All dependent on distance, you decide.
Conduct some further soundings and get a generalised course and speed plotted for your target. Surface for a set period of time, then submerge and sound again to re-establish the targets course/speed and distance.
Try not to be surfaced when you enter visual range. Some warships are n00bs and some are veterans.
It is however, during early war, possible to be surfaced (decks awash) and be within 1500 yards of convoys without being detected.
You make the call, Captain.
