Is there an upper limit to streamlined hull displacement?

[Black Vulmea]

Just as it says on the tin: are there limitations in any of the various Traveller rules iterations on hull tonnage for streamlined ships capable of operating in atmosphere?

Can, say, a 500 kdt streamlined starship land on a planet with a standard or dense atmosphere? Can it skim fuel from a gas giant?

 

[robject]

I just assumed that High Guard sets a limit, but on retrospect, I think it doesn't. I know I always had a limit in my own mind, but I think Traveller does not.

 

[Carlobrand]

No limit is stated in High Guard, nor is there a limit in MegaTraveller. The 30,000 dTon Gionetti class light cruiser of Supplement 9 is streamlined. MegaTrav's BI13 dreadnought of Fighting Ships of the Shattered Imperium is streamlined at 700,000 dTons. The Fifth Frontier War boardgame features streamlined Sword Worlds dreadnoughts.

Add: Do note that the Azhanti High Lightning boardgame defines some consequences to that ship refueling by skimming. Supplement 5 states that there is a chance one or more fuel shuttles, which are exterior-mounted, will break free due to atmospheric turbulence during the process. Supplement 5 also states there is a chance of damage to a fuel deck due to buffeting with resulting loss of fuel from that deck. That might be a problem unique to the AHL or one that just occurs to partially streamlined ships or maybe just to capital ships. Always seemed odd to me.

 

[Travellerspud]

the real issue, I would think, would be where do the big ships land, besides water? (without the landing gears punching through the surface due to weight)

IMTU I picked 1000 dTons as the largest that most Starports could handle, and 400 dTons what the average planetary surface unimproved could handle (larger ships either landing in water or in special cradles).

 

[GypsyComet]

CT made a statement as to the largest ships that could land, but that is only part of the benefit of streamlining. The big military ships will, in frontier cases, need to refuel themselves or have a big tanker be able to perform the same task. That means dipping from gas giants, an operation which is safest in a streamlined hull.

Some editions also add an "airframe" option.

The steps in streamlining essentially work out to the following:
-Airframe means you don't have to use the drives to steer, just to keep moving.
-Streamlined means you don't have anything stuck on the outside that will rip off in air.
-Partially Streamlined uses the Streamlined definition, but adds the word "mostly".
-Unstreamlined means you treat air heavy enough to show on sensors with the utmost respect by either staying out of it or having the engines, duration, and intestinal fortitude to match velocities with any air mass you try to move through, and accepting that you'll be doing an antenna, wiper blade, and turret inventory afterwards. You may also need a specific cradle to land, or just keep your gravs running the whole time so you don't actually touch the ground, since the ship may not have been designed with landing gear.

 

[McPerth]

See that most capital ships (tenders excluded) are streamlined just because its configuration is so, even if only as defense against meson attack. That does not mean they can enter into atmosphere, where other things must be taken into accoutn too (not less of wich is the gravity wells).

As I used it (not sure if I read it or just I assumed), there is a limit for ships to land (regardless of configuration). See that Naval Bases have on ground capacities for ships up to 1000 dtons, larger ones being served at orbit (MT:IE page 32, under Naval Base, among other sources). That's the limit I always used for ships that can routinely land, larger ones being able to but the operation is risky (and over 5000 dtons very risky, if posible at all) due to sheer size (after all, a 1000 dtons is about the size of a WWII cruiser, and a 5000 stons about that of a battleship or carrier, and in both cases, acording to MT rules, quite more dense, and so, heavy). And imagine the presure their landing gear would have to support...

As for skimming, I'm not so sure, but I guess maneuvering in atmosphere (and with strong gravity wells) with too large a ship would be risky at least, so only used as exceptional ressort.

 

[Selandia]

the real issue, I would think, would be where do the big ships land, besides water? (without the landing gears punching through the surface due to weight)

IMTU I picked 1000 dTons as the largest that most Starports could handle, and 400 dTons what the average planetary surface unimproved could handle (larger ships either landing in water or in special cradles).

