Canonically from classic Traveller the mass limit of a cargo ton is 1000kg.
I'm not doubting you, but that's redonkulous. In real world shipping, a TEU is up to 24000kg, depending on what is loaded with. And a TEU is a bit more than 2.5 dtons. A dton should be up to 8800kg based on real world shipping measures.

Well, let's see... A dton (13.5 cubic meters) of water masses 13500 kg (easy conversion; one cubic meter of water masses one metric ton). Anything with a greater density than water is going to mass proportionately more per displacement ton. So, for example, bulk building supplies could quite easily exceed 24000 kg per dton. (Typical density for construction bricks seems to center roughly on 1.8, and bricks stack extremely well, so you could reasonably pack a shipping container almost entirely full. At a density of 1.8, that yields 24,300 kg for 13.5 cubic meters.) (Structural steel, by comparison, has a density of almost 8, but probably can't be packed as tightly, probably yielding a shipping density closer to 3 - still yielding a higher shipping mass per displacement ton, but not nearly as bad as if you were shipping a solid block of steel.) In any case, I would say that the limit is considerably higher than that 8800 kg per dton estimate...

Yeah, you can put more weight in a container. But that's what's considered safe, though the actual limit is slightly higher. You could imagine high tech materials that are sturdier without being significantly more expensive. I'm just sticking with values we know for purposes of this discussion.

Your gantries and cranes and container hauling vehicles have to be able to handle the load, not just the literal volume.

At some point cargo and trade needs a closer look or overhaul. Since 'lots' are in 10, 5, and 1 dton increments, I've always thought of 5 dtons as a TEU (a twenty-foot container - which is very roughly 6 X 2.5 X 2.8 meters, or close enough to 8 squares. Unfortunately that's only 4 dtons, which is neither 5 dtons or the 'standard container' size of T5, which is 3 dtons. By the same TEU-like logic, 10 dtons is a 40-foot container and 1 dton is some weird shaped box or cargo flat that can be stacked.

Since Traveller (or TEUs) don't really deal with mass, I see no point in introducing mass, but the container size thing should be better coordinated to correspond to deck plans and assumed ceiling heights - and the existing trade/freight/mail rules. That identifies the problem, but doesn't provide an answer. I'd lean towards a 'standard' container of 4 X 2 squares (and just enough under 3 meters tall to account got a ceiling) equaling five 'shipment tons' as a simplifying expedient to avoid re-writing the speculative trade and freight rules, but I'm not sure if that compromise will make anyone happy. Of course, if everyone is equally unhappy, then it's a compromise solution...

Wouldn't depend on the strength of the container and it's materials?

If you used balsa wood as the flooring, I wouldn't be surprised if anything heavy breaks through.

Imagine that you have a pop 6 planet with a class B starport that, for reasons of geography or politics or whatever, needs to import 80% of its domestic consumption. So it is heavily involved in interstellar trade. Coincidentally, this closely mirrors the situation in Hawai'i, whose port I know well since I have to deal with it almost daily at my work.

That 80% of domestic consumption translates to 100,000 TEU per month. Since a TEU is approximately 2.5 dtons and we want to be extra sure to bring in everything we need, let's call that 10,000 dtons per day. How might this be solved?

One could imagine a system where a megafreighter like the Galika runs a regular route back and forth between Planet Hawai'i and Planet California. The Galika is 136,000 dtons of cargo. So even if it visits 1/month, its absorbing 50% of the cargo trade of the entire planet by itself. If you have two on alternate schedules, they'd absorb almost the entire trade volume between them. This would require a massive cargo handling starport that runs on overdrive on the day the liners arrive and a few days after distributing the cargo and on low staffing the rest of the month. Probably have some kind of "Stevedore Reservists" or a lot of robots that can be shut down. The rest of the trade would be smaller vessels.

