I would agree with the premise that a starvation strategy is viable and is indeed the only realistic one for the Germans in either world war but this thread has turned in a caricature of trying to argue that said starvation strategy is easy. When in fact it was far from easy and very resource and personnel intensive with enormous attrition rates among those personnel, something like 75% did not return from their last patrol in World War 2.
In WW2, resources needed for a succesful starvation strategy via U-boat and surface offensive are insufficient - unless the war goes on and on as UK-Nazi Germany fight, and even then it would take years. There's no way Germany can knock out Britain out of the war before DEC 1941. If by hook and crook the US stays neutral, not giving lend lease and credit, Britain is knocked out financially rather than by starvation. If the US goes in a lend lease approach, there's no way Germany can realistically knock out British sea lines of communication.
More viable strategy would be to invest more in Luftwaffe and just enough in Kriegsmarine to keep the convoying going on, with perhaps a tint to littoral warfare in British East Coast. Luftwffe could bomb ports, though. The German resources invested in Kriegsmarine were rather large and mere numbers do not tell all the tale as the Kriegsmarine sucked some of the best manpower and best industrial efforts.