you might be able to use this...
So here's the deal...
I'm working on a plug-in that will allow you to customize the jump drive on your ship. What I wanted was for there to be different types of jump drives available. A class 1 jump drive allows to to travel from system to system in 1 day, a class 2 jump drive allows you to travel from system to system in 2 days, and so on, up to a the slowest drive, a class 4 jump drive, which allows you to travel from system to system in a sluggish 4 days. It sounds simple enough in concept, but it was very difficult for me to impliment.
Since EVN, by default, lets every ship jump from system to system at a preset number of days, the first thing I did was standardize each ship to take 4 days in order to jump from system to system. I did this by creating an outfit that 'increased jump days mod' by '-1'. Then I made each ship start with this outfit in the appropriate quantity in order to make it take four days to jump from system to system. The problem is, this outfit would show up in your 'extras' field during play, and I didn't want that. So I just blanked out the name field for it, and the 'extras' field showed 'no extras'.
The next thing I had to do was prevent ships from jumping that didn't have a jump drive at all, so I set each ships' fuel level to zero.
Next I created a jumpdrive outfit and a fuel tank outfit. There was a require on the fuel tank outfit that required you to first have a jump drive in order to purchase fuel. This way you had to buy the jump drive before you could jump from system to system. The problem was, someone could sell the jumpdrive, and still jump from system to system. Amneth, who has been very helpful for me, suggested I simply not allow the jumpdrive to be sold, but since I decided I wanted different versions of the jump drive, this would not work. I had to make the game force you to sell all of your fuel in order to sell your jump drive. Here comes the innovative part.
I made the jump drives into fighter bays, and the fuel tanks into fighters! First I created a junk ship that I called UNUSED. Then I made a 'class 4 jump drive' outfit that was essentially a fighter bay, and a 'fuel tank' outfit that was essentially the UNUSED fighter. In order to make sure you couldn't launch, or even see the junk fighters I made the launcher be a primary weapon (so it wouldn't show up in the secondary weapon menu field) and I set the bit 'cannot fire unless key ship something or other' so you couldn't actually fire your fuel tanks (which might be a cool addition later on). In addition to being weapon: UNUSED, I set each Fuel Tank (fighter) to also be 'added fuel: 100'. I also set each class of jump drive, in addition to being a figher bay for UNUSED, to jump days mod: -1, or 2 or whatever, so that the class 1 jump drive was -3, and would reduce the number of days for a system jump from the default 4 that every ship has, to 1 day. Now each time you upgraded your jump drive you would first have to sell off your fuel tanks. It works perfectly!
The result is I now have 4 jump drives, all mutually exclusive by putting !Oxxx in the availability fields of each one, excluding the other types of jump drives. Each jump drive is uniform for all ships, and controls the number of days each ship takes to jump. Pretty cool, huh?