You could structure it so that you have a LASH system where large cargo ships going to bigger ports exchange non jump cargo pods, either with tugs or self propelled pods. The Galikas running along the main from California to Shanghai would refuel at Hawaii, Guam, the Philippines and quickly exchange pods or lighters while doing so. The rest of the trade would be made up of smaller vessels. This wouldn't require nearly as big a port in the smaller systems, as they wouldn't be *directly* dealing with the Galika.

Generally, freighters in Traveller are about 50% cargo capacity, assuming they are jump 1 or jump 2. Real Hawai'i gets 2-4 smallish container ships (3600 TEU) a day. That plan would be a few 5000 dton freighters, with smaller ships picking up the rest. Fewer of these if the Galika is involved, either LASH or direct load.

However, because of how Traveller ship construction works, there's not really a lot of economies of scale until you get really big. Fuel, engines, bridge, crew, etc scale linearly for most ship sizes.. Even a fat trader is 50% cargo. I wouldn't expect that you'd want 50 fat traders a day buzzing around your port, but you could. Personally, I tend to think that the majority of freighters are about 2000 or 2500 dtons. That should be able to go to most D and C ports as well as the B high ports. And it gives a decent volume of freighters in system. Instead of one or two bigger ships, you have dozen or so ships of various sizes, most of which are "adventurer class" (ie 2500 dtons or less),making them easy to make floor plans for and use on adventures.

Regardless of what decision you make about your trade, it should take into consideration the ports and populations of the planets along your trade route. And your logistics, to whatever extent you want to think about them, should factor in that just placing an order across interstellar distances is a week or more before they even get it. Today's world, where I sent an email this morning placing an order and got shipping confirmation that afternoon is not Traveller reality. You can't even be sure what day a ship is arriving, just when they hope to have it arrive. Because you can't check exactly when it left faster than when it arrived.

All this means that interstellar trade has to be a bit more loosey goosey than modern shipping is. And that's going to make interstellar trade relatively less efficient and profitable than today's maritime trade.

Wouldn't depend on the strength of the container and it's materials?

If you used balsa wood as the flooring, I wouldn't be surprised if anything heavy breaks through.
Yes. And shipping containers are standardized so that everyone can build their cranes, ships, trucks, etc to handle the specs. As I said, you can invent better shipping containers with sci fi materials as your standard. And, assuming you can scale everything else to match, you can have more mass per volume if the materials shipped produce it.

Which is fine, but it makes discussions hard because it eliminates even more of the few facts we have for analysis

If you treat the container as a hull, you can armour plate it.

And reinforce it.

Yes, but the problem is not the part where its on the ship. Its the part where it is in the port . Real world shipping containers get taken off a container ship and then stacked ashore until they can be put on the back of a truck, train, barge, or different container ship. So all those things have to account for the additional weight too.

You could put a GPS tracer on it and let it orbit the planet.

Space isn't like the ocean, though. You can't jump straight from Regina to Rhylanor like you can sail from Rotterdam to Shanghai. And the fuel requirements for jumping are enormous. You are refueling every jump.

Ocean liners also have the ability to go straight to another container port that suits them. Starliners don't get to do that. There is only 2 class B or better destinations within Jump 2 of Regina and one of those has a small population. Whereas LASH can be exchanged as the main ship continues. You have to have the lighters either way.

If you want to have space stations that are as large as a container port, you can do that. The economics are entirely made up. If you want to unload your Galika at the high port (it can't land on the planet), then you need 136,000 dtons of warehousing for that cargo. Or the ability to drive it straight from the Galika to the ships that are going to take it down to the planet or out to Mars and the Jovian moons.

As I said, it all comes down to what you think is reasonable for your space port. If you think the highport is like the Death Star in size with vast amounts of warehousing, docking for its own lighters, and the crew space, sure. That's definitely a way to go. But the number of routes where there's an A/B starport at both ends is less than you would think. And even rarer if the planet is expected to be high population.

