2935: Ocean Loop

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Ocean Loop

Title text: I can't believe they wouldn't even let me hold a vote among the passengers about whether to try the loop.

Explanation

This explanation may be incomplete or incorrect: Created by a GULF STREAM JET - Please change this comment when editing this page. Do NOT delete this tag too soon. If you can address this issue, please edit the page! Thanks.

The comic shows a large construction, rising out of the sea to dwarf a nearby cruise ship. It involves a submerged water-jet sending water up out of the surface and round a rollercoaster-loop-like water-flume trough. The scale is such that it seems that the ship, once caught in the necessarily powerful stream of water, is intended to itself be propelled around the inverting loop before 'safely' exiting at the other side.

Apart from various other issues regarding Template:what-if, the stream of water required to maintain this setup would be acting upon the nearby water and so the nearby ship is probably already close enough to be drawn into the loop (with the best option left being to deliberately steer into it, rather than risk being swept uncontrollably into the structure), assuming that it isn't already caught in the tug of the water-jet's inward flow.

Even assuming a 'successful' loop (the stresses, and rotation, inflicted by the loop are likely beyond the design limits of such a vessel), the emergence back into the relatively calm and stationary waters beyond the exiting outflow would be a severe challenge to navigation. On the positive side, due to the nature of buoyancy, if the loop structure itself is capable of withstanding the force of the water being forced round it then it should be equally capable of withstanding the passage of the ship, unlike an impromptu rail-based loop which might stand up on its own but then shake itself apart when the first carriage is sent around it.

The title text suggests that the not only are those in charge of the ship skeptical about sailing into this loop, but that they are worried that opening the decision-making process to the passengers might favour the risk over (well-founded) reason.

The comic depicts a cruise liner approaching what appears to be a massive aquatic loop-de-loop. Under the water, a giant pump is pushing the water around the loop, presumably at very high speeds. The bottom text, "I don't know why the cruise line fired me", implies that Randall either suggested or implemented this idea, much to the dismay of his company.

In reality this would be extremly problematic and dangerous for a number of reasons. First, because of the size and speed of a cruise ship, the ship likely wouldn't make it around the loop without falling off. Second even if they managed to make it through without falling, many of the passangers would abtain extreme injuries and/or likely fall off the ship all together (unlike rollercoasters the passengers aren't strapped down). Third, because of the way the loop's designed, several hundreds (if not thousands) of tons of water is being launched onto the top of the cruise ship at a high speed. Needless to say, this would not only likely capsize the ship, but would also flatten any passenger on the deck.

Transcript

This transcript is incomplete. Please help editing it! Thanks.

[A cruise ship aproaches an enormous loop-de-loop flume. A large jet of water is being propeled into the loop-de-loop]

[Caption below the panel:]

I don't know why the cruise line fired me

Trivia

• This trivia section was created by a BOT
• The standard size image was uploaded with a resolution/size larger than the supposed 2x version.
• This may have been an error.
• At the time of posting, the image was huge, 4760 x 4295 pixels.

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Discussion

The 'standard' and '2x' sized images had unexpected sizes, so a Trivia section has been automatically generated, and an imagesize parameter has been added (at half size) to render the image consistently with other comics on this website. --TheusafBOT (talk) 20:47, 20 May 2024 (UTC)

We're still calling 4760 x 4295 "massive" in a time when many tvs and monitors are 4k? I mean I guess it's technically massive compared to the website's default, a downright embarrassing 635 x 573 -172.71.255.7 19:37, 21 May 2024 (UTC)

1475: Technically 20 million pixels are technically massless, not massive. 172.71.98.46 19:49, 21 May 2024 (UTC)

Reading this on a WXGA (1366x768) laptop screen here 172.69.130.225 13:36, 28 May 2024 (UTC)

