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Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 8:16 am
by JNJ
Hi,

Can a streamlined ship go underwater and then act like a submarine ? It would seem logical to me but I can't find any reference.
If not possible, why ?

Thanks.
JNJ

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 8:22 am
by arcador
A ship is completely sealed, so I see no reason not to.
Perhaps the pressure will cause some effects and the movement would be slower.

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 8:35 am
by Annatar Giftbringer
The Harrier commerce raider book has an entry on underwater operations. Short answer (due to being at work):

Yes, streamlined ships can function underwater, but they’ll start to leak a bit at approx 50 m depth. At 100 m, the leakage is more serious.

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 8:54 am
by JNJ
Thanks to both of you.

I just found the reference in the Harrier book. It answers well my question.

JNJ

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 11:03 am
by RogerMc
I'd say roughly as well as a WW2 and early Cold War non-nuclear submarines (which as anyone who has seen Das Boot will know is less well than you probably think).

One issue however is that your spaceship is sealed against vacuum and not against pressure and that any powerplant produces excess heat that is presumably vented quite safely in space but has nowhere to go underwater.

The War Stories podcast actually did a short programme about Soviet non-nuclear submarines during the Cuban Missile Crisis which as they were being actively hunted by US ships dropping dummy depth charges to let them know that they knew they were there had to seriously exceed the recommended period spent deep underwater and very quickly turned into ovens (link https://play.google.com/music/m/D27yk44 ... ar_Stories - you'll find it on itunes etc as well) - and this nearly broke the unit commander who was ready to surface and launch his nuclear torpedo (yes the Soviets had nuclear torpedoes) at his tormentors.

We were all saved from nuclear war by the 2nd in Command - who had also been the 2IC of the K-19 Widowmaker sub the previous year (i.e. the guy played by Liam Neeson in the film) and so arguably saved us from Armageddon twice - and contra to how Hollywood would handle it the Political Officer who both argued him down.

Try and use a scout/courier as a submarine at any serious depth or any serious time and you'd presumably get unfortunate stuff happening.

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 12:26 pm
by Condottiere
We can go skinny dipping in gas giants.

And at one time, we had submarines equipped with meson bays.

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 6:29 pm
by Yatima
Submarines are designed specifically to manage buoyancy by taking on water in tanks to dive and blowing water out of those tanks to surface. They also have control surfaces (hydroplanes and a rudder) that enable them to steer by changing the pitch and yaw of the boat on the surface and when dived.

So while starships may be waterproof to certain depths, you'd need to figure out how they dive if they are buoyant, and therefore float on the surface, how they surface if they are not buoyant and sink in an uncontrolled manner, and how they propel themselves through water and steer underwater if your expectation is that they do more than float on the surface or sit on the bottom.

J

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 7:39 pm
by Galadrion
Any ship, streamlined or not, can go underwater.

Now, how well it can function there and whether it can resurface may be another set of questions...

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 8:19 pm
by AnotherDilbert
It's much easier to get rid of heat via conduction in water than via radiation in space.

The M-drive can vector its thrust, so drive and steering shouldn't be a problem.

Buoyancy is a problem. If we can skim fuel, we can take on water into the tanks for a bit of control. Traders with empty holds should have very positive buoyancy, heavily armoured ships should sink like stones.

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 10:12 pm
by phavoc
Two things to think about are pressure and mass. As AnotherDilbert pointed out, a ship with collapsed matter armor would be too massive to float. A ship with armor factor one might be more easily able to float. The illustrations have certainly shown that over many versions. Now, one thing that would for sure allow it to work would be turning on your contragravity lifters. Then you could easily 'float' in water. Turning them off would mean sinking to the bottom. Which gives refs a way to have the ship stuck to the bottom of the ocean if the suction of the seafloor is greater than the lifting ability of the contragravity (pure speculation since we have no specs).

The other issue is pressure. Cargo ships especially have airlocks designed to handle vacuums and entering a planetary atmosphere with pressures of 1, maybe 2 atmospheres (gas giant skimming included). The pressure in salt water (it varies with fresh water) for 10m is 1 atmosphere. At 100M it's 10 atmospheres, at 500M it's 50 atmospheres. Submersibles are designed specifically to handle pressure - other vehicles such as spacecraft aren't - though the higher armor factor a ship has the more it's frame is designed to take hits on the surface and channel the energy through the frame to prevent buckling. This would be equivalent to help stave off crushing by depth. Keep in mind that the cylinder is optimized to resist pressure, but other forms, like large swathes of flat hulls, will increase the crushing pressure.

