I think you are under a misapprehension,aog.
As has been explained, all three races (the men's, women's and men's reserves) will take place on the same day, over the same course, in the same direction. That is to say from Putney to Mortlake ("upriver") with the benefit of the incoming tide.
As I explained in an earlier question (probably about this time last year when the question of rowing being "elitist" was aired) I have rowed extensively on the Thames. Most of my rowing was done a little farther west than the Boat Race (mainly on the stretches between Barnes, Chiswick, Kew and Twickenham, depending on the tide). I can say that to row decently in the middle of the river, as the university eights do, is all but impossible against the tide. We had to "paddle" as close to the banks as was safe when moving against the flow (thus minimising the effect of the current) in order to get to a point where we could turn round and have a good run with the tide. When doing this it was very welcoming to row inshore of Brentford Ait (where the gasworks were) as the island provided particular shelter from the tide but you needed a knowledgeable cox because there were a fair number of nasty obstructions in that dark and overbearingly dingy stretch.
Clare Balding has a point when she says why she has forsaken the Grand National this year. As she says, this is the only time it will be the first occasion that the ladies have been granted equal billing to the men, whereas the Grand National will still be around next year.
At least, unlike in tennis, the ladies will be rowing over the same distance as the men. I wish them luck. I rowed twice competitively over the Boat Race distance in the schools "Head of the River" race. That race is run over the same course but in the opposite direction to the Boat Race (with an outgoing tide). We were a good eight (especially the second time I took part when we finished eighth) but in well over twenty-one minutes. The Schools' record now is just under 17 minutes and the University Boat race record is 16 minutes 19 secs.
As I said, I wish the ladies luck. Over four miles is a fearful distance to row on a tidal river virtually flat out (Olympic events are held over a mere 2km - about one and a quarter miles - usually on a calm lake). After ten or twelve minutes you think you are going to die and five minutes later you wish you had. So all credit to the Ladies. At least, though, they only have one other team to beat. In the "Schools' Head" when I took part there were well over 200 !!