How Deep Can I Go?

[Jak Nazryth]

I purchased adventure 3, The Calixcuel Incident, and it describes starships making poor submarines for various reasons...

To quote from page 3 from the adventure.. "A starship will typically need to resist a pressure differential of one atmosphere, though most can tolerate quite a bit more; stopping one atmosphere of pressure from getting out into a vacuum is a lot different to stopping ten atmospheres from getting in."

The submerged city, or portions of it, are more than 110 atmospheres of pressure.
I am using this adventure as one of several plot hooks (I generally let my players pick from a group of possible adventures) and if my players pick it, I want to make sure I'm on solid ground if (and most likely "when") they argue that they can simply submerge their far trader (or which ever ship they end up buying) down deep and dock with the city. Obviously the easy answer is that starship airlocks are not designed to dock under water, not to mention normal star ship sensors aren't designed to work under water.

But this got me to thinking.
How deep can a typical starship go? What is the crush depth?
Sure, the hull might be strong enough to take quite a bit of pressure, but what about the seals of hatches, cargo doors, iris valves, landing gear wells, and most obviously "windows" (like on most bridges and cockpits) be it "trasnpersteel" or what ever Traveller view ports are made of.
Does armor and reinforced hulls help with crush depth and if so, by how much?

It is a pretty common theme for a starship to crash land on a planet, but what if it crashes into an ocean and sinks? How deep can it sink before..."blurp" implosion where every living thing is crushed in a millisecond? Calixcuel got me thinking a lot of what can happen on a water world... a rescue mission in deep water perhaps?

I also just picked up High Guard, but I've only just started reading it.
Is the answer there?

Thanks.

Jak

 

[PsiTraveller]

The answer is not in Highguard. As for the depth you can go, the answer I think you will get is, as deep as the plot needs you to. I don't think there are any rules in the game for crush depth.

You could guesstimate from crush depths for modern submarines https://en.wikipedia.org/wiki/Submarine_depth_ratings but then you have to add in Traveller Armour and TL improvements as well as wondering if the gravitic systems can aid in any way (as a plot device for example).

Hope this helps

 

[Jak Nazryth]

Yeah, in the new High Guard I read the paragraphs describing the variants in Starship hulls, high pressure / under water was not one of them.
While walking my dog, I kept thinking about it and came up with a very simple answer.

Here is my simple rule of thumb for a rarely used situation...

Atmosphere pressure = Tech Level

A TL 10 ship can safely withstand 10 atmospheres of pressure and remain "operational". A TL 12 ship can withstand 12 atmospheres of pressure and so on.
Granted... the airlocks and seals are more important at this point. Not sure if a standard airlock can even cycle liquid water unless specifically designed.. (If the party wants to venture outside the ship in shallow depths in standard vacc suites)
2x TL is when major damage starts to occur, water starts to intrude, view ports start to develop cracks.... Last time I checked starships were not designed to pump out water...
Absolute depth or crush depth is 3 times TL.
This can also works for gas giants and other High Pressure atmosphere worlds.
Again, this only has to do with a standard starship, or ships boat/fighter, etc... craft designed for depth can go as deep as the plot allows.

I now recall this question coming up a few years ago... somebody actually calculated the following... since a hull can take "x" amount of damage from a starship weapon, and a point of armor can withstand "x+X" amount of damage... he somehow "ran the numbers" and proved "mathematically" that a hull could withstand thousands of atmospheres of pressure under water based on the structural integrity of 1 square centimeter of bonded superdense...
I don't really feel like "doing the math" in many cases. But even if the math is true on a sci-fi material, it doesn't deal with typical seals, hatches, openings, view ports/windows, etc...

I want a simple rule of thumb. I love many aspects of the "hard science" part of Traveller, but at some point we need to keep it a fun sci-fi RPG instead of a reality simulator.

Anyway, I know Matthew Sprange and the rest of the Mongoose writers have a 1001 issues every day to consider in revamping the rules. This can be issue number 1002.

