The problem is the game doesn't list encumbrance for some items. I'll demonstrate this with a few examples.
The players in a YT-2400 raid a pirate base. The pirates just hit a huge shipment of weapons, and they haven't moved them yet. Inside the base there are 9 crates of weapons. How many can they fit into that YT?
Answer: We don't know, really. We know the encumbrance capacity of a YT-2400 is 140 (whatever units 140 is said to represent). But we don't know how much a crate is. Obviously, the easy answer here is for me the GM to just assign some sort of random value of say 20 to each crate. Meaning 7 crates can fit on the YT. But I'd rather have a value.
Inside that pirate base is also 7 speeder bikes. How many speeder bikes can they fit into the YT?
Answer: Again, we don't know. There is nothing in the rules that tells me they can even put one in. The only blurb about putting vehicles in a starship is listed on the Retrofitted Hanger Bay (P. 271), and the RHB can only be put on vehicles of Sil 5 or greater. Meaning that YT can't even equip it. So does that mean you can't fit a vehicle on it since the RHB is what allows you to store vehicles on a ship?
A speeder bike is about the dimensions of a motorcycle in real life, except slightly longer. You can fit a motorcycle in the back of a pick up truck. So if you can't put one in the cargo hold of the YT, what can you put in there? What does that say about the cargo hold? It's less then the back of a pick up truck? And if that's true, how am I putting 7 crates of weapons in it?
Okay so assuming you can fit one on the YT, how many can you fit? The speeder bike does not list an encumbrance value for how much it encumbers something (I don't want to say weight, because that gives the wrong impression).
That pirate base is pretty well stocked. They have a cloud car too. Can that fit into the YT?
Answer: No? Why not? It is silhouette 2 just like the speeder bike. But we all know from watching the movies that a cloud car is significantly larger then a speeder bike. Logically you can't just roll one of those up the ramp. The lack of an encumbrance value for the cloud car itself is only one of the problems here. Logically, silhouette doesn't make sense sometimes.
Instead of a YT, the players chose a Wayfarer as the starting ship. It has a RHB equipped and they have inside the ship two Z-95s for two of the players to jump into when space combat starts to protect the ship. The Wayfarer has an encumbrance cap of 850 units. With two Z-95s already on board, how many crates of weapons, speeder bikes and/or cloud car can they fit into that transport?
Answer: See what I'm getting at here? Because we don't know what the encumbrance value of a Z-95 Headhunter ship, we don't know how much of the cargo bay is even in use. Compounded by the lack of an encumbrance value for the speeder bikes and cloud car, it becomes a guess for the GM to figure this out, instead of cold, easy to determine numbers.