[HN Gopher] The roller ship was not an effective way to cross th...
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The roller ship was not an effective way to cross the high seas
Author : Stratoscope
Score : 74 points
Date : 2024-03-30 06:42 UTC (1 days ago)
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| helsinkiandrew wrote:
| Reminded me of the 19th century Russian circular ironclads:
|
| https://en.wikipedia.org/wiki/Russian_monitor_Novgorod
| 082349872349872 wrote:
| If someone does a steampunk version of Star Wars, that'd be the
| Falcon design.
| mojomark wrote:
| "The general hope was that the roller ship would slash travel
| times by virtue of its low-drag design. Sadly, an attempt to
| cross the English Channel in 1897 revealed that the roller design
| had one unforeseen drawback. In the water, the rollers tended to
| drag a great deal of water up with them as they rotated."
|
| Super fun. I'm a marine engineer and design vessels. I've seen a
| lot of whacky designs over the years and never encountered this
| one!
|
| Apparently, from the above quote, the culprit for increased drag
| was skin friction (in this case, that meant water clinging to the
| surface of the rollers and being lifted out of the water - kind
| of like the reverse effect of a Tesla turbine which exploits skin
| friction between moving air and a stack of rigid discs on a
| rotor). That would certainly cause propulsive inefficiencies.
|
| However, from my view, the primary source of drag here are the
| "hollows" between the rotor discs. If you were to look at a plan
| (top) view of the vessel as it moves through the water you would
| find significant water pressure gradients between (at the aft and
| fore end of) each wheel. When you have multiple wheels in series,
| you have oscilating high and low pressure zones along the length
| of the waterline. That's a tremendous amount of energy lost to
| water turbulance.
|
| When you look plan views of hydrodynamic hullforms at the
| waterline (whether monohull, or multihulls like
| catamaran/trimarin/SWATH) or even aircraft foil shapes, you don't
| see "wavy" form lines for this very reason.
|
| I will say that these inventers were encroaching on the SWATH
| hull shape. The author states that this roller disc hull would
| not be stable due to the high CG. However, SWATH hulls are known
| for their stability in high sea states.
| LorenPechtel wrote:
| So many things are obvious once pointed out. I never would have
| thought of pressure gradients but once you did it's obviously a
| very uneven surface and you don't do that in anything
| contending with a lot of drag.
|
| How do you see this as a SWATH? This is a catamaran that
| combines buoyancy and propulsion. I do agree it has a high
| center of gravity, but that's a relative term--what counts is
| the ratio of height to width. And a catamaran or SWATH has a
| much wider base than a typical ship.
|
| Wikipedia says SWATH ships require complex control systems--
| why? Yes, they're very load sensitive because the small contact
| at the surface means a lot of vertical movement to compensate
| for weight changes, but couldn't that simply be handled with
| some pumps and tanks? Make the ship always weigh X--take on
| water or pump it out as needed to maintain that X.
| usrusr wrote:
| I'm not a marine anything, but I'd assume that the control
| system Wikipedia mentions are ballast tanks that need to
| reflect any change in load, load distribution and even wind
| load I'd guess. Sinking a little deeper won't do much to
| compensate increased load because the small surface area
| means little change in displacement per change in vertical
| position. Active trimming pumps.
| Someone wrote:
| I don't understand why they would think this to have low drag.
|
| - Displaced volume wouldn't be lower than that of a traditional
| ship (likely even quite a bit higher because the wheels would
| add mass and the hull would have to be stronger than one that
| rests on the water)
|
| - Surface area would be higher than that of a single hull.
|
| Also, looking at this as a variant on the paddle steamer (https
| ://en.wikipedia.org/wiki/Paddle_steamer#Seagoing_paddle...),
| didn't we already know in 1897 that screw propellers are a lot
| more efficient? SS Archimedes
| (https://en.wikipedia.org/wiki/SS_Archimedes) was built in
| 1839.
|
| So, what was the thinking? It being easier to have low rpm in
| steam driven engines, and that compensating for those
| disadvantages?
| eternauta3k wrote:
| Part of the drag scales with the relative velocity between
| the surface of the wheel and the water. If they move with ~0
| relative speed, drag is reduced.
| bluGill wrote:
| Paddels can he just as efficent as screws but only with
| mechanical comylexity which makes them unreliable.
| s1artibartfast wrote:
| Wheels add mass and cross sectional drag to my car, but
| rolling more than makes us for it.
|
| I assume the thought was similar.
|
| Some of the energy is lost to friction, some is lost to the
| motion of water.
|
| Imagine a ship where the hull sufface has the same relative
| velocity as the water. It would behave the same as a
| frictionless ship.
| usrusr wrote:
| Isn't it rather obvious that they thought friction was the
| main (or the sole!) component of drag? If displacement waves
| didn't exist, or did not cause meaningful drag, floaty wheels
| might even have taken over already in the age of sail.
| 082349872349872 wrote:
| For the high seas I had thought a design criterion was self-
| righting; is that only true for smaller vessels?
| s1artibartfast wrote:
| I don't even think it is true for small vessels. Catamarans
| and outriggers are absolutely not self righting.
| adonovan wrote:
| > the culprit for increased drag was skin friction
|
| You raise the question of whether Teflon-coated rotors might
| have improved the efficiency... but isn't the skin friction
| also the source of propulsion? Would eliminating the tendency
| to "drag a great deal of water up" also eliminate the tendency
| to make headway?
| cpeterso wrote:
| "In 2016 a Florida man attempted to run from Boca Raton, FL to
| Bermuda in a home-made, inflatable plastic bubble. Reza Baluchi
| had been warned by the Coast Guard that any efforts to attempt
| his journey would be futile and result in severe legal and
| financial retribution. However, Reza's convictions and ambition
| left him undeterred by such threats - he'd been waiting his whole
| life to do this and nothing was going to stop him. This is the
| story of that fateful journey as told by the man who attempted
| it."
|
| https://youtu.be/da6_LjiIzXk
| ricardobeat wrote:
| That video is so frustrating. The coast guard complains the
| "rescue" cost $144k, but nobody called for it, and then they
| sink $120k of private equipment for no good reason. What a
| waste of resources. No difference from people who cross the
| atlantic alone in a kayak but they don't get forcibly rescued.
| Animats wrote:
| "Damnation Alley" (1977) had the "Landmaster" [1], a large ATV
| with a roller ship mode. But that was an amphibious vehicle with
| some river crossing capability, not a ship.
|
| There are amphibious monster trucks. Here's a Russian one.[2] No
| props, just ridged tires. They're not great watercraft, but if
| you are crossing frozen ground and break through the ice over a
| lake, they can grind across the water and up onto hard ground.
|
| [1] https://youtu.be/26n3RsXNyKE?t=392
|
| [2] https://www.youtube.com/watch?v=3j7n00Xx38o&t=104s
| ChrisMarshallNY wrote:
| Argh. I just got PTSD from that reference.
|
| _Damnation Alley_ was _Plan 9 From Outer Space_ -level bad.
| bryanlarsen wrote:
| SHERP is a Ukrainian brand that used to have production
| facilities in Russia.
| pfdietz wrote:
| Drachinifel on these:
|
| https://www.youtube.com/watch?v=qNLf0yt0IHo&t=1559s
| jbm wrote:
| > Rather than turning quickly, the rollers labored and the craft
| could barely break a dozen miles an hour according to a
| contemporary account. Even for the late 19th century, that was
| slow
|
| This reminds me of a lot of my failed efforts to refactor code.
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