If you aren't doing LASH, you are probably running a lot more smaller hulls that each have to have jump drives. And that means they need more engineers, ASTROGATORS, and stewards overall.

However, my point is not that my way is the best way. Its that there are multiple ways that make sense given what little information we have about space trade economics.
No, space is not the ocean, but logistics is logistics. Up through the early 19th century it really hadn't changed other than ships getting larger and slowly getting faster. The concept of containerization revolutionized the break-bulk cargo world (i.e. everythign that wasn't carried in great quantities like oil, coal, grain or ore). Ro-Ro cargos made transporting auto's more efficient in the same way.

So the extra costs associated with keeping a LASH barge maintained - along with the widespread adoption of containers - relegated LASH barges to the dustbin of inefficiency. The same principle applies to one larger ship transporting many smaller ships - at least as far as logistical transportation economics says from past human history. In the Dune universe large transports transport multiple smaller ships instead of going point-to-point. That's by choice and the advantage of near instantaneous travel across unlimited distances. That may not be a good comparison due to the other issues being injected into the argument.

Unloading could be faster by exchanging entire modules of cargo - for the ship. Though that excludes the extra costs for the tugs and lighters and other infrastructure required to make that model work. You can do that with a modern ship today, too, but its far more efficient to dock the ship and use specialized cranes to quickly unload and reload. That also gives your ship time to refuel, restock and for minor maintenance to be performed on engines and such that are temporarliy shut down while in port (another consideration oft overlooked).

A merchant is going to seek out the cheapest overall operation to transport cargo. If the highest cost is the ship operation, then they'll try to optimize that (which could account for a ship jumping in at 100D, maneuvering to 99D and taking of fuel and dropping off modules and then jumping back out - that is the most efficient use of the transport itself - no guarantee its the most efficient system).

Modelling ships is going to be hard in Traveller since no data exists - it is literally all made up. However one can look at cargo transport in reality (historical as well as current) to see what kind of trade occurred in past based on population and wealth levels. Traveller costs make it unlikely to transport basic things like grain or raw ore since all cargo's price (for the merchant) at Cr 1,000/dton, though costs can vary. Traveller also assumes you can have ships built in 10s of thousands of tons. But we have no clue if they can economically operate at that size - perhaps on a few planetary routes they might. From a PC-gaming perspective everrything is at the far-smaller scale - tramp merchants carrying theequivallent of a few dozen semi's or teeny passenger liners (type-M). Those ship-sizes make sense from a gaming perspective, but not from an economic model that deals with trillions of beings and thousands of habitable planets spread across hundreds of light-years.

I don't think any one way is truly the "best" way. Look at how railroads work. You have a (possible) fad called Precision Scheduled Railroading - which has fewer but longer trains. This benefits railroads, but doesn't benefit anyone else. US trains can be 10,000ft long whereas a Japanese or European train may only be 50-70 cars long. They optimize speed over cost savings. Malcolm McClean (SeaLand) came into shipping via trucking, and pushed early container ships which now rule the waves for general cargo. He also pushed for faster cargo ships instead of slower ones (an idea from the old clippers that used to travel to CA from the east coast). Shaved days off transatlantic crossings - but ships traveling at 31 kts burned a lot more fuel than those travelling at 15-17 kts. All those fast freighters ended up being retired and sold to USN as fast replenishment ships because shippers were not willing to pay for that (airfreight has taken over for part of that, but the bulk is still shipped via slowboats).

There is a series of books that provides a LOT of historical context and explanation called Conway's History of the Ship. The one for this discussion is called The Shipping Revolution: The Modern Merchant Ship. There is a 2nd book leading up to this one called The Golden Age of Shipping - The Classic Merchant ship that rounds out this picture. The entire series is just plain good - and the military books are also very relevant to Traveller. Highly recommended.

