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ship cargo hold conversion and correction


Starfinder General Discussion


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Pathfinder Adventure Path, Starfinder Adventure Path, Starfinder Society Roleplaying Guild Subscriber

Ship construction rules for freighter, meaning expansion bays converted to cargo holds has to be off.

I have to assume that for the game, bulk freighter and heavy freighters, etc., still are relatively small ships. Otherwise the cargo hull 25 ton capacity limit is way to low. On page 295 of the CRB, a bulk freighter has 10 expansion bays. A heavy freighter has 8 expansion bays. Accordingly to page 299, a cargo hold "can contain approximately 25 tons of goods." Size limits (volume) are based on merging cargo holds, not capacity. So an unmodified, basic designed, bulk freighter, and heavy freighter can only carry 250 or 200 tons of cargo, respectively. This has to be incorrect or the size of the ship is very small.

Why? A "Handysize" ocean bulk carrier ship (in real world) can transport 10,000 to 35,000 metric tons of deadweight. Ignoring metric tons vs. US tons (a difference of only 240 pounds), this means that the smallest ocean going freight carrier, a "Handysize", has 400 to 1,400 cargo holds on it.

I think a zero-G bulk freighter should have massive cargo capacities. Unless these are considered small ships and atmosphere capable, I cannot see such restrictions. Also there has to be considerably more massive cargo haulers not yet disclosed. Ok, I get this.

Also, if you convert the expansion bays to crew quarters, we are only looking at a max of 60 passengers per expansion bay. As we know, this is extremely small. Also, just to play with this, a 2017 Dodge Ram truck has a max towing capacity of about 5 tons.

While the rules say "these size restrictions can be overridden at the GMs discretion," I propose the following:

My proposition:

A 20-foot cargo container seen in modern day can carry 21 tons of goods. A 40-foot cargo container can carry 25 tons. They are build for different purposes.

So I modify one cargo hold from weight to volume and make the single cargo bay size equivalent to eight 20-foot containers stacked 2x2x4, so that 8 containers can fit I a single cargo hold. This also allows 4 40-foot containers in the same bay at 2x2x1 (height, width, and then length). This preserves volume and modifies weight capacity. This also converts the cargo weight capacity to about 1600 tons/cargo hold. Much more acceptable, but still low.

Thus, a heavy freighter can "safely" transport and enter a planet's atmosphere carrying 16,000 tons, and a heavy freighter's lift capacity would be about 12,800 tons.

Also keeping this volume, we preserve the size of the cargo bay for conversion of labs, quarters, large and gargantuan size objects, etc.

Comments, criticisms? Anyone see anything wrong with this idea?


My biggest criticism has nothing to do with your analysis really, except to say that we should never be talking about tonnage in space.

We shouldn't use it at all even on earth, when we're talking about how much of something a thing can hold since that's volume and not weight. And there is no accounting of density.

Aerogel has a density of 0.16 mg/cm^3.

25 tons of aero gel would have a volume of about 3630 m^3 if I've done my calculations correctly.

A 20ft shipping container has a volume of about 40 m^3. Or roughly 1/ 90 the volume of the aerogel.

My point?

The numbers given to us are really meaningless.


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Have a similar issue with the expansion bays, they seems a little bit off.
I already thought about adding "special abilities" to spedcific frames (e.g. freighter frame = double the cargo hold capacity) to fix it, but it's still off.

I think the creation rules are more or less designed for tiny to medium starships, everything larger doesn't fit at all.
(A real world frigate can carry two helicopters, a med bay, life boats, multiple zodiaks... A starfinder destroyer (twice the size) hardly managed to get one shuttle a med bay and some storage).

I thinks it's the usual "game mechanic vs. real world" thing. :)

For myself I decided to wing most of the big ships player will never fight again and only use the ship building rules for enemies the player will fight (at the moment).


For wet navy cargo capacities the term "ton" is a volume measurement, I believe 40 cubic feet, not a weight. So on a ship a ton of feather and a ton stone weigh different amounts but take up the same amount of space. And space is the important measurement in a ship hold.

The size of each ship is listed. A heavy freighter weighs 150-420 tons and is less than 800 feet long. It is capable of atmospheric flight. The Bulk freighter is about 3 times that size 420-1200 tons and is not capable of atmospheric flight.

To insert reality into this, there is probably little reason to ship large amounts of anything. Food might be the bulkiest items. Otherwise, processing ores and such on planet and shipping finished products is cheaper, especially with automation.

Another caveat, these are PC available examples. As with the Colony ship discussion, a truly huge shipment of anything is very likely to be a plot point, not something the PCs run around in their entire careers.

