Red shall keep clear (rule 12 or 11) and give Blue mark-room (rule 18.2(b,c) ). When Blue passes head to wind however, she is no longer the right-of-way boat (see last sentence of rule 18.2(c). Now rule 13 applies and Blue must keep clear until she is close-hauled. Thereafter rule 10 applies, and Blue is right-of-way boat again. Blue tacked so close to Red, that Red probably had to change course before Blue's tack was completed, and certainly had no reasonable chance to keep clear after the tack was done. Therefore Blue probably broke rule 13 and definitely infringed rule 15 and will be penalized. See also Case 27.