How deep can you go?

[GJD]

I would imagine that making a ship vaccum sealed and waterproof are two different things, and that the corrosive effect of salt water would play havoc with sensitive ship systems.

Not at all. Those ships are designed to scoop GG's at hyper-sonic speeds. There is no sensitive ship systems exposed. If a ship can only survive 0-1 atmos, you are dead the next time you skim in a GG..

Who says scooping is done at an altitude where the pressure is anywhere near 1 atm? Streamlining will still be required at 0.1 atm, but hypersonic speeds will mean you are still collecting loads of atmosphere in your scoops. I'm sure the flow rate vs. scoop size vs speed calculations are relativly straightforward, and I would imagine there is an atmospheric composition chart showing altitude, pressure and ppm hydrogen somewhere. Those inclined could probably work out exactly how long and how fast you'd need to skim to fill up the tanks.

G.

 

[DFW]

Who says scooping is done at an altitude where the pressure is anywhere near 1 atm?

Work out pressure on hull while travelling at hyper-sonic speeds. ALSO, work out the PSI on the hull when hit by MBT rounds that don't even scratch the paint on a Trav star ship WHILE not causing any leaks of gases (which require much smaller spaces to seep through than H2O.)

Then, you'll have an idea of how much pressure they can take.

 

[steelbrok]

Some years ago I started using this system (based largely on TNE's FFS ideas of needing internal bracing to enable a ship to withstand acceleration)

for every 1G of thrust, a ship can safely submerge 10 metres.

SDBs (having neither large cargo spaces nor needing the large fuel tanks of starships) can triple these depths.
I have no particular justification for this SDB ruling but it seemed cool to give the SDBs this "U boat" potential and the lack of larger open spaces would seem to be better for withstanding pressures (though I claim no proper reference for this)

 

[phavoc]

I would do a handwavium on this and move on. Come up with a number you feel comfortable with, say a starship with an armorfactor of 0 can go 1000meters down, and for every armor factor above 1, add another 500/1000 meters of depth.

It's simple, makes as much sense as any other rule, and you are done.

 

[Hopeless]

This has been brought up before in other forums but it was so long ago (for me) I can't remember what the consensus was.
How deep can a normal starship submerge itself under water (normal earth atmosphere) approximately 32 feet per atmosphere (sorry, I'm not sure how that translates to meters, but it's somewhere between 9 and 10 meters?
For some reason I keep thinking around 3 atmospheres was the deepest for "normal" starship hulls to safely submerge under water.
Any rules from mongoose?

There was an episode of Andromeda on this very issue but that also involved depth charges and only one vacc suit for the 2 people aboard it was also the episode where Rommy the android avatar did her one simulant recovery of a Magog fighter if I remember rightly!

Submarines are designed for underwater use, spaceships not so much but depending on their means of propulsion might still be operational, exactly how deep however depends on what caused them to be submerged in the first place!

Hope that helps!

 

[GJD]

Who says scooping is done at an altitude where the pressure is anywhere near 1 atm?

Work out pressure on hull while travelling at hyper-sonic speeds. ALSO, work out the PSI on the hull when hit by MBT rounds that don't even scratch the paint on a Trav star ship WHILE not causing any leaks of gases (which require much smaller spaces to seep through than H2O.)

Then, you'll have an idea of how much pressure they can take.

An M1A2 can survive an MBT tank shell hit. Want to drive it to the bottom of the sea? That survivability is because of specialist materials and manufacturing designed to shrug off one type of damage. Even if it were sufficently water proof and the turbine et al would run under water, all those seals will eventually fail, and the hull shape is designed to deflect point damage, not all-round crush.

You are taking the armor rating to be a measure of indestructability against any and all environmental conditions, when, actually, it relates to how well the ship shrugs off point, directed damage.

Hull material strength does not equal structural strength.

G.

 

[rust]

I would do a handwavium on this and move on. Come up with a number you feel comfortable with, say a starship with an armorfactor of 0 can go 1000meters down, and for every armor factor above 1, add another 500/1000 meters of depth.

It's simple, makes as much sense as any other rule, and you are done.

Yep. It is simply impossible to determine a realistic crush depth with the
data available within the Traveller framework, you would probably have
to use something like GURPS Vehicles or GURPS Under Pressure to get
anywhere close to reliable data, and it does not make much sense to do
this for a single adventure.

We plan on staying submerged until we pick up a distress signal on a predetermined setting.

If you intend to stay submerged you have certainly designed something
enabling you to receive the agent's signal, as you will not be able to re-
ceive a normal radio signal while under water ?

 

[DFW]

Even if it were sufficently water proof and the turbine et al would run under water, .

??? What ARE you talking about? What turbines?

You need to understand that pressure is pressure regardless of whether it is gas or liquid. The are the same in that respect.

 

[GJD]

Even if it were sufficently water proof and the turbine et al would run under water, .

??? What ARE you talking about? What turbines?

You need to understand that pressure is pressure regardless of whether it is gas or liquid. The are the same in that respect.