Beside the structural challenge of a 1,000,000 dton doing a three point stand to start with

T5 postulate the use of lifters (p.307) thus solving the weight issue and T5 explicitly pose no limitation to streamlining.

have fun

Selandia

 

[McPerth]

Afterthoughts...

A comment in another thread reminded me about the K'kree 6000 dtons Xeekr'kir merchant, that was expected to land, as the K'kree don't fit well in small crafts (in Challenge 28 it was said they are boarded by a ramp, so directly from ground), so hinting that ships larger than what I thought can also land.

Maybe the K'kree, due to their clustrophobia (that makes them to build large ships and to land them to avoid the use of shuttles) build them stronger to overcome the landing problems for those battleship size starships...

 

[GypsyComet]

It can also be seen as a practical limit of starports. Streamlined forms get very long very quickly, and you run out of real estate awfully fast when you have to design every landing bay for 200m long arrowforms.

As a benchmark, nothing we have flying today (other than one-use heavy lifters) is more voluminous than a Type R.

 

[Timerover51]

It is possible to drydock a 160,000 ton cruise ship, if you have a dry dock that can take the weight, and also set up the dry docking blocks very carefully. That would equate to a Traveller ship of about 11,500 dTons. Note, those ships are over 350 meters long and 40-45 meters in beam, and would be viewed as "small" in a Big-Ship Traveller Universe. That would be the closest Real World analogy to landing a large streamlined ship.

With a streamlined 310,500 dTon Traveller ship, you might be looking at a ship that is over One kilometer long and 150 meters in beam. Shorten the ship, increase the beam. All that mass means the entire bottom of the ship is your landing surface, and what it lands on had better be really solid, either bedrock or a meter or so of GOOD reinforced concrete, or you are using your lifter drive continuously while down. That does make it a bit hard to shut it down for maintenance.

That is one of the reasons I am a Small-Ship universe guy. One of the big Lake "footers", so-called because they are 1,000 feet long (305 meters), would only equate to about an 8,000 Traveller dTon ship. The big Lake boats can haul 70,000 tons or so of iron ore, coal, limestone, grain, etc., assuming Lake levels are about normal, which they are presently, and still going up. That is a LOT of cargo, although is it bulk-loaded, and not containers.

A WW2 Liberty Ship was listed as having a gross tonnage of 7,191, and a deadweight tonnage of 10,828. A gross ton is a measurement of internal volume, representing 100 cubic feet, so figuring a Traveller dTon at about 500 cubic feet, there would are 5 gross tons per dTon. That would make a Liberty equivalent to a 1440 Ton Traveller ship. That 7191 gross tons does include the engine and boilers, crew quarters, superstructure, so everything internal to the ship. That is not just cargo space.

Deadweight tonnage is the total tonnage of cargo that can be carried safely, but does include fuel, crew, passengers, and stores. When you add that to the light weight of the Liberty, you get around 14,000 or so tons of loaded ship. A Liberty is 441.5 feet long, beam of just under 57 feet, and hull is about 42 keel to top deck. Now think, that is only a 1440 dTon Traveller ship. If you double all of those dimensions, you get a ship of only 11,520 dTons Traveller. In the Real World, that is a big ship. In the Traveller large ship universe, it is a midget.

 

[rancke]

That is one of the reasons I am a Small-Ship universe guy. One of the big Lake "footers", so-called because they are 1,000 feet long (305 meters), would only equate to about an 8,000 Traveller dTon ship. The big Lake boats can haul 70,000 tons or so of iron ore, coal, limestone, grain, etc., assuming Lake levels are about normal, which they are presently, and still going up. That is a LOT of cargo, although is it bulk-loaded, and not containers.

But it's as nothing compared to the amount of goods that billions of people can produce.

Deadweight tonnage is the total tonnage of cargo that can be carried safely, but does include fuel, crew, passengers, and stores. When you add that to the light weight of the Liberty, you get around 14,000 or so tons of loaded ship. A Liberty is 441.5 feet long, beam of just under 57 feet, and hull is about 42 keel to top deck. Now think, that is only a 1440 dTon Traveller ship. If you double all of those dimensions, you get a ship of only 11,520 dTons Traveller. In the Real World, that is a big ship. In the Traveller large ship universe, it is a midget.