There isn't any one best way has been my point all along. It's going to depend on what made up factors you think are important. I think the lack of high quality ports in a lot of systems, the communications deficit, the way jump fuel scales, and some other factors like what's fun for my game means that using LASH on large ships running along a main between ports that can actually support them directly makes the most sense to me. I don't expect that to be the same resolution for other groups.

There are lots of solutions. Not just one possible solution.

Somewhere in Charted Space there are efficiency consultants complaining that maneuver drives are waste of space when a ship is in jump space and jump drives are a waste in space when moving in normal space or planet side. I can see these consultants trying to convince merchant lines that maneuver and jump drives should be on different ships and the maneuver drive ship serving multiple jump drive only ships.

@Vormaerin I'll clarify, because I can't find the source of the information - what are LASH ships? Something like Tucker Venturer Class Fast Freightliner?
Some ship with a large jump drive, capable of carrying smaller ships?

The LASH concept is used in GT Far Trader.
Lighter Aboard Ship (LASH)
Lighters are non-starships, usually hull class 100 or larger, used to off-load
unstreamlined freighters on planets without an orbital port. Specialized starships are
designed to carry these lighters directly, much like battleriders and their tender
10,000-ton Lighter-Aboard-Ship (LASH)
Tender (TL10)
This vessel is nothing more than a carrier for fifteen 800-
ton lighters. With lighters attached to the external cradles, the
ship is effectively 22,000 dtons; the jump drives are sized
accordingly.
A LASH tender is more expensive than an equivalent
conventional freighter, especially when the cost of the
lighters is taken into account, and cannot be overloaded (due
to strength limitations on the external cradles). It is superior
in two respects, however. First, it has the minimum possible
replace all lighters in less time than it takes them to refuel.
Second, it is exceptionally flexible, as each lighter is capable
of landing at a separate destination.

@Vormaerin I'll clarify, because I can't find the source of the information - what are LASH ships? Something like Tucker Venturer Class Fast Freightliner?
Some ship with a large jump drive, capable of carrying smaller ships?
In the real world, LASH is "Lighter Aboard SHip". It is basically a tug carrying barges to destinations they can't reach. It has some niche applications, but mostly is more expensive than alternatives. With maritime shipping there are trains to take cargo to secondary destinations and it is possible for merchant shippers to just decide to make larger ships that major ports will just adapt to. In the real world, freighters get larger primarily by getting wider, so they can still use the same berths if the harbor is otherwise large enough. And harbors like Felixstowe and Rotterdam will dredge and otherwise modify to make sure that happens.

As Sigtrygg pointed out, there's an example of such a ship in GURPS Far Trader. But, basically, its a jump carrier for freighters instead of warships. The reason that I think it works in Traveller is that space travel is quite different than oceanic travel. Economies of scale are much reduced because most ship components are % of hull, so big freighters don't carry that much more stuff as a percentage of their ship. Fuel usage, engine size, most crew functions, etc scale linearly. And, most importantly, the jump drive/jump fuel is the largest component of a starship. So you don't lose as much cargo space using LASH in Traveller as real world barge transports do.

But the real difference is ports. In maritime trade, you absolutely sail to the big port that can handle your ship and then let trains, trucks, barges, and small feeder ships move the freight to all the secondary destinations. The traveller universe doesn't have that option. Very large freighters require large high ports to handle them. At the very least, B or A. And arguably not all of those can handle super large ships. And if you do a spoke and hub system, you have to put all your cargo onto other jump capable ships to reach secondary star systems. There's no trains or barges to take cargo you drop off at the A port to all the C and D ports. Jump drives, jump fuel, and astrogators are required for every one of those ships.

If you have a situation where you can directly jump from one high pop planet with a good port to another such planet, a megafreighter is the most efficient. If your large freighter has to make a string of jumps to reach its real destination, it basically can't trade at all the intermediate locations because there's no highport or its too small.

