Hmmm...interesting crossroad. Here we have pure fantasy juxtaposed with cruel reality. The average professional swimmer can swim ~3.5 m.p.h. Assuming this guy doesn't eat or sleep or anything else, and assuming he doesn't get tired or slow down at all, he could possibly do this in 3.5 months of straight swimming. Unfortunately, a live human body in oceanic water for more than three weeks will start to decompose. That does not consider other variables such as hypothermia or attacks by any of dozens of sea creatures whose backyard he would have to cross.
It is an interesting thought. However, the idea itself is flawed. If there were a way to do this, then in tens (or hundreds) of thousands of years of human existence, someone would have already done it. If this were a real thing Tom Hanks would be screwed. All he had to do was to jump in the ocean and swim for a few thousand miles. Who needs ships?