 

[Condottiere]

I'd use armour and hull configuration as the basis.

 

[Jak Nazryth]

Condottier, you make a good point.
You can simply add any points of armor to the base TL of a hull and get atmospheres of pressure.
A TL 12 starship with 4 points of armor (no matter what type it is) will equal 16 atmospheres of pressure a normal starship can withstand before the hull/seals begins to fail, and 48 atmospheres = instant death.
I'm inclined not to care about the configuration of the hull, cylinder, sphere, shoe-box, etc... sure a sphere is better a distributing high pressure across it's surface than a cube, but I'm just going to keep a basic rule of thumb.
Good points though.

 

[Spartan159]

Just how much pressure is there at Gas Giant scooping depths?

 

[Jeraa]

Just how much pressure is there at Gas Giant scooping depths?

According to GURPS Traveller: Starships, you are above cloud level when skimming, and the density and pressure are only at 0.1 atmospheres or less.

 

[locarno24]

Secrets of the ancients had a gas giant depth/pressure damage table in one of the missions. Might be worth looking there if you can find a copy.

 

[Jeraa]

Secrets of the ancients had a gas giant depth/pressure damage table in one of the missions. Might be worth looking there if you can find a copy.

Doesn't seem to be in the Mongoose version. The CT version says commercial ships can survive up to 1,000 atmospheres, military vessels up to 2000, and system defense boats up to 3000. It also says pressure at skimming level is usually no more than 0.5 atmospheres.

On Earth, water pressure is 1 atmosphere per 10 meters of depth. With the CT numbers, that puts the limit at 10,000 meters (33,000 feet) for commercial ships. The deepest part of our ocean is at 11,034 meters. So a commercial vessel (from a MgT point of view, an unarmored ship) could survive most the entirety of the Earths ocean depth.

Basically with CT numbers, a starship can co to the bottom in most cases. High gravity worlds and worlds with particularly deep oceans would be different.

Edit: No, wait. The Mongoose version does have something about the pressure. I missed it.

Further Edit: While the 2e version doesn't mention it, the 1e version of the hostile environment suit (TL 8, core rulebook 1e, page 87) says it protects from high pressure environments, like deep sea trenches. If a suit of personal armor can protect from that, I would have to assume something as strong as a starship would be fine at such depths as well.

 

[MongooseMatt]

Anyway, I know Matthew Sprange and the rest of the Mongoose writers have a 1001 issues every day to consider in revamping the rules. This can be issue number 1002.

I think we can do this one quickly

This is an excerpt from a forthcoming book:




Almost all starships can survive being submerged in shallow water, but this does not equate to operating underwater in an effective manner. Under normal conditions, a starship is in vacuum with an internal pressure not much greater than one atmosphere, and is designed to keep air in at this pressure differential. There is a large margin of safety built into most ship designs, but there is a huge difference between keeping air in and keeping high-pressure fluids out.

One atmosphere of pressure is encountered on an Earth-mass world at a depth of just ten metres below the surface. This is in addition to the normal atmospheric pressure of the world. A starship can easily withstand this of course, even though its seals are designed to work in the opposite direction. Five atmospheres should not be much of a problem for most ships, but this is encountered just 50 metres down.

The Harrier is about 40 metres long. Should she somehow end up standing on her tail in water, the pressure on her cargo doors would be about four atmospheres greater than on her avionics access hatch. This situation is unlikely to arise (though, with Travellers, who knows…) but it does illustrate the rapid increase in water pressure at depth.

By way of comparison, the average depth of water over the continental shelf on Earth is about 60 metres, but can be as much as 150 metres. Few starships can operate at depths of more than 50 metres without starting to leak a little, but this is generally tolerable for a period; at 100 metres down the leaks will be serious. Crush depth is much greater, but operating a highly complex vehicle filled with electronic components with water entering at various points is a recipe for disaster. However, there are occasions when operating in deep water is desirable or necessary.

