A lot of time has been spent on tides/currents in the pre-race chatter. Evidently, some "narrows" are impassable when the tide/current is going the wrong way. Could allow boats to catch up or boats to extend leads. Timing is everything.
Seymor narrows. Google it, interesting place and it used to be way worse before they blew up a bunch of granite. I hope there is good footage of the passages through this section.