[Einzelganger]

For me it depends for the most part on what intresting targets a convoy has to offer. Other points will then be time of day, weather and what stage of the war one is in.

During the early years of the war when DDs don't have radar yet i usually keep contact by staying on the edges of visual range closely watching out for any DDs that might venture away from their normal course. However, as i like to wait submerged right infront of an approaching convoy i usually will loose contact getting into position. So, occasionally i will loose a convoy.

Later on in the war you'll have to start making estimates based on contact reports or contacts so as to get in a good position as staying on the surface in their vicinity isn't wise anymore.

Suprisingly, after each attack a convoy will hold more or less it's general course so even late in the war i will usually make contact again. Not sure if that's entirely realistic....