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Author Topic: How do warship Grav Decks handle thrust?  (Read 1840 times)

Weirdo

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Re: How do warship Grav Decks handle thrust?
« Reply #30 on: 05 December 2022, 16:50:42 »
I wondered if there might be no spokes at all, if it might resemble something more like a train, wrapped around a cylinder. But I'm not sure that jives with physics.

Space stations might use wheels, but all WarShip decks use this train approach, because a wheel's spokes would compromise a ship's structural integrity. They're boarded by smaller "cars" that are usually stopped, but when you get aboard they gradually accelerate to match the grav deck's velocity, and vice versa.

Yes, even the Wagon Wheel works this way. The "trains" and boarding cars are completely within those outer rings.
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Vehrec

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Re: How do warship Grav Decks handle thrust?
« Reply #31 on: 05 December 2022, 19:07:36 »
  How would those work?  a quarter of the deck, when stopped, would be upside down relative to the thrust, and half would be at 90 degrees from Down.
 That doesn't matter, because nobody's ever in a grav deck when the ship is under thrust, no matter which way it is oriented.
There's still stuff in there, and it needs to be secured unless you want to have it breaking lose and banging around.  So, yes it does matter, it matters a hell of a lot unless you want to have a treadmill rip lose, bash its way across the gym, and then punch a hole in a pressurized bulkhead that exposes the entire gravity deck to vaccum.
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Weirdo

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Re: How do warship Grav Decks handle thrust?
« Reply #32 on: 05 December 2022, 19:23:44 »
If it isn't firmly bolted to the deck, then the sailor who failed to secure it deserves to have their pay docked for the cost of the repairs, or otherwise punished accordingly, because every single one of them knows better. Putting things back when you're done so they won't fly around is just common sense in space.

And if it is bolted down and it breaks loose, the shipyard in question deserves criminal charges for negligence.
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cray

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Re: How do warship Grav Decks handle thrust?
« Reply #33 on: 05 December 2022, 19:30:28 »
Personally I struggle to visualize how that transfer car concept is engineered to work. I'm not questioning it, I just wish I had a model, or some art or a video, something that could help me conceptualize it.

Imagine that the gravdeck is a long chain of subway cars bent into a circle. It runs in an endless, circular subway tunnel somewhere inside the WarShip.

Right beside that tunnel is another circular tunnel. Instead of being filled with a complete, rotating circular train, it just has individual, elevator-sized cars.

1. If you're in the non-spinning part of the ship, press the call button like an elevator.
2. A transfer car pulls up to your door, docks.
3. Door opens, you float in, door closes.
4. Hit the transfer button.
5. Transfer car begins moving, running on track beside the gravdeck.
6. When the transfer car matches the speed of the gravdeck, it pulls up beside a door on the gravdeck and docks.
7. Door opens, you walk out, door closes.
8. Transfer car is free for another call.

Reverse to go back to the non-spinning parts of the ship.

Quote
I wondered if there might be no spokes at all, if it might resemble something more like a train, wrapped around a cylinder. But I'm not sure that jives with physics.

That's how gravdecks and transfer cars work in ships. There's no need for spokes at all. Physics doesn't care so long as you're spinning in that circle.

Quote from: Vehrec
Warship grav-decks don't have to be circumfural, do they?

...

There's still stuff in there, and it needs to be secured unless you want to have it breaking lose and banging around.  So, yes it does matter, it matters a hell of a lot unless you want to have a treadmill rip lose, bash its way across the gym, and then punch a hole in a pressurized bulkhead that exposes the entire gravity deck to vaccum.

