@ Captain J. Borne: Running at the most economical surface speed (~7 knots) except when absolutely necessary for offensive/defensive purposes, the range of a VIIB in the game is... I dunno exactly, but a lot. Around 30,000 km IIRC, maybe a bit more. Even based out of a North Sea port I've been able to spend upwards of 5-6 weeks on patrol in the Western Approaches and still get home with plenty of fuel to spare once I ran out of ammo.
On one patrol I made it as far south as Las Palmas and after 7+ weeks out I still would've had enough fuel to get back to Wilhelmshaven if I'd turned around and gone straight home with no diversions - it would've been cutting it close, but the only reason I refueled there was because the hunting had been so good in that area and I wanted the option of hanging around a bit longer.
Unless you're using Commander to assign yourself patrol grids that are historically inaccurate for your u-boat type and flotilla (i.e., too distant from your base to be at all "doable" in any realistic way) or running at a very uneconomical speed for the duration of your patrol, there shouldn't be any issue with getting to the grid, completing a 24 hour patrol (at the very least) and getting back to base.
Just hitting the assigned grid and staying 24 hours and then going home - even if I sailed all the way back - wouldn't be realistic enough for me, even if I managed to use up all my ammo in that short a time. Which would be highly unlikely, unless I happened on a convoy and managed to fire off everything I had at it.
Besides, I keep patrol logs and teleporting home would make the times and dates look really weird. There's no way I could sink a ship with my last torpedo in grid DH73 and be back in base a few hours or minutes later. That's one reason I always sail back to within the required "docking distance" from the place where I'm going to dock. Or at least to within a few hours distance from it.
But, that's my personal preference. I can tell you though that if you are beaming your boat back to base after 24 hours in your grid because your patrols are too uneventful, you are probably gonna have a lot of very short, uneventful patrols. What frontboots did, mostly, was hang around their assigned area and wait for an enemy ship to appear so they could engage it, or for someone else to report enemy shipping close enough to be intercepted. Most of the time was spent waiting and searching, not actively engaging the enemy.
And, yeah, if you consistently run at 1024 TC, you are probably going to miss contacts. And eventually get yourself killed before you know how it happened.
