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Spun off from another thread:

Not Online!!! wrote:

 Haighus wrote:

Imperial logistics are a separate albeit related topic IMO. The true unreliability of warp travel in particular is highly debatable given the Imperium relies on regular and massive interstellar travel for its worlds to function on a regional and galactic scale. My personal thoughts are that warp travel is usually safe and predictable to fairly tight margins of error, but gets dramatically more dangerous if there are local inclement warp conditions (squalls and storms) or around major warzones (from the impact of death and violence on the warp). Clearly most ships reach their destinations in reasonable timeframes, and repeatedly do so for hundreds or even thousands of years in many cases (based on age of vessels).

Logistics are not separate and even if warptravel is in calm areas predictable, f.e. this little snippet from the lexicanum:https://wh40k.lexicanum.com/wiki/Warp_jump

Estimating the length of a Warp Jump, at least for the Imperium, is extremely difficult and inconsistent. As the Warp is ever-shifting, determining the length of a jump is difficult for even even semi-fluctuating passages. The Questio Logisticus branch of the Administratum is dedicated to this difficult task.[11]

One example is given for travel between the Hive World of Proxx and the Mining World of Hephastian. These planets are separated between dozens of light years and a standard voyage in the warp will take one to six weeks. However some voyages have been recorded as taking 1,200 years and another in as little as two minutes. 32% of the voyages have yet to reach their destination.

And that is not even going into communication.

So a 32% failure rate, if generally applicable, would be bonkers and incompatible with many Imperial vessels being hundreds, thousands, or even tens of thousands of years old.

Will look into the primary source (cited as 8th edition rulebook) when I get chance, Lexicanum sometimes misses the nuance or context.

IIRC there are stable routes, beacons & Warp Gates that all allow for reliable travel. They also use non-warp ships for less important cargo.

Beast is correct. There are several factors that go into warp travel:

* The stability of the warp route. Some routes are relatively safe and stable. Others are more of a mess.

* The skill of the navigator. The better they are, the less likely you are to hit a hazard.

* The duration of the voyage. While the length of the voyage doesn't properly correspond to the distance from point A to point B in the materium, generally the more time you spend in the warp, the more opportunities you have to slip up and hit a timestorm or whatever.

* The quality of your equipment. If your gellar fieldscan't take much stress or your engines can't maneuver quickly, you're more likely to run into a problem.

Think of it like driving in icy weather. Some roads will be treated with road salt while others won't. Some roads will be on hills or have twists that are tricky to navigate. Sometimes a road will be closed, and you'll have to take a detour. If your driver is good at driving, they'll be more likely to avoid slipping on the ice or taking a turn too fast or plotting an inefficient route in the first place. If your tires are low on air or you have regular engine trouble, you're in more danger. If you're driving 100 miles, you'll have more chances to mess up than if you're driving 1 mile.

And even if you have a good driver, a good car, favorable weather conditions, and a short drive, there's still always a small chance that you'll have an accident.

It used to be great and thematic and underpin a lot of the setting. Then they realised that meant the same handful of people couldn't be everywhere so its become as bad as travel in game of thrones.

The_Real_Chris wrote:
It used to be great and thematic and underpin a lot of the setting. Then they realised that meant the same handful of people couldn't be everywhere so its become as bad as travel in game of thrones.

How do you mean? I've read a lot of old BL stories and a lot of more recent ones. Warp travel seems to be consistently handled as risky but not actually likely to result in your doom. In more recent stuff, sailing directly through the cicatrix maledictum is presented as extremely risky, but only in the same sense that trying to sail around the Eye or the Maelstrom or an active warp storm.

Has any of that changed?

Warp travel has to be reasonably reliable and safe for the simple reason that the Imperium has hive worlds that are utterly dependent on imports to survive, yet they have survived for thousands and thousands of years being serviced by ships hundreds or thousands of years old.

Warp travel is reliable... as long as you stick to well charted warp routes and/or gates, make small jumps and have a decent navigator.

Mess around with those variables and the reliability starts falling apart.

Warp travel is a clear analog to the age of sail. There were known trade routes that had seasonal storms, navigational hazards but that could be traversed with reasonable predictability. Passage across the North Atlantic, for example, was pretty well mapped out, as was coastal traffic around Europe.