Claxon wrote:

My biggest criticism has nothing to do with your analysis really, except to say that we should never be talking about tonnage in space.

We shouldn't use it at all even on earth, when we're talking about how much of something a thing can hold since that's volume and not weight. And there is no accounting of density.

Aerogel has a density of 0.16 mg/cm^3.

25 tons of aero gel would have a volume of about 3630 m^3 if I've done my calculations correctly.

A 20ft shipping container has a volume of about 40 m^3. Or roughly 1/ 90 the volume of the aerogel.

My point?

The numbers given to us are really meaningless.


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Pathfinder Starfinder Adventure Path Subscriber

I went on a couple rants in various threads in this. So, a couple things:

Tonnage IS useful for shipping, for similar reason it is on earth (I speak as an intermodal shipping coordinator, btw). Fuel needed to ship and the size of the engines needed to move the mass (both accelerating and "decelerating") are probably still considerations even in zero g. Also even in ocean shipments displacement is a thing that needs to be tracked. There's a few pictures around of ships that ran aground in a harbor or brackish water because they calculated their displacement in saltwater, not fresh water.

Based on the average commodity weight that actually gets shipped in containers, I pegged our SF cargo holds at equivalent to a 40' container, or roughly 3000 cubic feet (I think I multiplied my last estimate incorrectly, oops, but I happen to be at work right now so I can check my math). It is technically possible to get 25 tons in a container half that size, but it depends on commodity. Also I hate dealing with those containers professionally so I refuse to acknowledge them in game.

A cargo hold that size actually works for smaller ships, but the number of expansion bays does not scale properly with ship size. So we have "bulk freighters" that could not fully stock a costco because they don't want to have players running around with ships that have 100 or 500 (1500 for a pure cargo hauler is not unrealistic, tbh) expansion bays like the bigger ships properly should.

I'd say quintupling the number of expansion bays on bigger ships might be more accurate, but limit the number of force multipliers like fighter bays to no more than the listed expansion bays.


EC Gamer Guy wrote:

For wet navy cargo capacities the term "ton" is a volume measurement, I believe 40 cubic feet, not a weight. So on a ship a ton of feather and a ton stone weigh different amounts but take up the same amount of space. And space is the important measurement in a ship hold.

The size of each ship is listed. A heavy freighter weighs 150-420 tons and is less than 800 feet long. It is capable of atmospheric flight. The Bulk freighter is about 3 times that size 420-1200 tons and is not capable of atmospheric flight.

To insert reality into this, there is probably little reason to ship large amounts of anything. Food might be the bulkiest items. Otherwise, processing ores and such on planet and shipping finished products is cheaper, especially with automation.

Another caveat, these are PC available examples. As with the Colony ship discussion, a truly huge shipment of anything is very likely to be a plot point, not something the PCs run around in their entire careers.

Claxon wrote:

My biggest criticism has nothing to do with your analysis really, except to say that we should never be talking about tonnage in space.

We shouldn't use it at all even on earth, when we're talking about how much of something a thing can hold since that's volume and not weight. And there is no accounting of density.

Aerogel has a density of 0.16 mg/cm^3.

25 tons of aero gel would have a volume of about 3630 m^3 if I've done my calculations correctly.

A 20ft shipping container has a volume of about 40 m^3. Or roughly 1/ 90 the volume of the aerogel.

My point?

The numbers given to us are really meaningless.

That just causes more problems because now we don't know what ton they were trying to use in their descriptions.


That is an interesting analysis. While I understand your example about salt vs fresh water displacement, I would never have consider it until I ran a ship aground!

AnimatedPaper wrote:

I went on a couple rants in various threads in this. So, a couple things:

Tonnage IS useful for shipping, for similar reason it is on earth (I speak as an intermodal shipping coordinator, btw). Fuel needed to ship and the size of the engines needed to move the mass (both accelerating and "decelerating") are probably still considerations even in zero g. Also even in ocean shipments displacement is a thing that needs to be tracked. There's a few pictures around of ships that ran aground in a harbor or brackish water because they calculated their displacement in saltwater, not fresh water.

Based on the average commodity weight that actually gets shipped in containers, I pegged our SF cargo holds at equivalent to a 40' container, or roughly 3000 cubic feet (I think I multiplied my last estimate incorrectly, oops, but I happen to be at work right now so I can check my math). It is technically possible to get 25 tons in a container half that size, but it depends on commodity. Also I hate dealing with those containers professionally so I refuse to acknowledge them in game.