I don't believe I ever said they were any different, but I did say skimming at 0.1atm would be different from skimming at 1 atm.

The gas turbine was a throw away comment. I was referring to the gas turbine in the M1A2 in my example of why driving a tank to the bottom of the sea is a Bad Thing. I was trying to be facetious, as obviously an M1A2 won't drive under water (except with a fording kit, I suppose – but not to the bottom of the sea). My point was, gas turbines aside, that the design of a tank to resist being shot at does not make it a good design for resisting the crushing depths of the sea.

I know how pressure works. The point I was making is that your corollary between a ship being able to skim fuel at hypersonic speeds and being able to sit at the bottom of the ocean and shrug off a main battle tank gun hit because it has high structure and/or armour is fallacious. One does not automatically mean the other.

The stresses and pressures exerted on a ship during re-entry or during skimming are totally different to the pressures and stresses from sitting on the sea bed under a significant column of water, and different again from being shot at by a tank. That’s why when you look at a tank, a submarine and a re-entry vehicle, they look different and are built in different ways – form follows function.

The MGT starship statblock is not detailed enough to assume that because a ship can shrug of a tank gun hit it can resist 600 atmospheres of pressure at the bottom of the ocean.

G.

 

[DFW]

My point was, gas turbines aside, that the design of a tank to resist being shot at does not make it a good design for resisting the crushing depths of the sea.G.

Irrelevant. Tanks aren't designed as sealed, pressurized hulls and be pounded by weapons 100X as powerful as 120mm shells while STILL maintaining pressure integrity. Star ships are.

 

[Liam Devlin]

Jak Nazryth said:

Since there appears to be nothing in the rules, here are two "simple stupid" ideas I would like comments on.
Unless specifically designed as a submersible, a standard starship can submerge based on the following.

proposed rule 1 TL + Armor rating in atmospheres of depth
proposed rule 2 half TL + Armor rating in atmospheres of depth

So or TL 12 scout with 4 points of armor can either dive down to 16 atmospheres or 10 atmospheres in depth.

Any comments?

Mssr Jak,

TL+ Armor (rule1) gets my vote. Less math, and simplest way to explain it.

 

[rust]

Tanks aren't designed as sealed, pressurized hulls and be pounded by weapons 100X as powerful as 120mm shells while STILL maintaining pressure integrity. Star ships are.

Yep, but starships are not designed to suffer such hits constantly and over
every square centimeter of their entire hull at the same time. The fact
that an armour does withstand dozens of such hits does not ensure that it
will withstand that stress hour after hour. Besides, armour is not identical
to the structural frame of the vehicle, so I would not trust a starship hull
to automatically have the structural integrity of a submarine hull, especial-
ly if the starship's configuration is far from a sphere or cylinder.

 

[GJD]

My point was, gas turbines aside, that the design of a tank to resist being shot at does not make it a good design for resisting the crushing depths of the sea.G.

Irrelevant. Tanks aren't designed as sealed, pressurized hulls and be pounded by weapons 100X as powerful as 120mm shells while STILL maintaining pressure integrity. Star ships are.

Well, entierly relevant, I think. You said:

Work out pressure on hull while travelling at hyper-sonic speeds. ALSO, work out the PSI on the hull when hit by MBT rounds that don't even scratch the paint on a Trav star ship WHILE not causing any leaks of gases

The two are NOT the same. You are comparing apples and oranges. Efficent hull material that can resist tank shots (and more) does not mean that the vessel won't be crushed like a bug when all the seams, seals, welds and flanges fail.

G.

 

[far-trader]

Jak Nazryth said:

Since there appears to be nothing in the rules, here are two "simple stupid" ideas I would like comments on.
Unless specifically designed as a submersible, a standard starship can submerge based on the following.

proposed rule 1 TL + Armor rating in atmospheres of depth
proposed rule 2 half TL + Armor rating in atmospheres of depth

So or TL 12 scout with 4 points of armor can either dive down to 16 atmospheres or 10 atmospheres in depth.

Any comments?

Mssr Jak,

TL+ Armor (rule1) gets my vote. Less math, and simplest way to explain it.

I agree with Liam, sounds like a good rule of thumb to me. Simple, easy to figure, and reasonable. All I'd add is to make that operational depth.

For depth figures you can approximate 10m per atmosphere of pressure for Earth standard size and atmo. That gives the typical MgT ships (TL12 iirc) an operational depth of 120m.

For crush depth, to keep things spicy for the players, roll 2D6-2 for a percentage of additional depth. For example, your TL12 Armour 4 Scout above with a 16Atm rating has an operational depth of 160m. The secret roll of 2D6-2 comes up as 4, so 40% of 160 is 64. The crush depth is 224m. Let the players decide how far beyond 160m they want to go, with damaged systems and leaks, creaks and groans, all the way until they go beyond 224m and the hull fails catastrophically.

