On page 119 of the DMG is a table of various air/sea craft. What I'd like know is how the wight works out, specifically for the airship, but also for the others.
It states that the airship has a cargo capacity of 1 ton (2000lbs), and a passenger capacity of 20. The way that the crew section below is written it appears that crew take up passenger space, so there can only be 20 people on the airship at a given time. Assuming that these are humans with average weight (155lbs) this comes to 3100lbs of crew/passengers. Assuming that some races are heavier than humans, it seems like a nice arbitrary total cap on passenger/crew weight is around 4000lbs. This would make the overall carrying capacity of the airship 6000lbs or 3 tons. Of course, the 4000lbs doesn't account for any weapons/gear any of them are carrying.
The reason I'm trying to figure this out is that I'm wondering what kind of conversion you get between cargo space and passenger space. Can you carry another 10 passengers if you have no cargo? can you carry an extra ton of cargo if you have the minimum required crew?
On top of this, is the minimum crew added to the max passengers instead of subtracted from it? This would result in an extra 1.5 tons of carrying capacity.