Not 18.4, RRS 10.

Not RRS 10 (yet).

No contact.

No avoiding action by Red.

Yea I guess so ... would be nice to see Red wiggle. 

Of course, it is a theoretical case that we discussed with my students.
Let's see now with the new position 4.
For me in this case, blue doesn't break any rules.

What do you think ?
THANKS !!!

As John A rightly points out (assuming these boats are not on a plane or otherwise moving at high speeds), given the boats are separated by 1 boat-width, Red needs to alter course toward Blue to initiate a potential rule-breach.

For Blue to be breaking RRS 10 at #4, Red would need to claim [show] that Blue was not keeping clear .. and that would require the conclusion that immediate contact would have occurred between the boats had Red altered course toward Blue.

For me in this case, blue doesn't break any rules.

Agree. Blue (on port tack) is not a right-of-way boat. Therefore 18.4 does not apply.