In reality, BDU micromanaged the u-boat fleet with a capital M.
Unfortunately, the virtual BDU in the silent hunter series is nowhere near as dynamic as it should be even for a game.
In reality. A u-boat commander would be told to reach a specific area where other boats would be patrolling. He would then be provided with contact reports and instructed as to when to proceed with the attack
For example "stalk convoy, provide regular updates on their position, wait for other boats to arrive."
This could go on for days
Suddenly the order "commence attack at dusk" or something similar would come in
If conducted properly, you would have a few boats all attacking the convoy at once thereby inflicting enormous losses.
Perhaps, given the limitations of our rather unrealistic BDU, the best thing to do is decide what your favorite hunting grounds are (rockall banks, Irish sea, American east coast etc) and then hunt there routinely.
If you run out of fuel at sea... You're hosed. That's it, your done. You can refuel at supply ships or supply subs depending on your chosen mods (GWX3)
Edit: if you run at about 9 knots, your range significantly improves. Just keep an eye on your remaining fuel.
I generally head home at around 50% remaining
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