One solution is the unlisted corp owned starbase like you mentioned elsewhere. Another solution is LASh, so that the large freighter can exchange cargo quickly without needing to actually have a high port that can handle it. There's no way to know "for real", but I feel like maintaining interplanetary ships (lighters) along a trade route is more feasible (and less distorting of the Traveller map) than massive private starports.

One other major advantage of the LASH model - you can jump much more often.
20 mins to unload the lighters, 20 mins to dock new lighters and transfer crew and fuel.
A jump schedule of 8 days rather than 14...

Assault carrier being a variant.

As regards to refuelling, that might take a tad longer.

One other major advantage of the LASH model - you can jump much more often.
20 mins to unload the lighters, 20 mins to dock new lighters and transfer crew and fuel.
A jump schedule of 8 days rather than 14...
Yeah.

Real world logistics focus on two things: travel time and port slots. Port slots, whether airports or seaports, are usually the biggest bottleneck. That is why you see a constant expansion in the size of cargo craft and almost all of it is width, so it doesn't take up more slots than a smaller ship. The other advantage is that cost of upgrading the ports primarily falls on taxpayers. And, while port fees might increase, that just drives away the smaller guys from competing for your slots.

Traveller doesn't have railways, though. So you can't ship everything from China headed for Europe to just a handful of ports and send it on by truck and rail. Anything you are trading that is not destined for that solar system needs to go onto ship with a jump drive. And that ship needs a slot. Even if you build small slots and big slots, the small slots are taking up space that could be a big slot. Rotterdam port data suggests that only about 30% of the cargo delivered to Rotterdam gets put on a feeder ship to another port. I feel that would be much higher in Traveller if the big cargo ships only traded at the A/B ports and fanned everything else out.

The other thing about Traveller is that it does not have an abundance of good high ports. There are solid game play reasons for that, but what the 'in universe' reason would be isn't clear. Either there is not much trade, which seems like a bad idea, or there is some unknown factor that makes big commercial ports in space harder/more expensive than we might think, so merchants can't pressure all these planets into having class B starports.

Speed is the other issue. In the real world, the more cargo you can fit per slot, the better. And travel speed is a balance between fuel costs (which favor going slow) and volume of cargo shipped (which favors going fast). It doesn't really work like that in Traveller. A jump 4 ship is going to carry about half as much cargo as a Jump 2 ship (most jump 2 cargo ships are about 50% cargo. A jump 4 ship would eat up another 25% of the hull space in extra fuel, engines, and crewing)). So you aren't really going to deliver more cargo by going faster and you aren't going to save money on fuel. (There are *some* costs that are time dependent, but fuel dwarfs them). The only way to speed up cargo delivery is to reduce time in system so your jump ship gets farther.

I feel most trade would be on large adventure class ships or slightly larger (2000-5000 tons) because the widest range of ports can support those. But for trade routes linking two major worlds along a main, I feel like a LASh system would address a lot of these oddities of Traveller logistics.

1) The mother ship only needs a "slot" at the origin and destination
2) Your corporation only needs a small station or section of the starport in the C/D starport systems for its lighters and crew R&R, not something massive and capable of handling the megafreighter itself.
3) LASh allows the megafreighter to trade at the intermediate stops which it otherwise couldn't do due to lack of facilities
4) It speeds up transit times to 1-2 days in system, allowing 3 jumps/month instead of the typical 2.
5) It allows the configuration of the ship to a variety of specs: you can have cargo liners, fuel liners, passenger liners, etc.

Again, there are certainly other solutions depending on what assumptions you make about the fiction behind Traveller's oddities. This is the one that works best for me, based on my understanding of logistics systems in the real world and how Traveller systems are. And the fact that I want a lot of trade in the Imperium vs a frontier ships are rare feel.