Bad bot EDIT: Oops, wording threw me off, it did the RIGHT thing this time! Bravo! "Standard size" made me think it had generated/found a regular sized image and saved THAT again! NiceGuy1 (talk) 06:14, 25 May 2024 (UTC)

Is there anyway to get notifications when a new comic comes out? I'm always late to these 21:27, 20 May 2024 (UTC)Jush

I believe that there may be a Twitter (or X, or Xwitter, whatever we're calling it out) announcement direct from Randall's account, but I don't use that myself. And, like me, you were here right as it came out, more or less, so so don't worry too much. You could write your own BOT-like poller (various ways, but do at least considerately throttle it back to checking perbaps no more frequently than every 15 minutes, 'cos too many people doing that would be 'problematical'), if you can't find a push-notifying service that does most of the hard work for you (and a whole host of other subscribers). 172.70.85.241 22:23, 20 May 2024 (UTC)

You can use the RSS feed: https://xkcd.com/rss.xml Val (talk) 04:07, 21 May 2024 (UTC)

Happy Victoria day to anyone else in Canada! 162.158.146.235 21:39, 20 May 2024 (UTC)

Due to not being told about any Edit Conflict, I managed to co-edit the initial explanatuon with A.N.Other (sorry, haven't checked who, probably the first major editor in the page-history). I've put the most useful bit (IMO) of their article into mine, but some of it seemed wrong. Or at least not right.

• "because of the size and speed of a cruise ship, the ship likely wouldn't make it around the loop without falling off" - well, given the mass of water nicely holding itself to the loop, a ship floating around in it at the same speed would be holding itself to the loop quite nicely (moreso, perhaps, with its CoG taking a tighter loop than the fluid-loop).
  • Of course, it could be slower, but that would mean fighting the current. Whatever huge velocity the water is going, you'd have to be capable of going full-reverse at significant speed to overcome that,
    • Well, you could be just less than the just more than fast-enough water, but it's probably significantly faster than loop-speed, or a lot of edge-surface water would shed out of the topmost loop-trough due to fluidic friction against the trough itself.
    • And there's the acceleration needed to match the fluid flow-rate, but that causes problems before 'falling off' is an issue. Imagine suddenly finding yourself going hundreds (thousands?) of knots sternwards in still water. Probably what it'd feel like, before even getting to the tilt (by which time, any ship that had survived is probably now close to water-speed).
• "Second even if they managed to make it through without falling, many of the passangers would abtain extreme injuries and/or likely fall off the ship all together (unlike rollercoasters the passengers aren't strapped down)" - If you experience negative Gs in a rollercoaster, it's not a true loop (just an awkward inversion). You should normally always stay at positive Gs, albeit at somewhere within 0<Gs<1 (which feels like negative, but is just short of weightlessness). Being strapped in is still important, but mostly for forces lateral to "local down" for where you are on the ride.
  • ...or, of course, if the ride malfunctions and leaves you stationary and inverted. Which happens, but that's not at all intended in most situations. There'd be no way an 'otherwise normal' flume-loop would do that, though refering back to the need of your ship to experience initial acceleration before it even hits the loop (and final deceleration once it exits it).
• "Third, because of the way the loop's designed, several hundreds (if not thousands) of tons of water is being launched onto the top of the cruise ship at a high speed. Needless to say, this would not only likely capsize the ship, but would also flatten any passenger on the deck." - The sudden undersea current is going to be a problem, but it's not going to be directed over the ship (save completely over the ship, in the loop far above).
  • What you'll have is the turbulent local sea conditions. There'd be a 'standing wave-trough' in front of the point the jet of water is shown to emerge, itself probably a catastrophic problem for a ship, even an ocean-going one built in expectation of occasionally meeting rogue waves) and all the problems involved in traversing such rough seas. If your vessel can survive that (without spinning sideways and hitting the flume-trough, or breaking its back due to the extremely uneven and changing buoyancy along its length) then it's probably going to survive the much smaller amount of water that splashes 'over' its upper superstructure, compared to whatever relative mastrom of flow there will be passing under/against its (nominally) below-waterline hull.

