World's largest cruiseship is shorter when underway

[Ekinodum]

The world's largest cruiseship has just been launched in Finland-

http://news.yahoo.com/s/ap/eu_world_s_largest_cruise_ship;_ylt=Ao4AlBcQtm53WM 6bRCc2aZGGWo14;_ylu=X3oDMTMxdWY3YnRpBGFzc2V0A2FwLz IwMDkxMDMwL2V1X3dvcmxkX3NfbGFyZ2VzdF9jcnVpc2Vfc2hp cARjcG9zAzcEcG9zAzcEc2VjA3luX3RvcF9zdG9yaWVzBHNsaw N3b3JsZHNsYXJnZXM-

It is only 1/2 meter shorter than the bridge it has to cross under to get to the ocean, so to ensure they get under safely they are going speed up when they approach the bridge! Yikes, I hope their engineers know what they are doing...

[Safe-Keeper]

It's not that she sits lower in the water, it's that she's got a higher chance of breaking through the bridge at flank speed:p.

Standard procedure, actually. They wait 'til low tide, then they speed up so that the ship lies lower in the water. How speeding up makes the ship run lower, I don't remember;).

[BenBurch]

It's not that she sits lower in the water, it's that she's got a higher chance of breaking through the bridge at flank speed:p.

Standard procedure, actually. They wait 'til low tide, then they speed up so that the ship lies lower in the water. How speeding up makes the ship run lower, I don't remember;).

Moving water = lower pressure.

Sucks the boat down.

[casebro]

How about the bow pushes the water aside, leading to lower pressure under the hull?

How do the engineers kniow how much, in a brand new boat that has never left it's home ancjorage before? Will it be enough?

[NoZed Avenger]

How about the bow pushes the water aside, leading to lower pressure under the hull?

How do the engineers kniow how much, in a brand new boat that has never left it's home ancjorage before? Will it be enough?

Math. I don't have the skills myself, but I am betting no one would risk something that expensive (boat OR bridge) if they weren't pretty darn sure.

[boooeee]

Silly engineers. Lorentz contraction is parallel to the direction of motion, not perpendicular.

[chaggle]

Canal effect. The props pull water from under the hull making the vessel sit lower in the water. It makes yachts go aground in canals. It's happened to me.

[The Central Scrutinizer]

Can't they just lower the water level?

[Toke]

Can't they just lower the water level?

Yes and no, somebody left it on automatic.:)

Both the speed and the propeller contribute to the increased draft.

One famous example* involved a bulk carrier being loaded on a river, the weight of grain was determined by reading the draft (that big ruler painted in each end of the ship)
At the destination a day later there were several thousand tons missing, and the crew were accused of embezzling.

It was obvious impossible and lead to more studies of squad effect (http://en.wikipedia.org/wiki/Squat_effect).

*freely from memory.

ETA: The ship was alongside but the river water was moving.

[ben m]

Can't they add stereotyped cruise ship passengers and an all-you-can-eat buffet ballast?

[dasmiller]

How about the bow pushes the water aside, leading to lower pressure under the hull?

How do the engineers kniow how much, in a brand new boat that has never left it's home ancjorage before? Will it be enough?

In addition to the 'math' (I prefer "engineering analyses"), there are facilities that build and test model ship hulls for just this sort of thing. I don't know for a fact that such tests were done in this case, but I'd be surprised if they weren't.

Of course, it's not that unusual for me to be surprised.

[Toke]

Can't they add passengers and an all-you-can-eat buffet ballast?

I guess cruise ships have rather small ballast tanks, their cargo tend to be light (compared to other types of vessel) and evenly distributed.
A container ship need enough tanks to compensate for quite a lot of bending, shear and torsion, depending on how inept the planners are.

My current RO/RO vessel require 24-32 tonnes of cargo/ballast for each cm of increased draft.
Bigger and other types of ships take more.

And no in spite of what you have seen in Speed 2 we do not have clothes lines, cctv, or light fixture in the ballast tanks.:D

[Toke]

BTW: I object to the term shorter, use lower.

Shorter is what happens if you sail full speed through a storm.
(Rare but it have happened)

[blutoski]

BTW: I object to the term shorter, use lower.

Shorter is what happens if you sail full speed through a storm.
(Rare but it have happened)

Or if you collide with something. That'll take a few feet of the length pretty fast.

Or... relativistic effects... doesn't the acceleration of the boat make it genuinely shorter from front-to-back?

[Toke]

I have just checked with the bridge, we may meet it sometime tomorrow afternoon in the baltic sea. We are going through Øresund for Estonia, they are heading for the great belt.

Or... relativistic effects... doesn't the acceleration of the boat make it genuinely shorter from front-to-back?
Yes, of course, but deck officers are not that good at physics and write it off to compression between the propeller trust and the resistance at the bow.

[ElMondoHummus]

Silly engineers. Lorentz contraction is parallel to the direction of motion, not perpendicular.

:dl:
Touché!!

In all seriousness, couldn't the explanation for sitting lower in the water at higher speed be done by manipulating the anti roll stabilizers so they deflect the ship down? Those stabiliers are basically underwater wings, after all (http://www.eurodamnews.com/2008/04/24/views-from-the-underbelly/) (scroll down at link for image).

[Beerina]

I presume their insurance company would put the nix on it if there was any chance of a problem. After all, loading it down with extra lead or cement wouldn't be all that much of a problem.

Assuming it wouldn't be dragging on the bottom of the river of course :)

[ElMondoHummus]

... so to ensure they get under safely they are going speed up when they approach the bridge!...