A cargo hold that size actually works for smaller ships, but the number of expansion bays does not scale properly with ship size. So we have "bulk freighters" that could not fully stock a costco because they don't want to have players running around with ships that have 100 or 500 (1500 for a pure cargo hauler is not unrealistic, tbh) expansion bays like the bigger ships properly should.

I'd say quintupling the number of expansion bays on bigger ships might be more accurate, but limit the number of force multipliers like fighter bays to no more than the listed expansion bays.


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I'm glad to see some explicit numbers from an actual, professional background on how this could be handled, but it may be worth considering an alternate approach as well. Rather than inflating the number of expansion bays on larger ships to accommodate a larger number of cargo bays, it might also be worth scaling the capacity of an expansion bay with the size of the ship. The two approaches could even be combined, with larger ships having more expansion bays than they do now, and each expansion bay having a higher capacity as determined by the size of the ship. Extend this to guest quarters and you can now properly house suitably large numbers of people without it demanding an immediate, substantial BP and PCU investment.


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I think AnimatedPaper has the right idea but I would adjust some of the size.

As he (and others) stated the volume needed for a given weight varies. Finished goods like electronics may be less than 5 tons in a 40' container, liquids about half the volume. I have worked with a fair number of 30 ton steel forgings that would only take a fraction of a 20' container.

Given that the expansion bay cost for shuttle bays and hangars does not match the guidelines for item size listed in Cargo bay I think the size of an expansion bay should vary with ship size.Using the baseline of a single cargo bay holding Large (character scale) items I would say a Small (ship scale) cargo bay should be 4-6 5' squares and Medium ships up to 8 squares. For each ship size larger I would double the area. This roughly corresponds to Medium ships having 20' containers and Large having 40" containers. I would also suggest each ship size larger than medium could hold (character scale) items of one size larger. I would also say each adjacent cargo hold would increase (character scale) capacity by one category. Note that this only applies to volume, a colossal creature or vehicle would still require multiple bays (based on weight) even on the largest ships.


Pathfinder Starfinder Adventure Path Subscriber
Hithesius wrote:
Rather than inflating the number of expansion bays on larger ships to accommodate a larger number of cargo bays, it might also be worth scaling the capacity of an expansion bay with the size of the ship.

This actually works so well I would not be surprised to see it implemented in whatever supplement they put out on ships.


I agree, but the problem is dealing with certain types of expansion bay uses. If bay size scales with ship size, then does a Fighter Hangar carry more fighters on a bigger ship? Does it use more power?

I mean, a lot of the expansions, you could simply go with "the bigger version on bigger ships accomodates more people" or such, but for things like hangars, it does matter.


Pathfinder Starfinder Adventure Path Subscriber

The problem I think is that the tonnages for the ships are very badly off. Large ships on up probably should be about 1000 times larger in terms of weight.

Another thing to keep in mind that suprissed me was the danger of drift drive. In system drift has a 1% chance of encounters, travel to near space has >10%, travel to vast space has 25-50% encounter rate. That is insane common for commerce. This will make trade and trade vessels very different then ones found on Earth.

I would expect that all trade ships are armed and have security that is armed onboard. Also I would expect the truly vast shipping ships found in most sci-fi worlds would be less likely to exist given the dangers of the drift.


Not necessarily. For one, we don't know the *nature* of those encounters. How nasty an "encounter" is effects the logic much moreso than the likelihood. For another, larger ships don't just carry more cargo, they also can carry more arms and armor.

I do suspect there might be at least some tendency to use smaller ships in larger numbers for shipments into the Vast, though, just as a form of insurance. And in-system shipping might include a fair amount of STL transports, since in-system Drift jumps aren't much faster than just using the engines.


Pathfinder Starfinder Adventure Path Subscriber
Metaphysician wrote:

Not necessarily. For one, we don't know the *nature* of those encounters. How nasty an "encounter" is effects the logic much moreso than the likelihood. For another, larger ships don't just carry more cargo, they also can carry more arms and armor.

I do suspect there might be at least some tendency to use smaller ships in larger numbers for shipments into the Vast, though, just as a form of insurance. And in-system shipping might include a fair amount of STL transports, since in-system Drift jumps aren't much faster than just using the engines.

That's very true but it is something we should keep in mind when trying to compare to the real world. Cargo ships in the modern world don't have weapons of any kind and anything we could consider encounters are rare events.


C_Trigger wrote:
That's very true but it is something we should keep in mind when trying to compare to the real world. Cargo ships in the modern world don't have weapons of any kind and anything we could consider encounters are rare events.