I don't know how much 'reality' Randall has invested in this premise (I presume little, given the lack of pressure-trough in the 'still' water just short of the jet-emergence, nor any distortion in the sea surface wherever the jet originally sucked its water in from), but a lot of the issues of the looping-the-loop "What if" train will be the prime factors, plus maintaining general control (in river navigation, going downstream, between bridge piers, you really have to power your vessel forward, faster than the river itself, or risk losing yaw discipline on your craft). All the rest is icing on the cake of improbability. 172.70.85.241 22:23, 20 May 2024 (UTC)

It's a comic drawing after all, it's meant to illustrate the concept but leave the actual reality to our imagination. Conceptually it seems obvious to me that if the ship actually makes it through the loop, it exits fairly smoothly (class 2 or class 3 white water rafting).162.158.146.52

"...wherever the jet originally sucked its water in from..." - from the mains, obviously.172.69.194.204 11:05, 21 May 2024 (UTC)

The current paragraph on the title text seems off-base. It seems pretty clear to me that Randall had the idea, managed to get the loop constructed, persuaded the ship to sail to the vicinity (unless it was constructed on a previously planned route), and was attempting to persuade them to enter it before anyone realised it was a bad idea and objected. He then tried toorganise the passenger poll, and they shut that down too, and fired him. The suggestion that someone else randomly built the thing, separately from him trying to persuade them to use it, doesn't really make any sense.172.70.90.48 11:24, 21 May 2024 (UTC)

As a ballpark, spherical cow, estimate: To complete the loop, the centripetal force at the top of the loop has to equal the gravitational force of the ship. Centripetal force is mv^2/r, and gravitational force is mg, so we have v_top^2/r = g, v_top = sqrt(gr). At the top of the loop, the height is 2r, which means you have potential energy 2mgr, and kinetic energy 1/2 mv_top^2 = 1/2 mgr. Thus, at the bottom of the loop, you need kinetic energy 2mgr + 1/2 mgr = 5/2 mgr. This gives us the velocity at the bottom of the loop, 1/2 mv_bot^2 = 5/2 mgr, v_bot = sqrt(5gr). Call the cruise ship 300 m long, the diameter of the loop appears to be about 3 ship lengths, so r = 450 m. So the ship has to enter the loop at 150 m/s, 540 km/h, 335 mph. That's about Mach 0.45, which is probably the first time a cruise ship speed has ever been described with a Mach number. 172.70.135.75 13:03, 21 May 2024 (UTC)

Hopefully, they will also have handed out machs to all the passengers...172.69.43.131 15:12, 21 May 2024 (UTC)

The speed is probably much easier to achieve than it sounds, though, as the water will already by at a very high speed and the ship will only need to accelerate the difference between it's final speed and the water's. So we'd also need to find out the speed of the water to know what kind of engine the ship would need to achieve this. 172.70.162.17 10:41, 22 May 2024 (UTC)

We're probably not talking about ship-engine power at all (except to drift it into the jetstream effect). The best way might be to remodel the ship's stern into a giant 'pusher' plate (or deploy a huge, and tough, drag-chute from the bow) and rely upon the (from above) 0.45mach-speed water most effectively drag the ship up to (almost) its speed quickly enough to make the journey. This jet of water will already be dragging the water around it up to significant amounts of the speed (you'd probably want to msybe double the stream-speed to average it out at above looping speed for both jet and jet-adjacent water dragged into the system).

