From the case book, this is the decision after an appeal from P regarding a port/starboard incident.
" When one boat is required to keep clear of another, the keep clear boat must take action to avoid a collision EARLY enough to ensure the right-of-way boat has no need to take avoiding action, in the prevailing conditions, P failed to observe this principle and therefore did not keep clear."

I typed this in after reading it on P57 RYA 1986/1 of the case book. There are many similar incidents but this one states "early enough" and "prevailing conditions".

Heres the link
http://www.rya.org.uk/NR/rdonlyres/148BE269-E138-41C3-9D3E-966C78687CFA/0/RYACaseBook20052008.pdf

The ISAF case book link isn't working to good but RYA version should be acceptable given the location of the incident.

Darryn
Mozzy
1782