one side, or as a cushion to push the ship over so it could turn in a smaller radius.

I've never heard of squat being used to make it under a bridge, though. We were just taught that if you were heavily loaded and close to the channel bottom, increasing speed could be a bad idea.

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