However, navigating the Cape of Good Hope was never easy, and going to the Pacific via the South Atlantic was always difficult.

40k replicates this. There is a regular trade within the Imperium, and patrols and fleets at known nav points keeps it safe and reliable. Going outside these routes increases risk and of course a gale or hurricane could wreak havoc.

The main thing to keep in mind is that failure =/= the ship is destroyed or lost forever. A failed warp jump most likely means the ship is just off course from its target destination, or just late, or early, or hit some turbulence and took some damage but got out alive, etc...

Warp travel is never safe, its never 100% reliable, but it is functional and enables FTL trade and transportation with only minor hassle.

Commissar von Toussaint wrote:
Warp travel is a clear analog to the age of sail. There were known trade routes that had seasonal storms, navigational hazards but that could be traversed with reasonable predictability. Passage across the North Atlantic, for example, was pretty well mapped out, as was coastal traffic around Europe.

However, navigating the Cape of Good Hope was never easy, and going to the Pacific via the South Atlantic was always difficult.

40k replicates this. There is a regular trade within the Imperium, and patrols and fleets at known nav points keeps it safe and reliable. Going outside these routes increases risk and of course a gale or hurricane could wreak havoc.

I think this is very much the intention. I have seen numbers in the ballpark of about 5% of vessels being shipwrecked on merchant routes during the Age of Sail. This seems reasonable to me- most of those ships would have done multiple journeys before their demise so the number of successful journeys would be much higher than 95%.

Now compare that to the numbers below...

I found the primary source- it is in the 8th edition rulebook appendices at the back of the book. Here is the text:



Some things stand out to me. Firstly, this is a rare example of a modern in-universe perspective, and therefore much more fallible than the "omniscient narrator" approach typically used by modern GW. Secondly, Lexicanum misquotes the failure rate as 32%, when in the lore it is 22%- notably less, albeit still enormously high. Edit: I have now corrected the Lexicanum entry to 22% to avoid further confusion.

The route in question has ~3 convoys a year, for a total of ~6000 convoys over the approx. 2000 years recorded. 22% of these never reached their destination, despite that meaning that an average vessel carries out a mere 5 trips before disappearing. Some vessels will be still in transit rather than lost, but the number remains staggeringly high. The distance is "a few dozen light years", apparently a "fairly short" journey, with longer routes being more dangerous and presumably having higher loss rates. This is in contrast to other lore suggesting the majority of Imperial warp travel occurs at distances less than 5 light years and not requiring navigators on board. The route time is "typically" between 1-6 weeks, with a recorded range of 2 minutes to 1200 years- nothing surprising there. Allegedly, this route has the most stable classification.

A 22% journey loss rate on stable, routine, short routes is essentially incompatible with established lore on centuries or millennia old vessels and major characters flitting around the galaxy for decades or centuries. An empire could be sustainable at those loss rates, but the ship production required to sustain this would be colossal. Sector warfleets are typically 50-75 vessels. At those loss rates, 10-15 new warships would need to be built for every 5 journeys the fleet makes. Patrols would be impossibly dangerous, not a routine part of Navy life with valuable capital ships deployed to them. So clearly the warp route figures above are not generalisable.

So what could explain this? I have a few possibilities, a combination of which are plausible:

1) The Navy adjutant is wrong- either simply mistaken or politically motivated. For example, the actual loss rate may be 2.2%- a simple misplaced decimal point. This mistake could have been made by the adjutant or some unnamed administratum clerk. 2.2% would still be a high failure rate, but then a typical ship would perform 50 journeys rather than 5- much more in keeping with other lore. The description of this being a short route may also be wrong.

However, the conclusion of trusting in faith rather than science would suggest a political motivation for this piece, as we know that science and technology can influence warp travel. Warp journeys may be variable and risky, but if they have typical travel times there will be a distribution and risk tables etc. There is technology and quality of navigators to consider, with Grey Knights vessels known to be the fastest and most reliable, and the merchant marine probably typically the least reliable (on the whole- some will be able to afford the best equipment). A Navy adjutant won't know about the Grey Knights, but will know there are differences in quality between warp drives and gellar fields and navigator skill, and these do influence travel time and safety within the Immaterium on the whole. So I think this adjutant may have an agenda.