Most gravdecks should be a ring around the KF core of a JumpShip or WarShip. When under spin, the floor should be aimed at the ship's broadsides. When under thrust, those floors will become walls, rendering the gravdeck uninhabitable. As you pointed out, care will be required in design of things like toilet lids. The issues of loose objects, piping, plumbing, etc. require attention to secure them, but they were largely solved by 1962. The RP Flip even retains usable bathrooms (toilets and showers) after gravity shifts 90 degrees on it:
 https://en.wikipedia.org/wiki/RP_FLIP

However, there's at least one exception to the "ring around the KF core" approach: Matt Plog gave the Athena off-axis grav decks in a way I never intended when I wrote up the ship. Those are still unusable under thrust but they could, in theory, have spokes to a central hub rather than using parallel transfer cars.
https://www.sarna.net/wiki/Athena_(WarShip_class)
« Last Edit: 05 December 2022, 19:36:13 by cray »
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Maingunnery

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Re: How do warship Grav Decks handle thrust?
« Reply #34 on: 05 December 2022, 19:36:03 »
Space stations have it easy, no substantial acceleration in any direction, so their construction can be very simple.
But for WarShips I imagine that each grav deck compartment can also rotate around the axis on which it travels, a bit complex but then they can simple adjust the speed and angle for any situation.
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cray

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Re: How do warship Grav Decks handle thrust?
« Reply #35 on: 05 December 2022, 19:37:10 »
But for WarShips I imagine that each grav deck compartment can also rotate around the axis on which it travels, a bit complex but then they can simple adjust the speed and angle for any situation.

No, gravdecks are simply stopped when a ship fires up its engines to any significant level of acceleration.
Mike Miller, Materials Engineer

**"A man walks down the street in that hat, people know he's not afraid of anything." --Wash, Firefly.
**"Well, the first class name [for pocket WarShips]: 'Ship with delusions of grandeur that is going to evaporate 3.1 seconds after coming into NPPC range' tended to cause morale problems...." --Korzon77
**"Describe the Clans." "Imagine an entire civilization built out of 80’s Ric Flairs, Hulk Hogans, & Macho Man Randy Savages ruling over an entire labor force with Einstein Level Intelligence." --Jake Mikolaitis


Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.

Maingunnery

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Re: How do warship Grav Decks handle thrust?
« Reply #36 on: 05 December 2022, 19:48:58 »
No, gravdecks are simply stopped when a ship fires up its engines to any significant level of acceleration.
Here is to hoping that any crew never has to deal with immediate thrust, or that will be very messy.
While simply stopping could be seen as a solution, it would not be a very practical one.
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Vehrec

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Re: How do warship Grav Decks handle thrust?
« Reply #37 on: 05 December 2022, 19:55:05 »
I don't see why it's so trivial to 'strap down' every object in a gymnasium so that it won't move when subjected to 3g acceleration in any direction in a complete rotation, nor why you should be surprised if the hundred-kilo appliance which is bolted down for 100 years using the same fasteners eventually decides it wants to take a tour of the room, if only due to metal fatigue in the fasteners.  Oh, and that weight rack, which holds all the big heavy weights when nobody is lifting them, it not only needs to lock them in place when not in use under all those possible accelerations, but it also needs to do that in a way that isn't easy for a 18 year old sailor 3rd class to ****** up.

I don't see why it's impossible to have a grav deck where the 'cars' of the segments can swing around to align with the direction of travel so they are still 'down' in the proper direction.  Hell, it saves having to duplicate every single thing inside the grav deck outside it, since by Cray's description they are unusable when there's any acceleration at all.

Also, how long does it take to start or stop a grav deck?  1000 tons doing 31 meters per second is a lot of inertia, do you just have brakes and dump all that into the entire ship?  How long does it take to empty the entire deck if the whole crew is in there, and need to get to action stations NOW?
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cray

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Re: How do warship Grav Decks handle thrust?
« Reply #38 on: 05 December 2022, 20:28:53 »
Here is to hoping that any crew never has to deal with immediate thrust, or that will be very messy.

Having the floor splay open and G-forces spike above 1G as spin and translation accelerations are added together isn't a safety improvement.

The only reason to not slowly brake a gravdeck before using 0.1G+ acceleration is that there's some threat that requires emergency maneuvering. That's not an environment where you want the gravdeck to keep spinning, adding its G-forces to those of the engines, and its gyroscopic headache for emergency maneuvering.

