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[00:00] why is it that on a sunny sea day on a [00:02] cruise ship literally thousands of [00:03] passengers will try to cram around a [00:05] tiny pool you'd have thought the cruise [00:07] lines would have Realize by now that [00:08] most people will want to congregate [00:10] around a swimming pool on holiday yet [00:12] they still insist on fitting one that's [00:14] minuscule especially when you consider [00:16] that thousands of people are probably [00:18] going to want to use it so what's going [00:20] on why are the swimming pools on cruise [00:22] ships so small cruise ships as we know [00:24] them are actually a relatively modern [00:26] invention they evolved when commercial [00:28] Aviation rendered the old ocean liners [00:30] obsolete practically overnight demand [00:32] for passenger Transportation by sea [00:34] plummeted so the liner companies were [00:36] forced to adapt their business model [00:38] attracting people that were wanting to [00:40] travel for pleasure rather than purely [00:42] as a way of getting from A to B those [00:44] liners may have had the odd indoor pool [00:46] for first class passengers to relax [00:48] while crossing the cold Waters of the [00:50] North Atlantic but when they evolved [00:52] into cruise ships suddenly it was a [00:54] different story with The Disappearance [00:56] of the class system everyone had equal [00:58] access to the open deck areas which [01:00] proved particularly attractive as ships [01:01] began cruising to hot exotic locations [01:04] operators soon realized that in order to [01:06] run a successful business they needed to [01:08] make the onboard experience more [01:10] pleasurable than their competition and [01:12] what better way than by adding luxurious [01:14] swimming pools on the open decks to let [01:16] overheating passengers keep cool the [01:18] pools needed to be on the open deck [01:20] because not only is that where there is [01:21] the most open space but also that is [01:23] where the passengers will want to use [01:25] them ready for a quick plunge after [01:27] basking in the Sun so that's great [01:29] surely you can just fit a couple of big [01:31] pools surrounded by loungers and [01:32] everyone would be happy well almost [01:34] everyone you see the water and swimming [01:36] pools has a couple of annoying [01:38] characteristics when it's on a ship it's [01:40] heavy it sloshes and it's incredibly [01:43] expensive one of the cheapest ways to [01:45] get fresh water is debunker from a Shor [01:47] side connection and at the time of [01:48] making this video you'd be looking [01:50] around 350 per ton somewhere like Miami [01:52] plus connection fees of course a [01:54] hypothetical Olympic siiz pul would [01:56] therefore cost at least $99,000 in water [01:59] costs a each time you wanted to refill [02:01] it and of course you would also need to [02:03] have the 22,000 tons of water stored [02:05] somewhere on the ship just in case you [02:07] get that dreaded announcement over the [02:08] tanoi attention ships company Code Brown [02:11] Code Brown liod deck midships usually [02:14] you can fix a Code Brown with chemicals [02:16] but occasionally it will involve [02:17] emptying and refilling the pool instead [02:20] anyway if we consider that an Olympic [02:22] pool contains around 2 and 1 half th000 [02:24] tons of water it leads us straight onto [02:26] the next issue water is incredibly heavy [02:29] the super of a modern ship is usually [02:31] designed to weigh less the higher up you [02:33] go simply because it doesn't need the [02:34] additional strength as you get higher up [02:36] as there's less ship to support up there [02:39] the addition of a large swimming pool [02:40] not only means that you need to support [02:42] that weight of water but you also have [02:44] the additional weight of the stronger [02:45] superstructure that's needed for the [02:47] pool the KnockOn consequence is that a [02:50] naturally heavier ship will have less [02:51] spare capacity for other things such as [02:53] fuel drinking water stores and [02:55] ultimately passengers at the end of the [02:57] day it's the passengers that earn your [02:59] ship ship Revenue so taking up all your [03:01] ship's weight capacity with facilities [03:03] may be counterproductive of course the [03:05] weight argument is compounded by the [03:07] fact that it would be high up on the [03:08] vessel hopefully it's fairly intuitive [03:10] that