2) The route is misclassified- not uncommon within the Imperium. Rather than being the most stable kind of warp route, the route may actually be significantly more volatile. It could also have changed over 2000 years without the classification being updated.

3) Losses amongst merchant vessels (this being a trade route) may be significantly higher than amongst military vessels, due to aformentioned reasons of quality of equipment and navigators. It may even be possible that this route is generally done via calculated jumps without a navigator, despite being much greater than the typical 5 light year "safe" limit for this. That could explain the high loss rates.

4) The distrubition amongst ships is not even- many ships are lost on their first voyage, a few lucky ships ply the void for centuries or millennia. I don't think this is supported by the lore though.

In summary, I do not think this is a representative example for wider Imperial warp travel, except maybe during the formation of the Great Rift, or within Imperium Nihilus. Those are a short period of time within Imperial history though, rather than the 2000 years shown above.

You’re also dependant on the skill of your Navigator, engine room crew and the quality of your ship overall.

If your crew are well practiced, your engines and gellar field properly maintained and sanctified? You’re less likely to have a problem than if you’re piloting a rickety pile of rust no self respecting Tech Priest would go near.

Assessing what went wrong on a given journey of course kind of requires finding the ship - which won’t necessarily be wreckage. But if it’s just Gone? Perhaps translocated somewhere in the Ghoul Stars, you’re just not gonna know what actually caused it to be Gone.

I see that as the biggest issue with Warp Travel, as it limits study and understanding of accidents and disasters. So if there’s perhaps an inherent design flaw, you may never find out about it.

 Haighus wrote:

Some things stand out to me. Firstly, this is a rare example of a modern in-universe perspective, and therefore much more fallible than the "omniscient narrator" approach typically used by modern GW. Secondly, Lexicanum misquotes the failure rate as 32%, when in the lore it is 22%- notably less, albeit still enormously high. Edit: I have now corrected the Lexicanum entry to 22% to avoid further confusion.

thanks for that. I also checked the german book, it's 22 there aswell, altough the citation still requires the propper page number.

Spoiler:

The route in question has ~3 convoys a year, for a total of ~6000 convoys over the approx. 2000 years recorded. 22% of these never reached their destination, despite that meaning that an average vessel carries out a mere 5 trips before disappearing. Some vessels will be still in transit rather than lost, but the number remains staggeringly high. The distance is "a few dozen light years", apparently a "fairly short" journey, with longer routes being more dangerous and presumably having higher loss rates. This is in contrast to other lore suggesting the majority of Imperial warp travel occurs at distances less than 5 light years and not requiring navigators on board. The route time is "typically" between 1-6 weeks, with a recorded range of 2 minutes to 1200 years- nothing surprising there. Allegedly, this route has the most stable classification.

A 22% journey loss rate on stable, routine, short routes is essentially incompatible with established lore on centuries or millennia old vessels and major characters flitting around the galaxy for decades or centuries. An empire could be sustainable at those loss rates, but the ship production required to sustain this would be colossal. Sector warfleets are typically 50-75 vessels. At those loss rates, 10-15 new warships would need to be built for every 5 journeys the fleet makes. Patrols would be impossibly dangerous, not a routine part of Navy life with valuable capital ships deployed to them. So clearly the warp route figures above are not generalisable.

So what could explain this? I have a few possibilities, a combination of which are plausible:

1) The Navy adjutant is wrong- either simply mistaken or politically motivated. For example, the actual loss rate may be 2.2%- a simple misplaced decimal point. This mistake could have been made by the adjutant or some unnamed administratum clerk. 2.2% would still be a high failure rate, but then a typical ship would perform 50 journeys rather than 5- much more in keeping with other lore. The description of this being a short route may also be wrong.