Unless you were off the Horn of Africa (Indian ocean near Somalia or Yemen) in the early 2000's

I think there is another piracy area near Malaysia as well.


Also, the real world is not a comparable case. Its waters are fully mapped, more or less constantly observable thanks to satellite, and ultimately patrolled by naval forces that are basically the Hammer of God. They are safe, because they aren't the frontier.

This does not apply to basically *any* place in Starfinder, aside from directly around the major inhabited planets. If you are taking an STL jaunt from Absalom Station to Bretheda, probably the majority of the route is unobserved, and only inconstantly patrolled. And even if you set off an SOS, its hours minimum before any help can arrive, whereas hostile pirates or such could be departed in minutes with little hope of being tracked. Nearly the whole system is frontier, even in the "present". And this is exponentially moreso the case if your in the Vast.


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There is a very real piracy threat in the real world. The difference is the pirates tend to use small boats and board the target rather than shoot cannons from a ship.

In the real world you do not have constant satellite surveillance over every bit of ocean. At best it's available every few hours and only monitored if they are actively looking for something.

Naval patrols. At best during the height of Somali piracy there were a half dozen ships in the Indian Ocean. If a hijacked freighter got a distress call out it would still take hours to respond. During that time the hijacked ship may be able to reach a port. Recapturing a freighter is not easy. You can not shoot it with cannons or machine guns, you have to board it.


1 Cubic meter (35.3 cu ft)is 1 metric ton and weighs 1 ton when filled with fresh water.

Spoilers:

The sample ship in the first adventure path has 2 cargo bays each with 1125 sq ft and with an 8' ceiling means 9000 cubic feet(254 cubic meter) capable of carrying 254 metric tons of cargo for a total cargo capacity of 500 metric tons. For these comparisons, a metric ton (mass) of fresh water weighs essentially 1 ton (weight).

So a medium ships expansion bay (cargo) should be able to carry 250 tons.

A small shuttle with 2 cargo bays has the same cargo capacity as a medium ship with 2 cargo bays.

1 cuft of fresh water weighs 62.43 lbs so 1 ton of fresh water is 32 cuft. 25 tons of fresh water is 800 cuft. This is a cargo bay 8'tall by 10'x10'). Not a very big bay and not born out in their sample ship diagram.


While using the density of water works well for determining displacement of a nautical ship most cargo requires a greater volume per ton.

As others have so wisely stated increased mass requires increased engine power. This is even more important in space. Unlike a nautical vessel you need a lot of power to stop or even steer a space ship.

Is the sample ship in the adventure path a Medium size? Does the AP mention cargo mass being different than 25 tons? The size you list works out to 45 squares. Using that size a bay would be 5 x 9 squares. An Explorer with 4 bays this size, 2 wide by 2 high, would be about 1/3 cargo space if max length. A Shuttle with 3 bays, 2 wide x 1.5 high, would be about 3/4 cargo space at max length.

Using the 5 x 9 square bay from above you could fit two Gargantuan items in one bay. That is way larger that the default.

Yes a 10' x 10' cargo bay is quite small but not unreasonable for a Small size ship. I previously suggested in this thread that a small ship should have a 4-6 square cargo bay. That size works well based on listed lengths and also for a common (6 person) quarters. The size also allows large (personal scale) objects to be carried. A slight revision to my suggestions, using 6 squares at small and doubling each ship size class makes a Huge ship cargo bay 48 squares. If you use the default large carried object for small and Medium hull ships and increase by one for each hull size larger (Hull size +1, min large) that makes a Huge ship capable of carrying Gargantuan objects. The cargo bay from the AP is about what I suggested for an Huge ship.

I'm not totally convinced cargo Mass should be increased with Hull Size. Logically doing so should reduce max speed or require extra power. The main advantage of extra space is the ability to transport bulky cargo. While wheat and corn are slightly under the density of water other important food stuffs like malted barley are about half the density. Consumer products also tend to be packaged several times they actual size.


I used water since all mass measurements are related to the specific gravity of water. Using water makes 1 cubic meter equal 1 ton, good for mass to volume measurements.

The sample ship is medium.

Yes, 10x10, 25 tons is perfect for a small ship.

Doubling isn't enough. I would recommend increasing volume by a factor of 8 for each size increment - doubling every dimension.

If you don't increase cargo mass for a larger ship then they need to give larger ships more expansion bays.

Larger ships have more space available and more powerful engines why wouldn't you then also increase cargo capacity?

