More thoughts on trading:
One of the ways to make the life of a trader more "interesting", is to make it so the player has to put together combinations of consignments of cargoes into a profitable trip. As it is now, each commodity takes up a fixed amount of "cargo space" for the market price, and that cargo can be sold anywhere the trader cares to dispose of it.
This is a way of abstracting the current "intermodal shipping container" [
http://en.wikipedia.org/wiki/Shipping_container], which are reusable. These come in nominal standard 20 and 40 foot long metal "boxes" (or "cans" in Sci-Fi space trading lingo): one 40 foot container is the standard unit moved between truck, rail, or ship. Two 20 foot containers are placed on a rail or truck "spine car" which keeps them together until they reach their respective destinations. These "half-cans" are generally the smallest container handled. Smaller packages would be packed into either a full or a half-can. A nominal 20 foot "half-can" has an internal volume of 1169 cubic feet (imperial) or 33.1 cubic meters (metric) [
http://en.wikipedia.org/wiki/Intermodal_container]. There are variation in these sizes and volumes, but this is merely to give an idea of general capacity. Remember, those are the volumes of a 20 foot "half-can". Roughly double that for the normal 40 foot "full-can".
The big advantage of using "cans" is that it standardizes the cargo size of the "commodities". But not all "commodities" are the same size and this can get forgotten. If a piece of "heavy equipment" takes up one entire can, then the market price is for delivery of one "unit" (which just happens to be "one can") of cargo. On the other hand, one unit of "boxes of boxes" is a "can" of boxes. A full can would be roughly 66 CUBIC meters of boxes. Assuming the market price is an abstracted "unit value" (i.e. $1 = $1,000), that is still a lot of boxes in even one "full-can" of cargo. Sectors will still need them (for packing commodities into "cans"), but not likely a repeating trade loop of an entire cargo ship's capacity worth. But "half-cans" leave "gaps" in a ship's cargo hold to fit odd lots into that may otherwise not appeal. That sort of "dribble" is what keeps those lesser profitable commodities from becoming urgent shortages and surpluses in the supply/demand market.
Also, many "cans" contain "mixed lots" of commodities destined for the same end-point. (Think of "household goods" for a family moving to another sector, or a consignment for a department store or laboratory.)
The consequence of thinking in terms of capacity is that a trader then has to juggle current available capacity with cargo profitability. It's extremely easy when all the cargo is going to one destination: pack the hold with the single most profitable item and sell everything at the destination. This is the economic model in use now, and the only really practical one when starting out. But most cargo is not going to just one port. The port itself is merely a transhipment point. Trader ships are "space trains" hauling loads of "cans" from one point to another. If the destination is 8 sectors away and the trader can only jump 2 sectors at a time, then the "running costs" of docking fees and re-supply at the 3 intermediate stops eat into the available cash until the payday at the end of the run. It normally will make sense to leave at least some room for cargo bound for the intermediate stops, especially if tight on cash to begin with. But until contracted, profitable "long hauls" become available, this will not be a popular course of action.
The game already uses the concept of "cargo space" (e.g. "full-cans"), and variation in how much certain items take up. The current problem is that it is unknown how much cargo space is required for each item until after it is "bought". The careful trader would need to buy one of a commodity or item, and then track how much cargo space it took up. It's not clear if "half-cans" are already in the picture, as all that is given is the amount of remaining available cargo space (which may always be rounded down, giving a false picture of actual requirements). The "shipping specialist" skill suggests this capability is being abstracted. But while an increase of available cargo space increases profitability, it doesn't increase interest in the trading game. Making the default assumption that one unit of cargo space is a "half-can", thus allowing half cargo space units, increases the possible combinations without changing the remainder of the game. But leaving the assumption "as is" and changing the size of various commodities can have the same effect.
To increase interest in trade, there is a need to have two kinds of cargo to be available: for sale, and for delivery.
The current market place is a "for sale" market, which encourages the trader to buy commodities on speculation of being able to make a profit at a specific destination. By having varying quantities available at each port, the profitability question becomes less "cut-and-dried" than "buy a full load of this here and sell it there".
"For delivery" could be implemented (as suggested by Waltorious) in the form of "quests". Though ideally this would be in the form of multiple quest offers of specific quantities going to different sectors, with specific "delivery by" dates. Then the trader needs to plan out the route and juggle capacities at various stages along it. The trader would not be "buying/selling" the commodities, but rather earning a "Transportation Fee" of a fixed amount: a "sure thing" rather than a speculation, that hopefully leaves a profit after running expenses. Not generally considered the way to "get rich", but usually a sustainable, slow growth method. That will encourage leaving some free space for "spec loads". Some smaller ships may not have the available capacity to take on many delivery quests, and remain forced in the speculation mode. OTOH, such small ships should be more flexible in taking multiple high-profit, small volume loads to different sectors. More like "large cargo space ships = railroads, small cargo space ships = trucks".
-Dubious-