The usual reason for entering deep water is to hide. System defence boats and raiders both use this practice to good effect, and are often modified to permit such operations without undue hazard. The Harrier can be partially or fully configured for underwater operations. Partial modification permits operations down to a depth of 300 metres without hazard, and also installs an underwater manoeuvring system. This is a modification of the ship’s fuel scoop system which is fitted with a powerful pump and exhaust capable of driving the ship at 10 knots underwater (equivalent to Idle speed). Small fins provide guidance, and compartments within the fuel tanks can be used to trim and ballast the vessel. This comes at the cost of 2 Structural RU and 2 Technical RU, plus 2 Cosmetic RU if appearances are to be maintained, and takes up 2 tons of cargo space for extra machinery.

Partial modification is entirely sufficient for operations on the continental shelves of most worlds and along their fringes. Full modification is more comprehensive, permitting operations down to 1000 metres. The average depth of Earth’s oceans is around 3500 metres, but those of many worlds are shallower and, in any case, there will usually be seamounts or shallower areas where a modified starship can ‘land’. Full modification also includes a more powerful drive system capable of 20 knots underwater (equivalent to Very Slow speed) plus a bank of powerful lights and specialised underwater sensors. Airlocks are also strengthened to allow the use of deep-diving suits should the Travellers wish to go outside. Full underwater modification costs 5 Structural RU and 3 Technical RU plus 4 Cosmetic RU if appearances are to be maintained. In addition, 6 tons of cargo space are also consumed.

If any underwater modifications are made and an atmospheric manoeuvre kit is also installed, the DM on Pilot checks applies when operating in any fluid medium.

 

[locarno24]

Looks interesting.

This situation is unlikely to arise (though, with Travellers, who knows…)

In no way do I admit to having accidentally sunk the Harrier before.
And besides, how was I supposed to know that the beacon we were locked onto when coming in to Raft wasn't actually the one on the pad?

At the same time, a simple set of rules for sub-capable operations is nice. Even if I am now picturing Skydiver One.

 

[AnotherDilbert]

The Harrier can be partially or fully configured for underwater operations. Partial modification permits operations down to a depth of 300 metres without hazard, and also installs an underwater manoeuvring system. This is a modification of the ship’s fuel scoop system which is fitted with a powerful pump and exhaust capable of driving the ship at 10 knots underwater (equivalent to Idle speed). Small fins provide guidance, and compartments within the fuel tanks can be used to trim and ballast the vessel.

Why would we need a secondary drive system? Wouldn't the Manoeuvre drive work underwater just as well as anywhere else?

 

[phavoc]

A TL 10 ship can safely withstand 10 atmospheres of pressure and remain "operational". A TL 12 ship can withstand 12 atmospheres of pressure and so on.
Granted... the airlocks and seals are more important at this point. Not sure if a standard airlock can even cycle liquid water unless specifically designed.. (If the party wants to venture outside the ship in shallow depths in standard vacc suites)
2x TL is when major damage starts to occur, water starts to intrude, view ports start to develop cracks.... Last time I checked starships were not designed to pump out water...
Absolute depth or crush depth is 3 times TL.
This can also works for gas giants and other High Pressure atmosphere worlds.
Again, this only has to do with a standard starship, or ships boat/fighter, etc... craft designed for depth can go as deep as the plot allows.

Generally speaking you are correct. An 'air' lock designed for space is not equipped to be a 'wet' lock. Not that it couldn't, but the effort required to pressurize and depressurize a liquid vs. atmospheric environment are different and should be treated as such.

And yeah, starships aren't designed with bilge pumps.

 

[locarno24]

The Harrier can be partially or fully configured for underwater operations. Partial modification permits operations down to a depth of 300 metres without hazard, and also installs an underwater manoeuvring system. This is a modification of the ship’s fuel scoop system which is fitted with a powerful pump and exhaust capable of driving the ship at 10 knots underwater (equivalent to Idle speed). Small fins provide guidance, and compartments within the fuel tanks can be used to trim and ballast the vessel.