Cargo is the reason for a freighter. A huge freighter has 10 bays, a larger freighter only has 8 bays. The huge ship cant land so like likely needs a shuttle bay taking 2 bays. Therefore realistically a Huge freighter carries the same amount of cargo as a Large freighter. Since the huge freighter requires more than 3x the crew, why would the huge freighter get built? The large freighter does exactly the same thing for less cost. Even if you remove the shuttle bay, the Huge ship only carries 50 tons more cargo than the huge. How is that ever cost effective?


I used the density of water as a base as well but increased the area by 40% to allow room to move and that size also works well for quarters.

Doubling floor space still allows room for cargo of size (Hull Size +1) which is considerably more lenient that what the book suggests. Two adjacent bays could fit size (Hull Size +2) cargo.

Starting at 4 squares for small and quadrupling (2x each direction) per Hull Size makes a Large ship cargo bay big enough that you could argue it should be able to install a shuttle bay (for 2 expansion bays)

Using a cubed rule for volume would also have a large effect on hull size and cost if you used real world concerns.

Increasing cargo mass too much also messes with drive cost. Increasing Hull Size roughly doubles BP cost and the PCU increases by 30-50%. If you doubled mass each size over medium it stays fairly balanced. If you went 4x then a single large ship bay would equal most Medium ships.

As discussed elsewhere, increasing the number of bays for ships the PC's could modify would break play balance. A Large freighter could easily have every expansion bay they wanted plus cargo and quarters.


if its any help... GURPS Traveller, had 1 displacement ton of cargo space
weighing 7 tons of mass for various calculations.. a displacement ton being 14 cubic meters


It doesn't matter what we use for a weight mass-index. The issue is that a shuttle with 3 expansion bays fits into 2 expansion bays. There needs to be a multiplier for cargo capacity of a bay based on ship size.

Then that leads to the larger problem that expansions (labs, etc) are bigger on larger ships but there should be bonuses applied for the larger spaces, or larger expansion slots should allow for multiple expansions to account for the larger size.

As for expansion bays on huge craft: we know they are at least 60' long, and very likely longer (a 120' shuttle fits in 2 bays so the bay must be at least half the length of the shuttle).

If all expansion bays are the same size how does a shuttle fit into 2 expansion bays?


Dark Sorcerer wrote:
If all expansion bays are the same size how does a shuttle fit into 2 expansion bays?

My answer to this riddle is this...

One Cargo bay is 20 feet tall (twice the avg height of a room) with 25 sections of 5-foot squares.

Two cargo bay linked is 40 ft tall with 625 sections of 5-foot squares.

My point is if you add another bay to it then Square the Volume of the room, don't just connect the two like taking a wall out.


Rahod wrote:
My point is if you add another bay to it then Square the Volume of the room, don't just connect the two like taking a wall out.

Using your method a hangar bay would be at least 80' high and 309,625 squares. It would be a square 3125' on a side yet only hold 8 fighters of 60' max length.


I think the best answer is to have bays be different sizes by ship size.

If we take a medium ship bay to be 20'x20'x10', this will hold 2 TEU containers side by side and hold 25 tons. A TEU container is 20'x8'x8.5' and weighs 25k lbs fully loaded.

A 300' medium transport (150 tons) with 5 expansion bays (4 are cargo) would hold 100 tons (8 TEU). A Boeing 747-8 is 250' long, narrow and holds 154 tons. Not an unreasonable comparison.

Then for the large bay we double the dimensions to 40'x40'x20'. Each of these bays is 4 small ship enhancement bay equivalents and hold 400 tons of cargo (16 TEU-double stacked). Or each can have 4 enhancements, not necessarily all the same.

An 800' large freighter (420 tons - needs to change) with 8 expansion bays (all cargo) can hold 128 TEU for a total of 1600 tons of cargo.

The Huge bays are each 80'x80'x30', hold 1200 tons of cargo each or 16 expansion sets (96 TEU - triple stack). Two of these bays are large enough to hold not only a small shuttle, but also the supporting equipment for them.

A 2000' long bulk freighter (1200 tons - needs to change) with 10 expansion bays can have a shuttle bay (2 expansions) and 8 cargo bays for 96000 tons of cargo (768 TEU). For reference: A 1000' long ocean Panamax freighter holds 3200-5100 TEU.

The Gargantuan bays are each 160'x160'x40'. A rules change would make one of these big enough for a hangar of 8 fighters.

So theoretically a 15,000' long carrier with 10 bays would be able to carry 80 fighters, not unreasonable when you consider a 1000' aircraft carrier has an air wing of 85-90 aircraft the smallest of which is 56'long.

Compare this to a 15000' carrier that can carry 8 fighters and 150 tons of cargo in the remaining 6 bays (the limit of the current rules)...

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