However, the conclusion of trusting in faith rather than science would suggest a political motivation for this piece, as we know that science and technology can influence warp travel. Warp journeys may be variable and risky, but if they have typical travel times there will be a distribution and risk tables etc. There is technology and quality of navigators to consider, with Grey Knights vessels known to be the fastest and most reliable, and the merchant marine probably typically the least reliable (on the whole- some will be able to afford the best equipment). A Navy adjutant won't know about the Grey Knights, but will know there are differences in quality between warp drives and gellar fields and navigator skill, and these do influence travel time and safety within the Immaterium on the whole. So I think this adjutant may have an agenda.

2) The route is misclassified- not uncommon within the Imperium. Rather than being the most stable kind of warp route, the route may actually be significantly more volatile. It could also have changed over 2000 years without the classification being updated.

3) Losses amongst merchant vessels (this being a trade route) may be significantly higher than amongst military vessels, due to aformentioned reasons of quality of equipment and navigators. It may even be possible that this route is generally done via calculated jumps without a navigator, despite being much greater than the typical 5 light year "safe" limit for this. That could explain the high loss rates.

4) The distrubition amongst ships is not even- many ships are lost on their first voyage, a few lucky ships ply the void for centuries or millennia. I don't think this is supported by the lore though.

In summary, I do not think this is a representative example for wider Imperial warp travel, except maybe during the formation of the Great Rift, or within Imperium Nihilus. Those are a short period of time within Imperial history though, rather than the 2000 years shown above.

1. Possible, but at 2.2 % would we really classify this as dangerous? And yet we hear constantly that warptravel is supposedly dangerous.

2. Administratum being what it is possible, however seeing as one of the planets on the route IS a hive and possible more relevant due to production output and requirements for maintenance that would be doubtfull. Further, Nephilim was known for not being particulary unstable, to the contrary since it's the pariah nexus sector.

3. Piracy may very well be a larger issue. Seeing as sector fleets are somewhat smallish.50 - 75 vessels for an cube of about 200 lightyears per side meaning a volume of about 8'000'000 cubiclightyears. fwiw, around the earth we have about 4 stars in 1000 cubiclightyears. Meaning the sector fleet has to patrol a potential of about 8'000 possible star systems, though that will not be where the majority of traffic happens, contrary, the traffic will be focussed on the populated "worlds" . Assuming normal milkyway values we got about 300'000'000 inhabitable earthlike potential planets spread on between 100 billion to 400 billion starsystems. going with the middle value that'd mean we got about 250 billion starsystems containing 300'000'000 inhabitable worlds. However that' would give us a average of 0.0012 of potential inhabitable systems which would mean a sector fleet would have to patrol about 9.6 systems / sector which seems actually rather managable at a first glance.
However we would need to add systems to this due to mining world locations an average we don't really have potentially nubers on, which would spread the sector fleet even further. Which probably would not house fleets due to a lack of dockyards, so pirates may well pray on mining and factory vessels which in turn would increase the loss rate drastically i reckon and getting merely attributed to the warp.


4. Ship availability and age of production may very well play a role. Assuming the best of the best goes to the navy, marines and mechanicum and rogue trader dynasties, chances are that freighters, cargo and mining / factory vessels are secondrate. DAOT ships will be innevitably better built, so will great crusade era ships be better compared to newer shipt types due to technology loss.

I would class 2.2% loss rate as dangerous! For reference, assuming an average 6 week journey time, that would be a ship loss roughly every 50,000 hours of time spent in the warp (from the perspective of those in realspace). That is a loss rate similar to the V22 Osprey (including its testing phase), a vehicle recognised as being dangerous. It is more dangerous than the Age of Sail, when crossing the oceans was viewed as a perilous endeavour.

22% is worse odds than Russian roulette, for each voyage.

I don't think piracy is a factor in these numbers- the suggestion is that these are ships lost in the warp, not losses on the journey altogether. Generally, if a ship makes it to the destination system, the other world will know they arrived in system even if they are then lost to piracy on approach. I am not aware of significant piracy of vessels during warp transit.

 Haighus wrote:
I would class 2.2% loss rate as dangerous! For reference, assuming an average 6 week journey time, that would be a ship loss roughly every 50,000 hours of time spent in the warp (from the perspective of those in realspace). That is a loss rate similar to the V22 Osprey (including its testing phase), a vehicle recognised as being dangerous. It is more dangerous than the Age of Sail, when crossing the oceans was viewed as a perilous endeavour.