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 11:18 pm
by Pyromancer
From Futurama, when their spaceship is pulled under water:
"How much pressure can the ship take?"
"I don't know, but it's a space ship, so I'd guess between zero and one atmospheres."

Re: Can a streamlined ship go underwater ?

Posted: Thu Mar 29, 2018 11:29 pm
by AnotherDilbert
phavoc wrote: Now, one thing that would for sure allow it to work would be turning on your contragravity lifters. Then you could easily 'float' in water.
If you assume that is standard equipment (I don't).

Contra-gravity is the TNE system that did not provide thrust, only lift. MgT uses anti-gravity that provide both lift and thrust. It is not specified whether spacecraft have it, or if they rely on their M-drive.

phavoc wrote: The other issue is pressure.
I agree spacecraft are designed to keep pressure in, not out, and not a lot of pressure at that.

Borrowing from T5 Submersible is a selectable property of the hull that costs 2% of the ship's volume at MCr 1 / Dt. Crush depth is determined by the armour factor.

Re: Can a streamlined ship go underwater ?

Posted: Fri Mar 30, 2018 12:53 am
by Condottiere
Creation of gravity is basically artificial gravity; whether lifters can go positive instead of negative, or whether you'd have to install a separate set is left open.

Re: Can a streamlined ship go underwater ?

Posted: Fri Mar 30, 2018 1:51 am
by phavoc
AnotherDilbert wrote:
Thu Mar 29, 2018 11:29 pm
phavoc wrote: Now, one thing that would for sure allow it to work would be turning on your contragravity lifters. Then you could easily 'float' in water.
If you assume that is standard equipment (I don't).

Contra-gravity is the TNE system that did not provide thrust, only lift. MgT uses anti-gravity that provide both lift and thrust. It is not specified whether spacecraft have it, or if they rely on their M-drive.
I'm a bit puzzled by your statement. Are you saying that anti-grav capabilities are ONLY when a M-drive is activated? Contra-gravity is another term for anti-gravity. Though if you want to go back to the Space Vikings books, the lift portion of the drive was separate from the maneuver, power plant and jump drives. If an air/raft is capable of anti-grav floating, a starship should be as well.

Re: Can a streamlined ship go underwater ?

Posted: Fri Mar 30, 2018 10:03 am
by AnotherDilbert
phavoc wrote: If an air/raft is capable of anti-grav floating, a starship should be as well.
Not necessarily, M-drive and anti-gravity-drive are two separate systems, as the detailed design systems in MT, TNE, and T5 makes clear.

MgT (and CT) makes no mention of spacecraft having anti-grav drives.

You can of course assume whatever you want in YTU; I don't assume that spacecraft automatically have anti-grav drives unless they install a specific anti-grav drive.

phavoc wrote: I'm a bit puzzled by your statement. Are you saying that anti-grav capabilities are ONLY when a M-drive is activated?
Anti-gravity drive is not an intrinsic property of the M-drive, it's a separate system. Spacecraft need no anti-grav drive at all.

phavoc wrote: Contra-gravity is another term for anti-gravity.
Anti-gravity ≠ Contra-gravity.

Anti-gravity drive is used in CT, MT, and MgT and provides lift and thrust, so that a craft can move with anti-grav drive alone, like a helicopter.

Contra-grav is used in TNE, and neutralises most of the gravitational pull, but does not provide any thrust (like a balloon). A craft with contra-grav cannot move, but needs another drive for thrust, such as a rocket or jet engine (or M-drive).

Re: Can a streamlined ship go underwater ?

Posted: Fri Mar 30, 2018 11:15 am
by Condottiere
I think that Advanced and Primitive options unified the three variations of gravity based manoeuvre drives.

Not to say you couldn't install each separately and operate simultaneously.

Re: Can a streamlined ship go underwater ?

Posted: Fri Mar 30, 2018 2:45 pm
by rust2
According to the core rules, page 6:

"TL 13 (Average Stellar): The battle dress appears on the
battlefield in response to the new weapons. Cloning of
body parts becomes easy. Advances in hull design and
thruster plates means that spacecraft can easily go
underwater.
Jump 4 travel."

