Passing (or stopping someone pass) on a reach??

I think I've worked out what one problem is - the overlap doesn't stay parallel to the direction to the next mark, ds797, but to the transom of your boat, so as Brass says, when you turn too far you create the very overlap you were trying to avoid.

As Rupert says, regarding scenario 1 if you gain an overlap to windward of the boat ahead then they are entitled to luff you up head to wind as long as they give you room to do so.
In scenario 2 where you attempt to sail to leeward, while you are clear astern the boat infront can bear away to try and force you to overtake them on their windward side, however in the process of bearing away they may inadvertently create an overlap!

Ok are these statements correct.....?

1- If I'm trying to pass a boat in front, if I try to sail to windward of her she can luff up to head to wind (which I would have to also do to avoid collision).

2- If I'm trying to pass to leeward of her, she can immediately turn up to around 90 degrees to "block" me from passing that side.

3- Therefore the boat in front can basically weave around by up to around 180 degrees to block me from passing.

So the only way I could pass would be to head off way to leeward of her and establish an overlap some distance downwind of her?

Obviously the front boat "weaving" is not sensible for the front boat to do in a multiboat handicap race as the people behind will catch up, but if its a series and you need to finish in front of me it would be a usable tactic......

Just to make it clear to the OP, the rules allow a boat clear ahead to sail where they like. There is no obligation to sail a proper course but clearly it is in their interests to do so.

The rules only come into play when overlaps are formed.

If your proper course (ie, you'd be doing it whether the other boat was there or not) would be to luff in the lulls and bear off in the gusts, then you can carry on doing the luffing part of this even if you aren't in a position where you are allowed to luff the other boat for tactical reasons. You aren't allowed to bear away, though, if there is a boat to leeward which you will impede, so if you overtake a slower boat to windward, then catch a big gust (especially when flying an assy), you either have to rag it, swim or both...

If you are overtaking a boat to leeward and the wind drops, then you can alter course to suit. However, as it is likely that at least part of the wind dropping will be because you are in the lee of the other boat, you'd have to be pretty damn sure of yourself when taking it to protest, as altering course because of the other boat's wind shadow is not proper course.