Conventional submarines of the time, such as the escorting P 614 and P615, could sprint at 8 kts underwater but only for a few minutes before draining the battery. Their normal submerged speed was closer to 3 kts and their top speed on the surface was only 10 kts. In the meantime, the Tirpitz could make 30 kts and stand off 18 or 20 miles while bombarding ships with her 15" guns. Her sister ship Bismarck sank HMS Hood at a range of 14 miles.
The top speed of P611 class boats was specified as 13.75 knots surfaced and 10 knots submerged. Same conclusion, though.