a weight high up will make a ship [03:12] less stable necessitating additional [03:14] weight low down to act as a bit of a [03:16] counterbalance that's easy enough as you [03:19] can add a load of ballast but ballast [03:21] doesn't earn you any money so there's no [03:22] point carrying loads as it would be at [03:24] the expense of Passenger carrying [03:26] capacity to make matters worse the [03:28] static weight of water is actually the [03:30] least of your worries a far more concern [03:32] is the dynamic weight through a [03:33] phenomenon known as the free surface [03:35] effect let's take a hypothetical pool at [03:37] the top of a ship and see what happens [03:39] when you lean over obviously a load of [03:41] it is going to flow out and ideally [03:42] straight over the side that's actually [03:44] one of the advantages of having pools on [03:46] the open deck but look at what's left in [03:48] the pool you've now actually got a wedge [03:50] of water with its Center gravity shifted [03:52] towards the low side of the vessel [03:53] effectively making the Leaning even [03:55] worse than it was before the wider the [03:57] pool the further out that wedge will be [03:59] and the worse the effect you can counter [04:02] it with additional balast down low in [04:03] the ship factoring in the potential [04:05] shift in the water but again it involves [04:07] you adding more ballast potentially at [04:09] the expense of fee paying passengers as [04:12] you can see a large pool can quickly [04:14] become a massive issue on a cruise ship [04:16] potentially needing significant [04:17] quantities of balance to counter instead [04:20] what the cruise lines do is they design [04:21] the pools to be a bit of a compromise [04:23] they'll be narrower in width to minimize [04:25] the free surface effect when the ship is [04:27] rolling lengthwise it isn't nearly as [04:29] bad because ships are naturally stable [04:30] that way anyway I mean have you ever [04:32] heard of a ship capsizing bow first so a [04:35] long narrow pool might work but it would [04:37] still weigh a ridiculous amount and [04:39] require a lot of strength up high in the [04:40] superstructure unlikely justifying the [04:43] structural compromises required instead [04:45] the best compromise seems to be a couple [04:47] of small plunge style pools where the [04:49] strength can be covered with minimal [04:51] amount of extra superstructure and the [04:53] deck design can split the ship up into [04:55] different areas making each pool appear [04:57] bigger than it really is in one sense it [05:00] looks like there are only a few tiny [05:02] pools on the upper deck but clever [05:03] design can make them feel bigger without [05:05] compromising too much on strength weight [05:08] and stability having shallower areas out [05:10] to the sides adds a lot of space for [05:12] paddling and children to play without [05:14] adding significantly to the depth [05:16] crucially though when the ship heals [05:18] over the free surface effect in these [05:20] pools isn't that different to a single [05:22] narrow pool in the middle of the ship [05:24] the greatest wedge of water is retained [05:26] near to the center line while a much [05:28] shallower wedge is formed further rout [05:30] if you need a deeper pool maybe for [05:32] acrobatics or something again we can [05:34] think carefully about where it could be [05:36] designed you want to restrict the [05:38] overall size to minimize the weight and [05:40] restrict the width in particular to [05:42] minimize the free surface effect you [05:44] also want to place it as low down in the [05:46] ship as you can to minimize the increase [05:47] in the ship's center of gravity due to [05:49] the pool so somewhere like the stern is [05:51] ideal compared to the upper deck pools [05:53] it can be so much lower down yet still [05:56] exposed to the Sun as you can see [05:58] there's an awful lot that goes into the [06:00] design of pools on a cruise ship so [06:01] although it looks like they've just [06:03] chucked a couple of little pools on as a [06:04] bit of an afterthought in reality [06:06] there's been a tremendous amount of [06:08] thought and consideration that's gone [06:09] into the design as always I'd just like [06:12] to end the video by thanking our plus [06:13] supporters on patreon your continued [06:15] support helps to keep these videos freeo [06:17] view across social media so thank you 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