Thank you for the background, but my questions still stand on how to PLAY the game.
I think I have figured out my first question about the 2MF at the end of a Tack maneuver by looking at the reference card. When your Tack is done you are in fact only moving at 2MF in the new direction. You are then free to accelerate along your new course up to the maximum allowed by your sail setting.
As for my second question concerning changes of speed, let me please make sure I have some things straight first.
Ships must expend all MF each Phase. That I've got.
A ship's maximum MF is determined by their sail setting (as modified by gusts, damage, etc).
So if I am generating 10MF I must move those 10. Easy enough.
Now if I choose to decelerate by 2MF I will be moving 8MF this Phase.
The question then becomes how many MF do I have on the next Phase? Am I still at 8? Or do I go back up to the 10 my sail setting provides?
My understanding is that I am at 8MF to start the following Phase because the wording of 4.4 first bullet point says, "she may decelerate each Tactical Phase until she expends no MFs". Therefor each Phase I can choose to Accelerate or Decelerate from my CURRENT MF. However, with reducing speed I see one subtle difference between the listed ways of doing it. If I choose to reduce speed by Deceleration, or by Backing Sail if a square-rigger (which I still don't understand why there is a full section about that because there is nothing different happening there compared to simple Deceleration), you can freely change back to Accelerating in the next Phase because you are doing so by simple sail trimming that can be done "on the fly". However, if you start to reduce speed by Let Fly you have made a drastic change to your sails that cannot be undone until you have come to a complete stop, and then it takes a full Phase to retrim things before you can get underway again.
Does this sound correct?
As a P.S. another thing that confuses me about Deceleration vs Backing Sail is that Backing Sail cannot be done if the wind is aft or abeam. Ok, fine. However, the generic Deceleration rule has no such restriction so then why even bother with the notion of Backing Sail and just use the generic Deceleration rule to get the wanted effect? Or is the intention that because of the way square-riggers work they cannot reduce speed at all (Except by Let Fly perhaps?) if the wind is aft or abeam because the only way they reduce speed is by Backing Sail? Very confused here as to how to apply the game rules as they are written.