On Tue, 20 Oct 2009 14:38:53 -0400, Jeff wrote:

We imagine two boats one leaves Throgs Neck one hour before the current
change at Throgs. He does 6 kts through the water. Is there a later time
at which another boat can leave WITH the current also doing 6 through
the water where the second boat will arrive at Verrazano Narrows at
exactly the same time?

No.

The boat that leaves first will always stay ahead because they will be
in stronger ebb current first as they approach Hell Gate, and at no
time will the adverse current exceed their boat speed of 6 kts, so
they will always continue to make forward progress.