22% is worse odds than Russian roulette, for each voyage.

I don't think piracy is a factor in these numbers- the suggestion is that these are ships lost in the warp, not losses on the journey altogether. Generally, if a ship makes it to the destination system, the other world will know they arrived in system even if they are then lost to piracy on approach. I am not aware of significant piracy of vessels during warp transit.

Again, though, the exemple given is in the nephilim sector which is a calm region thanks to necron shenaniganry.
It may well be possible that calculated jumps have a far higher accuracy than Navigator reliant longjumps. Which in turn would make star systems between worlds even if uninhabited important and probably where the pirates raid.

And piracy was noted a big problem to the point the lexicanum has a separate entry on it.

I think any time you deal with specific numbers in GW lore, you're asking for trouble. If nothing else, GW's "everything is canon" approach is going to mean that if you can quote one source, other authors are simply going to ignore that point if it's not convenient.

The warp travel section from one of the RPGs is more likely to have a compromise between "We need to be able to use warp travel to get somewhere" and "Warp travel needs to be somewhat risky" for practical reasons.

 Haighus wrote:
I would class 2.2% loss rate as dangerous! For reference, assuming an average 6 week journey time, that would be a ship loss roughly every 50,000 hours of time spent in the warp (from the perspective of those in realspace). That is a loss rate similar to the V22 Osprey (including its testing phase), a vehicle recognised as being dangerous. It is more dangerous than the Age of Sail, when crossing the oceans was viewed as a perilous endeavour.

22% is worse odds than Russian roulette, for each voyage.

I don't think piracy is a factor in these numbers- the suggestion is that these are ships lost in the warp, not losses on the journey altogether. Generally, if a ship makes it to the destination system, the other world will know they arrived in system even if they are then lost to piracy on approach. I am not aware of significant piracy of vessels during warp transit.

This seems to me a classic example of Sci-Fi Writers Can't Do Math, which I believe is a well-established trope.

I'm too lazy to look it up, but 22% seems like Battle of the Atlantic level losses during its worst phase.

I'm with the Doc on the other factors being important. Good ships, good navigator, known route, etc. The vast majority of the canon treats warp travel as reliable but not perfectly safe. There is always some risk, but it beats the alternative of not going.

I've always kind of viewed it as failure rates of warp travel are actually very low, but its just that the vast scale of the Imperium means it is still a day to day thing that just happens. I know the meme is your average warp journey ending in daemons erupting everywhere and 90% of the crew dieing, but if that were truly the case the Imperium would have collapsed in on itself ages ago.

As Commissar said above, its down to the writers just not understanding math and scale. There are innumerable ships entering the warp on a daily basis considering the Imperium has a million+ planets - yes some feudal world might get 1-2 ships showing up per year, but that is balanced out by hive worlds getting probably hundreds of ships of food per day, and terra alone is likely in the thousands, shipping pilgrims, food, water, etc. Even a failure rate of 0.1% means that for every 1 million ships entering the warp, 1,000 will have some sort of shenanigans going on, and lets face it, the Imperium probably has more than 1 million warp capable ships between navy vessels, merchant ships, rogue traders, and so on.

To me what is more confusing is the status of warp travel in the Dark Imperium.

I originally thought it was like long night all over again. But then you read the Vigilus stuff and it sounds like the Astronomican can cut through this corridor enabling navigation into and around at least part of the Dark Imperium.

Of course, the Tau do just fine without navigators, just keep doing the short jumps and you can get to where you are going. So my guess is that you still have interstellar travel on that side of the galaxy but it's either very slow or very unreliable.

Commissar von Toussaint wrote:
I'm too lazy to look it up, but 22% seems like Battle of the Atlantic level losses during its worst phase.

