Seaman Like Rounding - The definition of Mark-Room and the definition of "Proper Course" take care of this.
A non Right of Way boat entitled to Mark-Room can only sail to the Mark and then her proper course around the mark. The course she sails around the mark might look like a tactical rounding to block another boat, but she must be allowed enough room, while at the mark, to clear the mark in the conditions present at the time. Since the new RRS do not use the term "Seaman like Rounding" The term Mark-Room and Proper course definitions take care of this. To apply these 2 definitions to a boat at a mark rounding, the Keep Clear boat entitled to Mark-Room must be provided room to sail "to the Mark". This does not allow the boat to sail wide, as that is not "to the mark". Once the boat is at the Mark, her entitlement is only to sail her Proper course around the mark. It does not provide extra room to sail wide to the mark while approaching the mark. It also does not require the boat entitled to Mark-Room to sail her Proper Course while at the mark, but if she does not, Section A rules still apply.
Here are a couple of Cases that are good examples of Mark-Room and “sailing to the mark”, and sailing your “proper course while at the mark”
http://game.finckh.net/reg_gbr/cases/case70.htmhttp://game.finckh.net/reg_gbr/cases/case21.htmRoom
The space a boat needs in the existing conditions while maneuvering promptly in a seaman-like way.
Proper Course
A course a boat would sail to finish as soon as possible in the absence of the other boats referred to in the rule using the term. A boat has no proper course before her starting signal.
Mark-Room
Room for a boat to sail to the mark, and then room to sail her proper course while at the mark. However, mark-room does not include room to tack unless the boat is overlapped to windward and on the inside of the boat required to give mark-room.Tactical Rounding - When the boat has the Right of Way and does not have any limitations from Section B or C of Part 2 Rules, she may make a tactical rounding.