Quote
While simply stopping could be seen as a solution, it would not be a very practical one.

The engineering of a gravdeck that only operates in freefall and brakes otherwise is more practical than trying to make a gravdeck that accommodate shifting thrust and spin speeds. One fundamental issue is that a gravdeck has a single angular velocity - if one part of the floor is rotating at 3rpm then everything attached to it is rotating at 3rpm. However, as you begin to open up the gravdeck, giving it a highway-like bank, you run into the issue that different parts of the floor are at different radii from the center. This means the tilted floor has different effective gravities at different distances from the center of rotation.

A gravdeck that accommodates a single thrust or gravity (e.g., the gravdecks on Luna) can use a complicated curve so that there's more tilt further from the center. A single curve won't accommodate the wide range of accelerations available to WarShips.

You can try to make a rubbery deck with a highly adjustable curve but, ultimately, no one's going to keep the gravdeck spinning when a WarShip is lighting its drives on some emergency basis. Just hit the brakes and bring the deck to a halt as fast as reasonably possible without turning occupants into wall pizza rather than trying to turn it into a flexing, 1G+ stomach pumper.

I don't see why it's impossible to have a grav deck where the 'cars' of the segments can swing around to align with the direction of travel so they are still 'down' in the proper direction.

It's not impossible, just a complication that leaves you with crew areas with weirdly curved floors.

Quote
Hell, it saves having to duplicate every single thing inside the grav deck outside it, since by Cray's description they are unusable when there's any acceleration at all.

You could take a cue from the Flip or aerodynes like the Avenger and just relocate furnishings from one surface to another. Then you wouldn't have to deal with curved floors, either. Navies always like to keep their crews busy with makework like that, right?

Quote
Also, how long does it take to start or stop a grav deck?

There isn't a canon value. One minute / one turn seems like plenty - you could have brakes all the way around an internal gravdeck and slowing from 31m/s to 0 in 60 seconds induces minimal G-forces.

Quote
1000 tons doing 31 meters per second is a lot of inertia

The gravdeck tonnage refers to the necessary rotation equipment - the motors, bearings, brakes, transfer cars, etc. that make a gravdeck possible. Quite a bit of additional mass could be part of the rotating section, like crew quarters, cargo bays, armor, structural integrity, and whatever else is part of the spin section. So it could be well above 1,000 tons.

Mike Miller, Materials Engineer

**"A man walks down the street in that hat, people know he's not afraid of anything." --Wash, Firefly.
**"Well, the first class name [for pocket WarShips]: 'Ship with delusions of grandeur that is going to evaporate 3.1 seconds after coming into NPPC range' tended to cause morale problems...." --Korzon77
**"Describe the Clans." "Imagine an entire civilization built out of 80’s Ric Flairs, Hulk Hogans, & Macho Man Randy Savages ruling over an entire labor force with Einstein Level Intelligence." --Jake Mikolaitis


Disclaimer: Anything stated in this post is unofficial and non-canon unless directly quoted from a published book. Random internet musings of a BattleTech writer are not canon.

five_corparty

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Re: How do warship Grav Decks handle thrust?
« Reply #39 on: 05 December 2022, 22:41:58 »
Imagine that the gravdeck is a long chain of subway cars bent into a circle. It runs in an endless, circular subway tunnel somewhere inside the WarShip.

Right beside that tunnel is another circular tunnel. Instead of being filled with a complete, rotating circular train, it just has individual, elevator-sized cars.

1. If you're in the non-spinning part of the ship, press the call button like an elevator.
2. A transfer car pulls up to your door, docks.
3. Door opens, you float in, door closes.
4. Hit the transfer button.
5. Transfer car begins moving, running on track beside the gravdeck.
6. When the transfer car matches the speed of the gravdeck, it pulls up beside a door on the gravdeck and docks.
7. Door opens, you walk out, door closes.
8. Transfer car is free for another call.