Actually, during worst phases of the BotA (both Happy Times) the losses were around ~4%. That's with massive fleet trying to sink shipping and the losses were considered (at the time) unsustainable. Which is why not only 22% is downright stupid, especially considering big warp capable space ship has to be vastly bigger investment than WW2 era steel box with primitive steam engine, even proportionally, but even talking about "just" 2.2% above is silly, that's loss of 1/40 ships every trip, equal to manpower loss ratio in some of the most bloody campaigns in history...

 kurhanik wrote:
As Commissar said above, its down to the writers just not understanding math and scale. There are innumerable ships entering the warp on a daily basis considering the Imperium has a million+ planets - yes some feudal world might get 1-2 ships showing up per year, but that is balanced out by hive worlds getting probably hundreds of ships of food per day, and terra alone is likely in the thousands, shipping pilgrims, food, water, etc. Even a failure rate of 0.1% means that for every 1 million ships entering the warp, 1,000 will have some sort of shenanigans going on, and lets face it, the Imperium probably has more than 1 million warp capable ships between navy vessels, merchant ships, rogue traders, and so on.

Funnily enough, loss of million ships is just Tuesday for the Imperium. Even though supposedly art of constructing new ones is lost and they are irreplaceable or something (if grimdumb sources were to be believed). Go figure

"The Cacodominus was the name given to an extremely powerful alien-cyborg Psyker who was behind The Howling in M34. The Cacodomius' powers were such that it was able to exert complete control over an area of 1,300 planetary systems. Eventually, it was slain by the Black Templars, but the resulting backlash distorted the signal of the Astronomican and burnt out billions of Astropaths across the Imperium. The resulting anarchy from the events resulted in millions of ships being lost and entire Sub-Sectors descending into barbarism."

 Irbis wrote:

Commissar von Toussaint wrote:
I'm too lazy to look it up, but 22% seems like Battle of the Atlantic level losses during its worst phase.

Actually, during worst phases of the BotA (both Happy Times) the losses were around ~4%. That's with massive fleet trying to sink shipping and the losses were considered (at the time) unsustainable. Which is why not only 22% is downright stupid, especially considering big warp capable space ship has to be vastly bigger investment than WW2 era steel box with primitive steam engine, even proportionally, but even talking about "just" 2.2% above is silly, that's loss of 1/40 ships every trip, equal to manpower loss ratio in some of the most bloody campaigns in history...

Yeah 2.2% is still super high, but at least vaguely plausible in a way 22% is not.

 kurhanik wrote:
As Commissar said above, its down to the writers just not understanding math and scale. There are innumerable ships entering the warp on a daily basis considering the Imperium has a million+ planets - yes some feudal world might get 1-2 ships showing up per year, but that is balanced out by hive worlds getting probably hundreds of ships of food per day, and terra alone is likely in the thousands, shipping pilgrims, food, water, etc. Even a failure rate of 0.1% means that for every 1 million ships entering the warp, 1,000 will have some sort of shenanigans going on, and lets face it, the Imperium probably has more than 1 million warp capable ships between navy vessels, merchant ships, rogue traders, and so on.

Funnily enough, loss of million ships is just Tuesday for the Imperium. Even though supposedly art of constructing new ones is lost and they are irreplaceable or something (if grimdumb sources were to be believed). Go figure

"The Cacodominus was the name given to an extremely powerful alien-cyborg Psyker who was behind The Howling in M34. The Cacodomius' powers were such that it was able to exert complete control over an area of 1,300 planetary systems. Eventually, it was slain by the Black Templars, but the resulting backlash distorted the signal of the Astronomican and burnt out billions of Astropaths across the Imperium. The resulting anarchy from the events resulted in millions of ships being lost and entire Sub-Sectors descending into barbarism."

I don't think that is "just a Tuesday"- it is one of the few events important enough to note from the 34th millennium. I think that was treated as a major event that was felt for some time afterwards, on a par with events like the Beheading (at the time that lore was first written).

If that was a common occurrence, "the Howling" wouldn't be remembered as an important event.

 Irbis wrote:

Actually, during worst phases of the BotA (both Happy Times) the losses were around ~4%. That's with massive fleet trying to sink shipping and the losses were considered (at the time) unsustainable. Which is why not only 22% is downright stupid, especially considering big warp capable space ship has to be vastly bigger investment than WW2 era steel box with primitive steam engine, even proportionally, but even talking about "just" 2.2% above is silly, that's loss of 1/40 ships every trip, equal to manpower loss ratio in some of the most bloody campaigns in history...