This is how I handle it in my setting. A ship of TL 13+ can operate underwater, a ship of TL 12- can only float on the surface or sink to the bottom.
In my mind this is good enough for gaming purposes.

Re: Can a streamlined ship go underwater ?

Posted: Fri Mar 30, 2018 4:03 pm
by phavoc
AnotherDilbert wrote:
Fri Mar 30, 2018 10:03 am
Not necessarily, M-drive and anti-gravity-drive are two separate systems, as the detailed design systems in MT, TNE, and T5 makes clear.

MgT (and CT) makes no mention of spacecraft having anti-grav drives.

You can of course assume whatever you want in YTU; I don't assume that spacecraft automatically have anti-grav drives unless they install a specific anti-grav drive.

Anti-gravity drive is not an intrinsic property of the M-drive, it's a separate system. Spacecraft need no anti-grav drive at all.

Anti-gravity ≠ Contra-gravity.

Anti-gravity drive is used in CT, MT, and MgT and provides lift and thrust, so that a craft can move with anti-grav drive alone, like a helicopter.

Contra-grav is used in TNE, and neutralises most of the gravitational pull, but does not provide any thrust (like a balloon). A craft with contra-grav cannot move, but needs another drive for thrust, such as a rocket or jet engine (or M-drive).
Here's the problem. Starships that have no inherent ability to counteract gravity would never be able to land and operate near cities - especially the futurisitic cities with 110+ floor buildings adjacent to (and surrounding) a starport. Starships are't tail sitters, and they cannot land as normal craft. Not to mention that some of the docking structures would require them to be able to float into/out of them. The capability must be implied. As we've seen in the various MGT publications they have left out wide swaths of details. Illustrations in rule books should be taken to show implied capabilities. That is a reasonable assumption to make.

It's true a spacecraft does not need anti-grav. However those that takeoff and land on planets will need it (insofar as we are talking about the ones in the CRB and other supplements).

Anti-gravity does in fact equal contra-gravity. How? By the definition of the words. Contra means 'against'. Anti means 'against'. The terms, at least as far as the dictionary is concerned, are equivalent. And in usage I would say they are also equivalent since they each are applied to systems that work against gravity forces.

I agree that if a vehicle is equipped with anti-gravity capabilities it is capable of movement as well. Though this is where the rules are also quite fuzzy, as the capabilities of the systems are never defined. Again players are left to make assumptions and inferences because the designers failed to provide sufficient details.

None of this is made any easier with the jumble of rule sets and the inconsistency across them. Though I suppose it does make for some interesting forum fodder. :)

Re: Can a streamlined ship go underwater ?

Posted: Fri Mar 30, 2018 7:52 pm
by AnotherDilbert
phavoc wrote: Here's the problem. Starships that have no inherent ability to counteract gravity would never be able to land and operate near cities - especially the futurisitic cities with 110+ floor buildings adjacent to (and surrounding) a starport.
They can: the Starship Operators Manual, Vol. 1 explains this in detail. I believe it is canon. Explicitly ships do not have anti-gravity drive in MT.

phavoc wrote: That is a reasonable assumption to make.
I have noticed that many want to make that assumption, and you can of course do as you wish in your game. It is not necessary for Traveller to work.

I believe MgT2 avoids these details to allow players to play as they wish which is why I noted that it is you can assume it or not:
AnotherDilbert wrote: You can of course assume whatever you want in YTU; I don't assume that spacecraft automatically have anti-grav drives unless they install a specific anti-grav drive.

phavoc wrote: Anti-gravity does in fact equal contra-gravity. How? By the definition of the words.
They are two different technical systems with different functional details, even if the names are similar.

phavoc wrote: None of this is made any easier with the jumble of rule sets and the inconsistency across them. Though I suppose it does make for some interesting forum fodder. :)
All of this is clearly defined in editions that care about detail, e.g. MT, TNE, and T5.

Re: Can a streamlined ship go underwater ?

Posted: Fri Mar 30, 2018 7:54 pm
by AnotherDilbert
rust2 wrote: According to the core rules, page 6:
Thank you, that seems to settle the issue.