In the real world, LASH is "Lighter Aboard SHip". It is basically a tug carrying barges to destinations they can't reach. It has some niche applications, but mostly is more expensive than alternatives. With maritime shipping there are trains to take cargo to secondary destinations and it is possible for merchant shippers to just decide to make larger ships that major ports will just adapt to. In the real world, freighters get larger primarily by getting wider, so they can still use the same berths if the harbor is otherwise large enough. And harbors like Felixstowe and Rotterdam will dredge and otherwise modify to make sure that happens.

As Sigtrygg pointed out, there's an example of such a ship in GURPS Far Trader. But, basically, its a jump carrier for freighters instead of warships. The reason that I think it works in Traveller is that space travel is quite different than oceanic travel. Economies of scale are much reduced because most ship components are % of hull, so big freighters don't carry that much more stuff as a percentage of their ship. Fuel usage, engine size, most crew functions, etc scale linearly. And, most importantly, the jump drive/jump fuel is the largest component of a starship. So you don't lose as much cargo space using LASH in Traveller as real world barge transports do.

But the real difference is ports. In maritime trade, you absolutely sail to the big port that can handle your ship and then let trains, trucks, barges, and small feeder ships move the freight to all the secondary destinations. The traveller universe doesn't have that option. Very large freighters require large high ports to handle them. At the very least, B or A. And arguably not all of those can handle super large ships. And if you do a spoke and hub system, you have to put all your cargo onto other jump capable ships to reach secondary star systems. There's no trains or barges to take cargo you drop off at the A port to all the C and D ports. Jump drives, jump fuel, and astrogators are required for every one of those ships.

If you have a situation where you can directly jump from one high pop planet with a good port to another such planet, a megafreighter is the most efficient. If your large freighter has to make a string of jumps to reach its real destination, it basically can't trade at all the intermediate locations because there's no highport or its too small.

One solution is the unlisted corp owned starbase like you mentioned elsewhere. Another solution is LASh, so that the large freighter can exchange cargo quickly without needing to actually have a high port that can handle it. There's no way to know "for real", but I feel like maintaining interplanetary ships (lighters) along a trade route is more feasible (and less distorting of the Traveller map) than massive private starports.
LASH failed because other methods offered more variety and overall cheaper operations. Water-borne trade is the cheapest method of transporting goods in bulk - but you are limited by where you can go. It was a good idea that didn't pan out.

In general I think you are right about the scalar model of costs for ships in Traveller - though you CAN gain economics of scale with larger ships as far as crew requirements go. Things like Pilots, navigators and such remain the same regardless of ship size. And crew requirements have been changed somewhat for civilian ships, depending on the version being discussed. Today a 30-40 man crew can operate a 10,000 ton tanker or a 300,000 tanker. Traveller never really got those needs right.

For maritime trade ports aren't a limitation, but just another part of the equation. Many smaller ships that carry bulk cargo maintain their own on-board cranes or unloading devices. Just like today super-large freighters will only be on the biggest routes - mid-sized routes will get the mid-sized freighters and the smaller markets will get the small freighters / free traders. The exception might be smaller worlds might have busier ports due to location as transloading ports instead of point-to-point. I can see it working both ways (in theory the Traveller map shows the same, but the actual worlds/trade volumes rarely support that logic). The hub-and-spoke method is tried and true for both cargo and passengers. I think we are in agreement on this point.

You are going to see cargo lighters / space-to-planet shuttles at pretty much every starport - especially those that have orbital components. A busy port is going to have more than one orbital station collectively known as the "high port" simply because there wouldn't be near enough docking stations. There would be only so much hull real estate for ships to dock at. Which actually brings up another question - why so many Traveller ships are ill-designed to dock nose-in to stations to efficiently unload and reload cargo. Similar to cargo quays, but ships docking nose first greatly increases the possible number of ships that could be simultaneously dock. And stations are going to not have docking locations spread around because cargo will be stored on only so many levels, so ships will dock at those levels. Like a port there's internal infrastructure required to move that cargo around and store it (as well as keep it moving for shuttles and lighters to take down to the world).

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