I dont want to get into a slanging match, I will just make my point and then dissapear.
from wikipedia
Type 214: range 19,300km, endurance 12 weeks, 2310 km on fuel cells,
Collins: range 20,000km, enurance 10 weeks, 890km on batteries.
Conclusion, from endurance, type 214 comes out slightly better. Probably due to being a more modern design, using AIP.
Underwater refuelling, it could be done at say 50m depth. The vessel that went down 12km to the ocean floor used petrol as it's primary means of ballast. The petrol was not kept in a pressure hull. (they had tonnes of it). Submarines in WW2 pumped deisel from outside the pressure hull to inside it, because the fuel tanks were external.
Now some may argue that the 214 range of 20,000km is not long enough. Perhaps a slightly enlarged 214 or more modern 214 would have longer range still?
As to 'non experts' commenting in this thread, for starters there is nothing in the website that says you must work in the field to have permission to post, my understanding was that this forum was open to all.
I have personnally spent an entire day reading a book on the Collins Class submarnine project. I would like to think I know more than the person on the street, but of course I know much less than the experts. My job is paint chemisty, we can talk about that if you like, I know a lot about that...
From the book, and other sources, I gathered the idea that there was a significant gap between the retiring of the Oberons, and when the Collins were really up to speed. What would have happened if we were in a bad war during that time? my guess is that we would have been stuffed.
I am not saying that the 214 will be a better sub than a purpose designed australian sub, but that when the time comes to get a replacement getting the best commerically off the shelf conventional submarine in the world, might be something worth considering. The 214 in ten years from now, might be much better than the 214 that can be had now.
Reading between the lines, I get the feeling that the Navy wants a submarine that can go up to China and 'deter' them.
The risk in developing a new class of subs just for Australia, is that they will cost a lot more (read double the cost) and run the risk of technical challenges delaying it many years. This is what happened with the Collins, the same could happen (it may not) with the replacement sub.
Would you like to elaborate on why refuelling from a towed mini-sub which is carrying fuel in a non pressurised vessel would be difficult. To me it just seems to be a question of hoses and pumps. Not super easy, but should be doable. Refuelling at 30m to 50m underwater might be relatively simple.
As to nuclear, my guess is that it would cost a fortune. Do we really need it? Perhaps if the idea is to protect Taiwain, but to protect Australia, hmmm. In 10 years fuel cells are likely to be even better than they are now.
Getting back to 'non-experts' making the occasional post. Remember 'sparky', one thing he advocated was simpler lighter COIN aircraft, he also advoated light armourned tracked vehicles. What is happening several years later... the US air force is looking at turboprop light attack aircraft because they are cheaper to run compared with fast jets. The British Army is building new 'light tanks' based on the Scorpion tank hull (albeit with 30mm cannons, not 76mm) and not building the 30t to 40t FRES projects they were contemplating. So perhaps in these 2 things Sparky was right. My point is that a 'non-expert' can sometimes have valid things to say.
For the record, I think sparky was a bit rambling and slightly off balance, but he seemed a nice enough fellow and well intentioned. He got a lot of stick because he did not come from a military background.
long live Sparky!