I stand corrected. I was thinking of the PQ convoys which got wrecked from time to time.

Yes, it is possible to have what are proportionately "negligible" losses and those losses still being a Very Large Number.

And the world being Grim and also Dark with only War, the stories of what goes wrong will be suitable gruesome. Amid all the tales of ship losses, I doubt there's a single instance of "the officer on watch was drunk, fell asleep and disabled the collision alarm because it kept waking him up," which is very much a thing today.

No, you're going to get Nurgle infestations, possessions, crews driven to unspeakable evils, etc. There are no "we missed the channel and ran aground until we were towed off" mistakes in 40k.

 solkan wrote:
I think any time you deal with specific numbers in GW lore, you're asking for trouble. If nothing else, GW's "everything is canon" approach is going to mean that if you can quote one source, other authors are simply going to ignore that point if it's not convenient.

The warp travel section from one of the RPGs is more likely to have a compromise between "We need to be able to use warp travel to get somewhere" and "Warp travel needs to be somewhat risky" for practical reasons.

Which makes the sector size and sectorfleets corresponding to a reasonable ammount with napkin math a bit wierd no?

Personally, I prefer to interpret that passage in a way that 22% of expeditions arrive SUBSTANTIALLY LATE, rather than being lost en-route.

Notice the wording: "22% of expeditions have, as of yet, not arrived to their destination".

So there you have it - an easy way to reconcile that passage with practicality.

As the time scale in the imperium is massive, wouldn't sub-light/near lightspeed freighters make sense? Estimating traveling distances at 10 ly, a delivery time for industrial goods (vehicles, tools, barrels of promethium) of 20 years wouldn't impact an imperium planning in centuries or even millennia. And if multiple freighters are send each year, it's a steady supply of goods. Patroling these freight lanes would make sense, as piracy on sub-light freighters is far easier. The crew will be minimal, bored to tears or even in cryostasis...

Lots of story hooks

I believe they are definitely a thing. Planets which are physically close enough to each other for sublight speed to be practical will do exactly that.

The thing is that most planets are not going to be that close. But Warp drives aren't exactly difficult to craft, and if you are making short jumps you don't really even need a navigator. You'd have freighter ships with no navigators and the most basic of warp drives making a bunch of short jumps of only a few light years each time, cumulatively slower than a normal jump but you dont need a navigator and its still fairly safe.

 Grey Templar wrote:
I believe they are definitely a thing. Planets which are physically close enough to each other for sublight speed to be practical will do exactly that.

The thing is that most planets are not going to be that close. But Warp drives aren't exactly difficult to craft, and if you are making short jumps you don't really even need a navigator. You'd have freighter ships with no navigators and the most basic of warp drives making a bunch of short jumps of only a few light years each time, cumulatively slower than a normal jump but you dont need a navigator and its still fairly safe.

A big consideration would be fuel. Do warp drives use more fuel than conventional propulsion? I can very easily see something similar to the initial adoption of steam power - bulk cargo ships still used sails because they were slower but cost much, much less to operate.

I would think in-system traffic would not bother jumping unless there was a reason to basically teleport into orbit.

Given the infamous passage on refueling warp drives, it doesn't seem that warp drives need to be refueled very often so fuel costs might not be too bad even if it was expensive.

In-system traffic definitely does not warp jump unless desperate- warp jumps around planetary bodies are incredibly dangerous due to the gravity distortion. That is why fleets and ships almost always arrive at the edge of the system and travel in at sub-light speeds.

System ships do not normally carry warp drives at all because they couldn't really use them and therefore can save space and cost.

On the topic of warp-incapable ships, I have this vague image in my brain of smaller imperial ships riding into the warp alongside larger warp-capable ships.

Are warp-capable ships able to bring ships without warp engines along with them? Or does entering the warp require one engine per ship?

 Wyldhunt wrote:
On the topic of warp-incapable ships, I have this vague image in my brain of smaller imperial ships riding into the warp alongside larger warp-capable ships.

Are warp-capable ships able to bring ships without warp engines along with them? Or does entering the warp require one engine per ship?

I do recall this being a thing but cannot think of any specific examples.