Talk:2935: Ocean Loop

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)

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)