10,000dT is a decent-sized ship in the Third Imperium setting.

Mind you, I don't see the big cargo haulers and passenger liners landing on the surface of worlds.


Hans

 

[Carlobrand]

CT made a statement as to the largest ships that could land,...

Did it? I don't recall such a statement.

... or just keep your gravs running the whole time so you don't actually touch the ground, ...

In the MegaTraveller system, which is one that does the airframe thing, you'd need to make sure you actually installed gravs. Otherwise it's just you and that maneuver drive.

See that most capital ships (tenders excluded) are streamlined ...

Most canon CT capital ships are partially streamlined. Most canon MegaTrav capital ships are streamlined. I don't know how the rest handle it.

...That does not mean they can enter into atmosphere ...

And it does not mean they can't. Unless someone knows somewhere that specifically says one way or the other, it seems to be left up to the preference of the game master.

And, to make matters more complicated, CT Adventure 7, Broadsword, has the Broadsword "grounding" on Garda Vilis, a size 9 world with a standard (tainted) atmosphere, yet the very same book describes the ship as, "unstreamlined, although it has sufficient lack of projections to allow it to skim hydrogen from gas giants in order to refuel." In other words, partially streamlined. The adventure goes on to say, "It may land on vacuum worlds, but generally interacts with the surfaces of worlds through its complement of 50-ton cutters, their interchangeable modules, and the ship's single air/raft." Broadsword is no capital ship, but it also is very much not streamlined, at least according to the adventure that features it. So, apparently there's some ability to "ground," as distinguished from atmospheric flight. Note also that there's no mention of damage during skimming.

 

[GypsyComet]

Did it? I don't recall such a statement.

More of an implication that ports were rarely built to handle larger ships, now that I slow down to look it up. It isn't in the rulebooks, but in the description of Champa Starport in JTAS 7. A class A port on a high population world in a busy sector (the Solomani Rim), Champa Downport is described as having landing pads that can handle up to 400 tons, with anything larger assumed to have its needs met better in orbit.

As such it is a setting "rule of thumb", not an actual rule.

 

[Timerover51]

I did some number crunching, using the dimensions of the World War 2 Liberty Ship as the basis for a 1440 Traveller dTon ship, and then allowing for a block coefficient of 0.75 for some streamlining for atmospheric landing. Block coefficient is the ratio of the volume of a ship verses the volume of imaginary block of water of the same length and beam dimensions of a vessel. For a cargo ship, that will generally run about 0.75, for a destroyer possibly as low a 0,50, and for ships with substantial underwater blisters, it could be greater than 1, as block coefficient is based on the beam at the waterline.

Basically, mixing metric and Imperial units, what you get is about 18,000 square feet of ship's bottom bearing on the landing surface, and if you assume 5 metric tons cargo of ship's mass per Traveller dTon, you get 7200 metric tons on that 18,000 square feet. That gives you a live load of 400 kilograms or 882 pounds per square foot of landing surface. A parking garage is built to handle a live load of 125 pounds per square foot of parking surface, and I think that you know how thick the floors of parking garages are. Landing a small, in a Big-Ship Universe, 1440 dTon freighter, with dimensions similar to a Liberty Ship, is going to put roughly 7 times the load on the landing surface than a parking garage is designed to handle.

Based on that, even for a 1440 dTon freighter, you are going to need a meter or so of high-quality reinforced concrete or solid bedrock to land on. For very large ships, like some of your 100,000 dTon battleships or liners or bulk carriers, the mass verses load-bearing surface is going to be so high as to render landing them on a planet impossible without fairly elaborate landing arrangements being made, or the ship basically doing a "powered hover" at a designated spot.

Now, I figured the Liberty at about 42 feet from keel to top deck, with the superstructure added to that. You could reduce the vertical dimension by say a factor of 3 and triple the landing surface, but you are still going to exceed a 100 kilograms of weight per square foot, so you will still need a solid place to land on, or design the ship to make water landings. The water landing does not really help the very large Big-Ship Universe ships, as there you are starting to look at tons per square foot of bearing surface on land, or immersing a very large portion of the ship hull in water in order to float.