For greater depths the ship will have to be specifically designed as a submersible (a new hull designation and design sequence imo). The rules are for making spaceships, NOT submarines. And despite some comparisons they are worlds apart to a greater degree.

 

[far-trader]

For what it's worth to the discussion and your eventual house rule Jak I've tracked down some past published specs:

CT Adventure 12 ( pg 18 ):

Commercial vessels (traders, merchants, liners) can withstand up to 1,000° K and up to 1,000 atmospheres. Military vessels can handle temperatures to 1,500° K and pressures to 2,000 atmospheres. System defense boats are specifically constructed to handle temperatures to 2,500° K and pressures to 3,000 atmospheres. <copyright Game Designers' Workshop, Inc.>

Note however that those numbers are frankly (imo) excessive. The deepest ocean trenches on a large world are in the range of 10,000m. Using the above all ships are good to that depth and military and SDBs can go deeper. Seems kind of pointless to have that kind of excess built in. Personally I'd divide that by 10 and still be happy with it for an operational depth rating.

 

[SSWarlock]

My quick and dirty rule would be:

(Hull Armor + 1) * Surface Gravity * 1000 m = Crush Depth


Note:
IMTU the outer airlock doors are armored to the same level as the hull.

Let me know if this seems about right to you.

After reading some of the replies, perhaps this may be more realistic:

(Hull Armor + 1) * Surface Gravity * 500 m = Crush Depth

I like the idea of incorporating a world's Surface Gravity in the formula so that it can be used for both underliquid situations and in gas giant atmos. I am confused on one bit though. The way the formula reads now, it seems to be that the higher the Surface Gravity, the deeper the Crush Depth.

For example, a merchant with armor of 0 on a heavy gravity planet of, say, 2 Gs derives its Crush Depth as:

CD = (0 + 1) * 2 * 500 m = 1000 m

On a 1G world, its CD = (0 +1) * 1 * 500 m or 500 m.

Shouldn't the formula evaluate so that the higher the Surface Gravity, the shallower the Crush Depth? That is,

(Hull Armor + 1) / Surface Gravity * 500 m = Crush Depth

If not, what am I missing?

Also, how can Structure be incorporated into the formula? Doesn't deliberately buffing a ship's structure above the "standard" for a given displacement mean the structure can take more punishment without catastrophic failure?

 

[Jak Nazryth]

I would do a handwavium on this and move on. Come up with a number you feel comfortable with, say a starship with an armorfactor of 0 can go 1000meters down, and for every armor factor above 1, add another 500/1000 meters of depth.

It's simple, makes as much sense as any other rule, and you are done.

Yep. It is simply impossible to determine a realistic crush depth with the
data available within the Traveller framework, you would probably have
to use something like GURPS Vehicles or GURPS Under Pressure to get
anywhere close to reliable data, and it does not make much sense to do
this for a single adventure.

We plan on staying submerged until we pick up a distress signal on a predetermined setting.

If you intend to stay submerged you have certainly designed something
enabling you to receive the agent's signal, as you will not be able to re-ceive a normal radio signal while under water ?

I am brand new to the party. The group has already had 5 or 6 game sessions by the time I joined. After we submerged the scout ship, one of the other players said... "We'll pop a communication buoy and listen at depth." The GM agreed, so being brand new to the group, I didn't say anything. (I refues to interupt a game questioning the GM's every move unless there is an OBVIOUS error in the game mechanics)
All I know about the ship is that it's a heavily modified type S scout and the GM uses WARP drives instead of Jump Drives (warp out of the core rule book). This scout ship also has a 20 ton module that is normally installed with a cargo module, but the government the group is working for has placed it's own spy-module into the ship. It has it's own crew, air raft bay, sensory equipment, etc... so I guess the "buoy" came for the "spy module"... I am an architect and geek out on deck plans, so I did a quick sketch with a couple of plans and sections the GM and players agreed on.
That's about all that happened. Kinda boring game but I'll give it one more chance, otherwise I can think of better ways to spend a Saturday afternoon.

 

[rust]

After we submerged the scout ship, one of the other players said... "We'll pop a communication buoy and listen at depth."

That is good enough, the buoy could for example send a sonic signal to
the submerged scout ship when it receives the radio signal.

I hope the game gets more interesting for you.

 

[rust]

Note however that those numbers are frankly (imo) excessive.

Looking at starships designed with the at least remotely realistic GURPS
system, the data for Traveller starships look more like this:

Dragon Class SDB: crush depth 1,790 yards
Wyrm Class SDB: crush depth 8,180 yards
Sea Animal Class Aquatic Safari Ship: crush depth 290 yards

The average for civilian ships is there between 200 and 300 yards.

 

[rust]

Also, how can Structure be incorporated into the formula?

The way most elaborate design systems do this is a "fudge factor" which
depends on the strength of the structural frame, for example crush depth
x 1/2 for a light frame, x 1 for an average frame, x 2 for a heavy frame.

By the way, configuration would also be very important. A sphere is basi-
cally more pressure resistant than a box.