Reverse to go back to the non-spinning parts of the ship.

That's how gravdecks and transfer cars work in ships. There's no need for spokes at all. Physics doesn't care so long as you're spinning in that circle.


Thank you!  I was also a little confused: i thought i had it, but this breakdown was perfect.

I have to rewrite a few paragrapghs, but, if I had a nickel everytime I've said THAT...  ;) ;D

idea weenie

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Re: How do warship Grav Decks handle thrust?
« Reply #40 on: 06 December 2022, 03:07:32 »
One thing I would expect on a grav deck is lots of padding on the decel side of stuff in the room.  I.e. if you need the room to stop ASAP then people and things are going to get knocked down in a certain direction (their momentum keeps them going while the deck stops).  So put decent amounts of padding on walls on that side of the grav deck, so people can impact with a couple inches of hard foam instead of the structural element that the foam was put on top of.

The accel side doesn't need as much padding as that will only be brought up slowly.

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Re: How do warship Grav Decks handle thrust?
« Reply #41 on: 06 December 2022, 06:09:06 »
In The Expanse, TV show and novels both. Not strapping stuff down is like being a poor spacer. It's like "living in space 101" stuff. I think the novels did a better job explaining it than the show did but it was noticeably a thing. A mistake to be called out if it was made.

On every deck of the warship in BT, just as the Expanse, not just the grav deck, you leave something "on the float" (floating around in zero-G) as the warship is stationary, zero-G. The warship goes from stationary to accelerating, potentially much greater than 1-G even, you have messes and potentially damage to the ship's "stuff" and crew all over the ship as every loose and floating object, large and small, comes crashing down.

So as a matter of standard operating procedure, everything needs to be strapped down.


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Re: How do warship Grav Decks handle thrust?
« Reply #42 on: 06 December 2022, 08:05:07 »
Exactly that. Either stuff is bolted down in such a way as to handle acceleration up to the ship's engine rating, when not in use it is secured in storage that can handle that, or heads roll. Those are your three options in spacecraft in Battletech.
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Maingunnery

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Re: How do warship Grav Decks handle thrust?
« Reply #43 on: 06 December 2022, 13:53:15 »
Having the floor splay open and G-forces spike above 1G as spin and translation accelerations are added together isn't a safety improvement.
floor splay open? What are you imagining?
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Daryk

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Re: How do warship Grav Decks handle thrust?
« Reply #44 on: 06 December 2022, 19:24:58 »
In The Expanse, TV show and novels both. Not strapping stuff down is like being a poor spacer. It's like "living in space 101" stuff. I think the novels did a better job explaining it than the show did but it was noticeably a thing. A mistake to be called out if it was made.

On every deck of the warship in BT, just as the Expanse, not just the grav deck, you leave something "on the float" (floating around in zero-G) as the warship is stationary, zero-G. The warship goes from stationary to accelerating, potentially much greater than 1-G even, you have messes and potentially damage to the ship's "stuff" and crew all over the ship as every loose and floating object, large and small, comes crashing down.

So as a matter of standard operating procedure, everything needs to be strapped down.
An excellent point!  I'm reminded of a West Wing episode where a Navy officer explained to a civilian the "why" of $300 toilet seats by literally breaking an ashtray.  His point was you pay for things breaking in a less dangerous way (the ashtray in question broke into (I think) three pieces, with no shards).  Operating procedures are CHEAP compared to materiel solutions...  ^-^

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Re: How do warship Grav Decks handle thrust?
« Reply #45 on: 06 December 2022, 22:00:14 »
Navies are probably very serious about paying top dollar for bolts that will hold a table to the deck even when subjected to 3-4 lateral or even negative Gs.

They might also go for frangible furniture that'll break quite easily instead of staying intact enough when it comes loose to punch through a bulkhead. Space isn't the place for oak.
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Cannonshop

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Re: How do warship Grav Decks handle thrust?
« Reply #46 on: 06 December 2022, 23:47:48 »
Navies are probably very serious about paying top dollar for bolts that will hold a table to the deck even when subjected to 3-4 lateral or even negative Gs.