As a rule of thumb, I would say that it is going to be extremely difficult to land any streamlined ship of over about 5000 Traveller dTons without making the ship into what amounts to be a thin, flat pancake. Your very large spherical or other streamlined shapes are going to have to do a power hover, and not shut power plant or lifting engines down at all.

 

[Carlobrand]

More of an implication that ports were rarely built to handle larger ships, now that I slow down to look it up. It isn't in the rulebooks, but in the description of Champa Starport in JTAS 7. A class A port on a high population world in a busy sector (the Solomani Rim), Champa Downport is described as having landing pads that can handle up to 400 tons, with anything larger assumed to have its needs met better in orbit.

As such it is a setting "rule of thumb", not an actual rule.

Not that I'm saying your implication is wrong, but JTAS 7 is the same issue that releases part 2 and 3 of High Guard. There's a good chance that Champa wasn't written with High Guard in mind. Now, personally, I am of the opinion that you're better off putting your customs in orbit at the high port and letting the big freighters process through there, because that way the cargoes can de-orbit on shuttles and go more or less straight to the cities they're intended for, rather than having to drop down to the ground port and then push through the atmosphere to get there. However, I say again that there's nothing in canon to prevent some gamemaster from landing big streamlined ships on any given world.

...As a rule of thumb, I would say that it is going to be extremely difficult to land any streamlined ship of over about 5000 Traveller dTons without making the ship into what amounts to be a thin, flat pancake. ...

I disagree on the pancake bit, but I agree that designing a landing pad to support a ship as big and heavy as a skyscraper would be a challenging and expensive bit of engineering. I expect designing such a ship to fly through atmosphere and then land and support its own weight under gravity is no small feat either. Coupled with my above comment on the efficiency of high ports, I'd consider it unlikely that big ships would be landing on a routine basis. However, I do not rule it out. Among other things, in wartime it would be very useful for your business' ships to ground and shelter under the planetary defenses - maybe in the water - when the enemy shows up a'raiding. Lacking any specific mention in canon that says they can't, I'd be inclined to believe the ships are engineered to be able to do it if needed but, for practical reasons, generally don't.

Heck, with nukes and mesons flying about, I'd design the high port itself to be able to ground and hide in water.

 

[atpollard]

Given the traveller mechanics of Fusion PPs and Grav MD's, a super-ship need never land a single skid on the ground ... it can just hover for a week, and then lift off.

I suspect that the length/20 upper limit on slenderness will require some adjustment to some classic designs, but size is not a limiting factor.

 

[Carlobrand]

... the length/20 upper limit on slenderness ...

???

 

[atpollard]

???

Sorry, Engineers calculate to 4 decimal places ...
... Architects use empirical rules of thumb.

Any slender object, like a joist or a column, whose length exceeds 20 times its smallest dimension has a strong tendency to twist and buckle. In my world, that means that a 4"x4" wood column should be no taller than 4"x20=80"=6'8" (these are preliminary design guidelines, there are lots of final calculations that still need to be done).

What makes this useful, is that it works as an approximation for wood, steel, concrete ... all sorts of materials. Hollow or solid makes no difference either. Beyond a length of 20 diameters (or widths), objects become unstable.

Many starships are drawn only 3 decks tall and VERY long and wide.
With 3 decks as a minimum dimension (call it 9 meters tall), the maximum length is 180 meters ... beyond that the ship folds like a cheap umbrella.

 

[mike wightman]

Buildings don't include artificial gravity plates, acceleration compensation fields and magic 6g manoeuvre drives.

Traveller ships up to 1000000t (and bigger since there is no upper limit in HG2) can throw themselves around at 6g.

If they can withstand the forces of combat manoeuvring then they can easily manoeuvre inside an atmosphere if they are streamlined.

What happens if they switch off all the magic force field stuff when they are grounded is probably not nice though

 

[Carlobrand]

Buildings don't include artificial gravity plates, acceleration compensation fields and magic 6g manoeuvre drives. ...

None of which helps if you apply a significant external force perpendicular to the line of travel.