Why would we need a secondary drive system? Wouldn't the Manoeuvre drive work underwater just as well as anywhere else?

Simply applying a force to the ship, yes. But I'm not sure what sort of wierd grav effects might apply to the near-drive-plate area outside the ship, and what sort of turbulence that'd produce in a dense liquid. Plus, I'm not sure how much heat you'd be trying to dump from the M-drive heat sinks. Probably not enough to boil water at any depth, but maybe, and cavitation can do nasty things to seals and joints.

 

[Jak Nazryth]

Thanks for all the input.
This will give me "Cannon" guidance.
Also, I kind of agree with the proposal that a reaction-less drive / grav plates, should be able to maneuver a ship under water, just much less efficiently.
I'll just give it a .1 normal thrust rating. So at this point a ship CAN operate under water and now I have concrete answers on "how deep", but the airlocks cycling under water will still be an issue unless the players FIRST make modifications per Mathew's post.
Jak

 

[hivemindx]

Contrary to a previous poster I think the hull profile is far more important than the armour rating. I don't think the amount of heavy armour designed to prevent damage inflicted by weapons necessarily relates to the amount of pressure the hull can take. However I think we can assume that am armoured ship is probably built to somewhat higher tolerances across the board and so long as the hull is a good shape it should withstand pressure better than an unarmoured ship.

I don't see why the airlocks wouldn't work perfectly well when docking with another vessel or an underwater city. If the other side of the lock is at normal pressure then it should work just as well as normal. Yes there is a huge amount of pressure on the seal but if we are assuming that water isn't bursting in through every hatch in the hull we should assume that the airlock seals work just as well. I agree that if you want to go out in to the water the lock may have a big problem.

There is a not really relevant but related and very interesting What If about using a submarine on Jupiter. It talks about the fairly confusing difference between atmospheric pressure and density.
https://what-if.xkcd.com/138/

 

[legozhodani]

Interesting link, thanks. :idea:

 

[phavoc]

Contrary to a previous poster I think the hull profile is far more important than the armour rating. I don't think the amount of heavy armour designed to prevent damage inflicted by weapons necessarily relates to the amount of pressure the hull can take. However I think we can assume that am armoured ship is probably built to somewhat higher tolerances across the board and so long as the hull is a good shape it should withstand pressure better than an unarmoured ship.

I don't see why the airlocks wouldn't work perfectly well when docking with another vessel or an underwater city. If the other side of the lock is at normal pressure then it should work just as well as normal. Yes there is a huge amount of pressure on the seal but if we are assuming that water isn't bursting in through every hatch in the hull we should assume that the airlock seals work just as well. I agree that if you want to go out in to the water the lock may have a big problem.

There is a not really relevant but related and very interesting What If about using a submarine on Jupiter. It talks about the fairly confusing difference between atmospheric pressure and density.
https://what-if.xkcd.com/138/

That's correct - the amount of armor you have isn't necessarily a good way to resist pressure. If you don't have the proper engineering to handle the pressure your uber armor will still collapse on itself. That's basic engineering. It's also why you see circular hulls for submarines. During WW2 the hulls were not circular and while the engineering wasn't the same as it was later, the hulls still had an upper limit on what they could accept. Plus the hull forms were optimized for faster surface running whereas modern submersibles are designed for faster undersea running.

The Trieste went to the bottom of the Mariana's trench and it's non-human compartments were NOT spherical, then again they were not meant to hold a human. The lower sphere that housed the operator was spherical to withstand the great pressures.

Airlocks could work underwater with proper seals, but they are not designed, generally, to pump water out, especially water at greater pressures than normal. The machinery for draining liquid is different than atmosphere. Though one might argue that a vacuum-rated seal is totally useless under more than a few atmospheres. The pressures would simply collapse a standard seal.

 

[Condottiere]

Use the multi environment space option.