They might also go for frangible furniture that'll break quite easily instead of staying intact enough when it comes loose to punch through a bulkhead. Space isn't the place for oak.

Au contraire, per scenes from "Isle of the Blessed" spaceships, especially combat spaceships, are outfitted with Oak AND Mahogany interior furnishings, and bone china tea-sets....at least, if you're the Word of Blake.
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Re: How do warship Grav Decks handle thrust?
« Reply #47 on: 07 December 2022, 05:43:53 »
And in the Twilight of the Clans novel that depicted the second space battle over Huntress. Warships can go full reverse.

The Invisible Truth did, to get broadside advantage on a Liberator, and the Starlight (Essex class)'s captain tried to go "full reverse" just before ramming a Vincent.

I don't mean flip and burn (use thrusters to rotate the hull 180 degrees and start burning in the other direction, eventually cancelling that forward momentum, then beginning to move in the new direction). I mean full reverse like a ship on an ocean, or a car in a parking lot.

The same novel also recycles several dialogue lines from the movie Gettysburg.

The novels are iffy on this stuff, is the point. To be fair back when I first read it decades ago, I barely understood a lot of this space stuff either, my frames of reference were Star Wars or Star Trek, and I don't recall seeing anything wrong with it back then. Now I know better.
« Last Edit: 07 December 2022, 05:53:27 by Alan Grant »

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Re: How do warship Grav Decks handle thrust?
« Reply #48 on: 07 December 2022, 07:18:55 »
Au contraire, per scenes from "Isle of the Blessed" spaceships, especially combat spaceships, are outfitted with Oak AND Mahogany interior furnishings, and bone china tea-sets....at least, if you're the Word of Blake.

Well the tea set certainly counts as frangible, I'd say. I don't know the math to check, but I'm reasonably certain it'll take a lot more than 2.5 Gs to put any of those pieces *through* a bulkhead before they shatter into dust, and I don't recall the WoB having anything faster than 3/5 in that system, at least mentioned onscreen.

As for the wood...here's hoping they've got really good restraining straps for storing that stuff.
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grimlock1

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Re: How do warship Grav Decks handle thrust?
« Reply #49 on: 07 December 2022, 08:37:08 »
And in the Twilight of the Clans novel that depicted the second space battle over Huntress. Warships can go full reverse.

The Invisible Truth did, to get broadside advantage on a Liberator, and the Starlight (Essex class)'s captain tried to go "full reverse" just before ramming a Vincent.

I don't mean flip and burn (use thrusters to rotate the hull 180 degrees and start burning in the other direction, eventually cancelling that forward momentum, then beginning to move in the new direction). I mean full reverse like a ship on an ocean, or a car in a parking lot.

The same novel also recycles several dialogue lines from the movie Gettysburg.

The novels are iffy on this stuff, is the point. To be fair back when I first read it decades ago, I barely understood a lot of this space stuff either, my frames of reference were Star Wars or Star Trek, and I don't recall seeing anything wrong with it back then. Now I know better.

Do the rules reflect this as well?

Au contraire, per scenes from "Isle of the Blessed" spaceships, especially combat spaceships, are outfitted with Oak AND Mahogany interior furnishings, and bone china tea-sets....at least, if you're the Word of Blake.

Funny story... When the USN was building the Iowas for World War II, they removed all wood furniture, after Pearl Harbor showed them that it was a fire hazard.  But they left the carpets in the flag spaces and oh, they stashed piles of shoring timbers everywhere
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Re: How do warship Grav Decks handle thrust?
« Reply #50 on: 07 December 2022, 10:02:56 »
Do the rules reflect this as well?

The answer is complex.

Under standard movement rules, spacecraft (WarShips included) can indeed use their max thrust when decelerating. Oddly enough, they aren't allowed to move backwards even in space - your forward velocity can be a positive number or it can be zero, but it can never be negative. Compromises for simplicity, one assumes.

