Green is right-of-way boat for Red and Blue and therefore obstruction. When Red establish an overlap, right of way changes. Rule 11 requires Blue to keep clear. Rule 15 and because of changing course rule 16.1 requires Red to give Blue room to keep clear. From the time the overlap begins Blue is unable to give Red room to pass safely between Blue and Green. Therefore Red is not entitled to room to pass between Blue and Green (See last part of rule 19.2(b)).