Silly folks, "they". Didn't they learn anything from weekends in dad's Chris-Craft?
http://forums.randi.org/picture.php?albumid=275&pictureid=1736

;)

I kid, I kid. I don't think they've ever designed any of these super huge cruise ships with planing hulls :D. Seriously, though, I think I might have overthought my earlier proposal. According to this link (http://www.datummarine.com/pdfs/86_hull_displacement.pdf), displacement hulls ride lower in the water as speed increases . So no dorking around with the roll stabilizers would be necessary, like I first thought.

[quixotecoyote]

:dl:
Touché!!

In all seriousness, couldn't the explanation for sitting lower in the water at higher speed be done by manipulating the anti roll stabilizers so they deflect the ship down? Those stabiliers are basically underwater wings, after all (http://www.eurodamnews.com/2008/04/24/views-from-the-underbelly/) (scroll down at link for image).

Is that before or after they reverse the polarity?

[Paul C. Anagnostopoulos]

Silly engineers. Lorentz contraction is parallel to the direction of motion, not perpendicular.
Which is exactly what I thought the OP was going to be about, what with the title "World's largest cruiseship is shorter when underway." I thought someone was going to measure the Lorentz contraction.

~~ Paul

[ElMondoHummus]

Which is exactly what I thought the OP was going to be about, what with the title "World's largest cruiseship is shorter when underway." I thought someone was going to measure the Lorentz contraction.

~~ Paul

How? If the observer is on the ship, he's in the same inertial frame and sees no contraction. If he's off the ship, he's awash in saltwater wake and his measurements will suffer accordingly. And if he's on land...

... oh, wait. That'd work. Heh... :o. Okay! Rant over; I found my answer. :D

Is that before or after they reverse the polarity?

You know, from what I understand, the electricity generators change polarity up to 240 times per second!!! :tinfoil

Er, wait... that's current flow, isn't it? Gah... everything I needed to know about real world physics I learned from Star Trek, which has has induced the problem of:
1: Creating a gap between perception and reality,
Second: Not actually having taught me accurate real world physics, and
C: Leaving me very confused as to why we don't have transporters and warp drive yet :boggled:.

[Bikewer]

How about this...."You there! You 10,000 people standing around doing nothing...Get on board!"

[Ekinodum]

Which is exactly what I thought the OP was going to be about, what with the title "World's largest cruiseship is shorter when underway." I thought someone was going to measure the Lorentz contraction.

~~ Paul


I was going to mention that, but I would then have had to post in the humor section. I'm pretty sure there are rules.

[JWideman]

All ships are "shorter" (lower in the water) when underway.

[Matthew Best]

Obviously they have to go faster, because global warming is resulting in higher sea levels - they need to get under that bridge as quickly as possible!

[666]

It's on its way...

VdmD9TQWFBc

[Toke]

We passed it around 1530, during my afternoon nap, and the bridge didn't call. :mad:

If you turn off the automatics for the stabilisers and operate the hydraulic valves manually it should be no problem to get them angled down in both sides.
The problem is that they are big enough to counter roll, but probably not to depress the ship significantly.

How about this...."You there! You 10,000 people standing around doing nothing...Get on board!"
Self propelled ballast ?:D
At 75kg each that would be 750tons, a ship that size (100.000tons displacement, 225,282 GRT) does not depres much from that.
If compared to my ships load table (26ton/cm at 10.000ton displacement) it would give all of 3cm.

[ElMondoHummus]

We passed it around 1530, during my afternoon nap, and the bridge didn't call. :mad:

If you turn off the automatics for the stabilisers and operate the hydraulic valves manually it should be no problem to get them angled down in both sides.
The problem is that they are big enough to counter roll, but probably not to depress the ship significantly.


Ah. Didn't know that. Good to know.


Self propelled ballast ?:D
At 75kg each that would be 750tons, a ship that size (100.000tons displacement, 225,282 GRT) does not depres much from that.
If compared to my ships load table (26ton/cm at 10.000ton displacement) it would give all of 3cm.


Too bad it didn't launch from some US port. If it were 10,000 of us Americans, you'd have a heckuva lot more mass. :D

... OW! Who hit me? Hey, I got a belly too! You all think I'm excusin' myself?? :lolsign:

[Toke]

The Finns got a nasty surprise when they realised the Great belt bridge were under way, their oil rigs were suddenly limited to 65m height, and they were too late to complain about it.
I am sure it it something they consider now before starting any shipyard project.

BTW: what is the point in cruise ships? Better food and regular shore leave?

[Dogdoctor]

Silly folks, "they". Didn't they learn anything from weekends in dad's Chris-Craft?
http://forums.randi.org/picture.php?albumid=275&pictureid=1736

;)

I kid, I kid. I don't think they've ever designed any of these super huge cruise ships with planing hulls :D. Seriously, though, I think I might have overthought my earlier proposal. According to this link (http://www.datummarine.com/pdfs/86_hull_displacement.pdf), displacement hulls ride lower in the water as speed increases . So no dorking around with the roll stabilizers would be necessary, like I first thought.

That is very interesting. I'm sure I have heard it before but so long ago I forgot. Displacement hulls move through the water in a depression created by the boat (oops ship I mean:) ) I guess they push the water out of the way creating a cavity in the water that they sit and move in. Cool.

[The Central Scrutinizer]

How about this...."You there! You 10,000 people standing around doing nothing...Get on board!"

Or the 10,000 people on board need to jump up and down at the same time.

[ponderingturtle]

All ships are "shorter" (lower in the water) when underway.

unless it is a hydrofoil.