The ship will already by floating in an unnaturally heavy current at the point we picture it, probably unable to even reverse out of it, and the best use of engines would be to merge 'nicely' into the full stream, and doing the equivalent of decelerating from some techmagically-indiced demi-supersonic rearward motion through stationary waters. Ship sterns aren't really designed to cut through water as much as bows are (and, even for the latter, often not anything like as fast) but exactly how it behaves would be complicated by many engineering and fluid-dynamics issues that the average ship would never be expected to encounter (or not more than any unlucky once!), so when this loop-the-loop is designed and built (for the ship company?) it'll probably require a simultaneous refit of some kind of other for the intended vessel(s). Though if the first has been done (without anyone noticing/caring), maybe the second also was (with the owners at least complicitly indifferent to the extensive dry-dock work). ...or so says my fanon on this issue. 141.101.98.164 12:51, 22 May 2024 (UTC)

There are human scaled water slide loopings, but they start by having the human drop vertically and then "only" loop up with ~45° inclination: AquaLoop. This probably would not easily scale to cruise ship sizes. Also starting the looping horizontally and going upwards may be a challenge to implement. --172.71.160.32 14:29, 21 May 2024 (UTC)

Could this be a reference to Cannonball Loop, the infamous looping waterslide that used to be at New Jersey's notorious Action Park (aka Traction Park or Class Action Park). 172.70.175.74 15:11, 21 May 2024 (UTC)

Glad I wasn't the only person who thought this, thank you! Have added a bit about it, not sure if it's that well-worded or in the right place but felt like it needed to be there, not least to introduce people to the astonishing horror show that was (Class) Action Park...172.70.163.120 15:22, 22 May 2024 (UTC)

Isn't this a giant https://en.m.wikipedia.org/wiki/Cyclonic_separation - device, where the ship will be smashed onto the bottom of the "track"? 172.71.160.30 (talk) 05:05, 22 May 2024 (please sign your comments with ~~~~)

Not how I think you envisage it. The ship is (by definition) no more massive than the water it displaces, so centripetal forces won't send it 'outwards' to hit the track-bottom. If it was a floating ball, it would remain on the curving surface, and never sink through thee stream. Cyclonic selarators merely exagerate the differences in density, and the simplified buoyancy equations do not give the ship any reason to 'sink' if it starts off floating. (This may channge if significant induced bubbles/cavitation in the water-jet itself reduced the density of the water, like a gas discharge beneath a ship can cause it to sink on otherwise calm seas.)

But, depending upon various rotational momentum issues, the rapid change of water-engle might not be matched by the 'localised relevelling' of the ship that makes it effectively nose-dive into the water (like the depictions of the Titanic, but faster) and then have the bow strike the chute-structure (although the flow of water might still be enough to directly counteract the angle and force it back). Whether this is survivable is another issue. And, if it doesn't happen, you've got a water piling up on(/over?) the stern so long as the relative waterspeed and shipspeed have it effectively steaming backwards at high velocity (and with a geometrically 'dipped' stern). 141.101.98.164 12:51, 22 May 2024 (UTC)

Its all fine and dandy if you want to "pretend" to die. (See the above video links.) In fact, the experiences are advertised as "fun". Yet the moment someone wants to try out the real thing, almost everyone throws a hissy fit. :( These Are Not The Comments You Are Looking For (talk) 02:36, 26 May 2024 (UTC)

Apropos of what links, may I ask? I must have missed that particular context. (Also hoping this isn't from personal experience, as this isn't really a good place or method to seek help or considerate recognition. Best we could ever do is point out better places and trust they work.) 172.70.160.249 08:50, 26 May 2024 (UTC)

Explanation, Paragraph three, Line two, "This video, among other potentially dangerous water slides, shows 2 such loop-de-loop water slides (1 and 2)." And no, not from personal experience of any kind. These Are Not The Comments You Are Looking For (talk) 19:38, 26 May 2024 (UTC)

Something's lost in transmission, then. Neither of the linked-to video(segment)s, or what follows, have anything to do with "pretending to die". Hence, it seems it's mentioned totally apropos of nothing. Glad we aren't to be worried about you, though. Strange phrasing rather left me wondering if you were heading in a different direction entirely. 162.158.74.48 23:19, 26 May 2024 (UTC)