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Old 02-11-2010, 11:26   #16
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Well one video...I'm guessing that there wasn't really any question about making. As the others said, if there was there would be no coverage of it, as good as this video is for the cruise line, "Extra, extra, Royal Caribbean ship crashes into bridge causing mayhem" is not something you want a video of. Especially after the captains gives an interview like that.

Sill, some good seamanship there. I wouldn't want be in command for the trip.
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Old 02-11-2010, 12:14   #17
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Large bridges though change in height with respect to the Earth, depending on air temperature and traffic.
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Old 02-11-2010, 12:17   #18
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Sill, some good seamanship there. I wouldn't want be in command for the trip.
Isn't that like saying the person who leaves a secure harbor in a storm and survives is had good seamanship too?

What I'd like to know is whether or not there is another way around or if that was the only way the ship could go?
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Old 02-11-2010, 12:22   #19
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Indeed!
I don’t believe that “squat” can be precisely calulated; only very nearly estimated.
The "squat effect" is the hydrodynamic phenomenon by which a vessel moving quickly through shallow water creates an area of lowered pressure under its bottom that causes the ship to "squat" lower in the water than would otherwise be expected. This is due to a reduction in buoyancy caused by a downward hydrodynamic force created by flow-induced pressures. It is caused by similar forces as lift in aircraft, except that the low pressure area is beneath the hull. It can lead to unexpected groundings and handling difficulties.
Squat is believed to have been one of the causes of the 1992 grounding of the Queen Elizabeth 2 (QE2) off Cuttyhunk Island, near Martha's Vineyard. At the time of the QE2's grounding she was reportedly traveling at 24 knots (12 m/s) and her draft was 32 feet (9.8 m). The rock upon which she grounded was an uncharted shoal later determined to be 34.5 feet (10.5 m), which should have given her room to spare, if not for the "squat effect." NTSB investigators found that the QE2's officers significantly underestimated the amount the increase in speed would increase the ship's squat. The officers allowed for 2 feet of squat in their calculations, but the NTSB concluded that her squat at that speed and depth would have been between 4.5 and 8 feet.


I always wondered whether or not Gord knew "Squat" Now I'm sure of it.
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Old 02-11-2010, 12:36   #20
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Definitely more than 20 inches. I bet they very carefully measured to fit without the squat and took any squat that happened as additional clearance. They would have precisely measured the ship's lines and either gotten the real clearance from the bridge operator or sent out the ship's launch with a laser rangefinder. Nothing was left to chance (assumed based on the captain not being from some flag-of-convenience state).
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Old 02-11-2010, 12:36   #21
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If it really was that close, then I'm not impressed and don't think it took guts. It took stupidity. .
I think if you can build a ship costing millions you can work out the height of a bridge between you and the open sea

PR stunt to raise publicity for a new cruise ship, nothing more.

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Old 02-11-2010, 12:56   #22
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I always wondered whether or not Gord knew "Squat" Now I'm sure of it.
But that may not be exactly the same as "diddley squat".
Nonetheless ...
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Old 02-11-2010, 13:51   #23
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I cross-posted this to Facebook, spawning a discussion replete with references to formulae, and just concluded by writing this, which I just had to share here:

Next time I'm galumphing down a channel with the current behind me and no room to turn around, frantically shuffling through charts and cruising guides to get the bridge clearance, doing tide calculations and daylight savings time offsets in my head, and trying to remember my air draft including freeboard with current fuel load, I'll just glance at the depth-finder, consider whether conditions are shallow enough to support the squat effect, and gun it! My crew and passengers will dive off in all directions and paddle frantically to shore, and traffic on the bridge will halt in a pair of pile-ups, one on each approach, as everyone reaches for their cell phones in hopes of a viral YouTube hit.

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Old 02-11-2010, 14:16   #24
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This is an exciting combination of two incredible feats of engineering but it's not "gutsy" at all.

Absolutely nothing was left to chance.

A team of engineers worked this out before the ship was even built.

The "20 inches" figure makes for a good headline but it's misleading: 20 inches isn't the clearance, it's the known margin of error in the draft calculation.

The actual clearance was several meters.

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I think if you can build a ship costing millions you can work out the height of a bridge between you and the open sea
Actually it's a $1,500,000,000 ship and a $4,600,000,000 bridge.
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Old 02-11-2010, 14:22   #25
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A year ago, November 1st 2009, the sister ship "Oasis of the Sea" passed under the bridge. Quite a few similar borderline passages under the bridge has occurred, and the Danish authorities know the drill.
An official observing the passage last year said there was at least a "couple" of meters clearance. Even though the tide i minimal, probably less than a foot, last years passage was timed to take place at low water. Meteorological conditions has a greater influence on the water level than the tide in this area. The traffic on the bridge was temporarily stopped last year, as a safety precaution, presumably the same thing happened this time.
The clearance under the bridge is given as 65 m by the authorities and probably has some safety margin. Probably worst case scenario load and temperature wise + some margin.
So it was more of a carefully prepared and considered passage than the hyped impression in media.
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Old 02-11-2010, 18:43   #26
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I think if you can build a ship costing millions you can work out the height of a bridge between you and the open sea

PR stunt to raise publicity for a new cruise ship, nothing more.

Pete
My thought exactly.
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Old 02-11-2010, 18:45   #27
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I cross-posted this to Facebook, spawning a discussion replete with references to formulae, and just concluded by writing this, which I just had to share here:

Next time I'm galumphing down a channel with the current behind me and no room to turn around, frantically shuffling through charts and cruising guides to get the bridge clearance, doing tide calculations and daylight savings time offsets in my head, and trying to remember my air draft including freeboard with current fuel load, I'll just glance at the depth-finder, consider whether conditions are shallow enough to support the squat effect, and gun it! My crew and passengers will dive off in all directions and paddle frantically to shore, and traffic on the bridge will halt in a pair of pile-ups, one on each approach, as everyone reaches for their cell phones in hopes of a viral YouTube hit.

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Old 03-11-2010, 07:59   #28
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... The "20 inches" figure makes for a good headline but it's misleading: 20 inches isn't the clearance, it's the known margin of error in the draft calculation.
The actual clearance was several meters...
This sounds plausible, to me.
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Old 03-11-2010, 09:53   #29
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In doing stability and trim calculations, the margin of error in calculating draft is more like an inch or two. If you can read a draft mark at the bow and stern, you can nail it down to that.

A twenty inch margin of error could be enough to break a ship by having too much hog or sag. Even if you could not go out and read the draft marks, all ships have an onboard computer which does stability and trim calculations, which of course includes draft as either an input or a result of other parameters. With this software you can solve for anything given you have the other relevant variables entered.

http://en.wikipedia.org/wiki/Hogging_and_sagging
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Old 03-11-2010, 11:30   #30
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Its much trickier to estimate the height of the bridge than the ship.

"May 24, 1987. Over 800,000 people walk the Golden Gate Bridge celebrating it's 50th Anniversay. Overall, more than a million revelers found their way to The Bridge's 50th Anniversary fetivities, which began shortly after sunrise with a "Bridge Walk" and culminated at nightfall with a pyrotechnic fireworks spectacle. Over 800,000 people crammed onto The Bridge in a surprisingly fog free dawn. Their tremendous weight, the greatest load ever borne by The Bridge, caused the upward bow of the steel deck to flaten."
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