Under the advanced vector movement rules, the bulk of your available thrust can only be used to thrust forward or to rotate, like a game of Asteroid. However, your can use your various maneuvering thrusters to expend one of your available thrust points in any direction, giving ships a limited ability to sideslip or decelerate without having to swing their butt trumpets around first. It's nowhere near max thrust, but getting a half-gee just from maneuvering jets is still pretty damned impressive when you think about it.
« Last Edit: 07 December 2022, 10:05:56 by Weirdo »
"Thanks to Megamek, I can finally play BattleTech the way it was meant to be played--pantsless!"   -Neko Bijin
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Daryk

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Re: How do warship Grav Decks handle thrust?
« Reply #51 on: 07 December 2022, 19:59:53 »
That's INCREDIBLY impressive for maneuvering jets!  :o

And last I checked (aboard ship), shoring timbers are still a thing...  ^-^

Cannonshop

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Re: How do warship Grav Decks handle thrust?
« Reply #52 on: 07 December 2022, 22:06:11 »
That's INCREDIBLY impressive for maneuvering jets!  :o

And last I checked (aboard ship), shoring timbers are still a thing...  ^-^

Let's see: Lighter than metal? check.
fewer scary gases if they catch fire than plastic? also check.

sometimes wood just works...but I'd suspect if they had something better that cost about as much? they'd use that instead.

On a wet-naval ship, your danger is the environment coming in at high pressure.  ON a space-ship, your danger is the environment getting out.

(unless you're smart and depressurize before combat, if that's the case, you want lots of cheap patch-plates so you can repressurize after you've finished killing the other guy...)

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Daryk

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Re: How do warship Grav Decks handle thrust?
« Reply #53 on: 07 December 2022, 22:12:27 »
If wood could be made air tight, it would be the choice...  ^-^

grimlock1

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Re: How do warship Grav Decks handle thrust?
« Reply #54 on: 09 December 2022, 13:19:49 »
And last I checked (aboard ship), shoring timbers are still a thing...  ^-^

I know. It just struck me as a wonderful example of "the Right way, the Wrong way, and Navy way."

Although I suppose if you have to start pounding plugs into holes and bracing hatches, I suspect everything in the compartment is probably thoroughly soaked.     
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Daryk

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Re: How do warship Grav Decks handle thrust?
« Reply #55 on: 09 December 2022, 18:11:12 »
Almost certainly.

Hellraiser

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Re: How do warship Grav Decks handle thrust?
« Reply #56 on: 03 January 2023, 19:28:31 »
And in the Twilight of the Clans novel that depicted the second space battle over Huntress. Warships can go full reverse.

The Invisible Truth did, to get broadside advantage on a Liberator, and the Starlight (Essex class)'s captain tried to go "full reverse" just before ramming a Vincent.

I don't mean flip and burn (use thrusters to rotate the hull 180 degrees and start burning in the other direction, eventually cancelling that forward momentum, then beginning to move in the new direction). I mean full reverse like a ship on an ocean, or a car in a parking lot.

...

To be fair back when I first read it decades ago, I barely understood a lot of this space stuff either, my frames of reference were Star Wars or Star Trek, and I don't recall seeing anything wrong with it back then.

1.  I need to re-read that battle, I don't recall that, but now I have this image of Beresick/Maverick screaming "We're going to put on the air-brakes & watch them fly right by".
  I would think they were using Maneuvering Thrusters & can't actually go "full" reverse but be limited to like 1MP or something similar to what Weirdo mentioned.

2.  I still remember reading the intro ASF fight in Sword & Dagger & having to re-read it like 5x to fully understand what the author was explaining.
  It was all about Zero-G closing distances & flipping multiple times to shoot coming & going & was hard to grasp at first.
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Daryk

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Re: How do warship Grav Decks handle thrust?
« Reply #57 on: 03 January 2023, 20:05:12 »
You can always flip if you need to apply full thrust...  ^-^