Q.What is the difference between abort point and point of no return?

Abort point is the point on the passage beyond which there is no sufficient sea room to turn back the vessel. When approaching or entering a port or procedding in a channel, the width of the channel may not be sufficent to turn the vessel. 

The point where width of the channel becomes narrow enough that vessel cannot make a turn would be called Abort point.

Point of no return is not related to the width of the channel or turning of the vessel. With "point of no return, there may be sufficient sea room to turn the vessel but the vessel cannot return to where it came from because the conditions have now changed.

One example of "point of no return" is while proceeding in a river with falling tide. If the next port is changed or cancelled after passing the "point of no return" then vessel cannot return back because the tide now will be less than it was few hours earlier when vessel passed the same location.

In this case vessel can turn and there is no issue with the turning back and may be anchoring. So it will not be called "Abort point" but it will be called "point of no return".

For more detailed explaination read this blog.

What is Abort Point and How You Can Use it For Safe Navigation