From the symptoms you are mentioning I wonder if too fast expansion is the cause? Having little or no fuel for the private sector at your ports is often a symptom that private shipbuilding has been floushishing for some time since they load their tanks when first built. The demand for steel can also be explained by the need for all those fuel cells and cargo bays plus it is now consumed by colonies.
Having a large galaxy will compound any fuel problem, you are right about that. Restricting large spaceports probably doesn't make much difference as I think that the civilians will still want to build the same number of ships (=same fuel required). The major cause of civilian shipbuilding is colonies. Perhaps try a game with a much more harsh economic start, or otherwise try to slow down your expansion? Keeping your early empire compact also helps - more freighter trips from shorter journeys.
I have noticed that the rest of the galaxy 'steals' my fuel (well they pay but I wish I could close up shop sometimes ). Last game I thought I was cruising just after having got to Gerax drives (@ 2 colonies), with close to 200k caslon banked... then within the space of a year close to 150k of it was sold, and my expansion sucked up another 30k (mainly filling up those empty freighter tanks the first time around). Steel and lead also seem to be bought out a lot...
When you say plenty of hydrogen and caslon mines what are we talking? Personally I find that at least half of my mines early and upwards of 2/3 of them later need to be fuel sources.
A final thought - you haven't recently discovered improved fuel cell technology have you? This can lead to severe shortages at all spaceports for a while as all the freighters try to fill up their now larger bellies.
That's a very interesting reply thank you. In my earlier post I wondered whether I had expanded to fast. On the other hand, I'm playing with a sector colonisation limit of 1.2, which tends to motivate me to colonise all new star systems I can. Having said that there are a large number of planets I could colonise, but haven't. My other worry is that if I don't keep colonising I'll end up falling behind. I'm way ahead of the other empires on population and economy, but they always seem to keep up with me, or often ahead, when it comes to colonisation. I worry that their extra colonies will come back to bite me later in the game. I still don't really know how many colonies you need to win this game. Perhaps I should try playing a game with just, e.g., 6 colonies, and see where that gets me (probably face down in the dust with what passes for a foot on the back of my neck!)
So far as mining is concerned, I'm sure I have a lot of hydrogen and caslon mines: I really did prioritise them this time.
I have discovered some additional fuel cell tech, I think (I'm away from the game right now). Anyway, I'm over half way through the tech trees, so I must have done. I design all fleets myself, and I have probably given them the latest designs. Maybe that's something I need to change - restrict the range of the private fleet, to reduce its fuel consumption.
I only partly understand what you say about the need for steel. Yes, I understand that the private sector needs steel to build its ships. But it's not actually building the ships at present. Does the need show, even when the ships have not yet been ordered?
I think I may start again, taking into account some of the things you have mentioned, but there's still something I don't understand. My economy has masses of resources sitting at mines, and it has a massive fleet capacity which is largely well-fueled (for now). So why are the freighter moving around with less than a 10th of their full cargo capacity?
Anyway, once again, thanks for taking the time to reply.