The first thing we notice is that a mark must be designated as such in the written sailing instructions. According to rule J2.1, the SIs must include a description of all the marks; therefore, anything not mentioned in the SIs is not a mark.

What makes an object a mark is the requirement (by the SIs) that boats must leave it on a specified side. All marks are objects that must be passed on one particular side during the course of a race. If it doesn't matter which way you pass an object, it's not a mark.

The most familiar marks are the buoys used to designate a race course, such as the windward, leeward and jibe marks. These are considered rounding marks because boats must round them in order to sail the course properly.

Other objects can also be marks. The ends of the starting and finishing lines are marks because the SIs say you must leave them on a specific side when you are starting and finishing. Also,

if the sailing instructions say that all government aids to navigation must be regarded, then these are considered marks because they have a required side (even though you don't have to round them).

The last sentence of the definition describes two things that are not considered part of a mark. The first one is the mark's anchorline. This line is sometimes considered an obstruction (see below), but it does not rank as part of the mark itself. For this reason you won't be penalized if you touch the anchor-line (as long as you don't touch the floating mark).

The second thing that is not part of a mark is any object that is attached temporarily or accidentally to it. For example, a tree branch accidentally caught on the leeward mark may be an obstruction, but it's not considered part of the mark. Similarly, a small boat tied to the stern of the race committee boat for a few minutes is not considered part of that mark at the start or finish. And a standoff buoy temporarily tied off the stern of the committee boat has the same status unless the SIs say otherwise. A mark is any object that is defined as such by the sailing instructions. The most common marks are usually yellow

or orange and filled with air, but almost anything can be a mark. This includes the ends of the start and finish lines, all the rounding marks and any government buoys that must be regarded. However, the anchorline attached to a mark is not considered a part of it.

Definition: Mark

An object the sailing instructions require a boat to leave on a specified side, and a race committee boat surrounded by navigable water from which the starting or finishing line extends. An anchor line and objects attached temporarily or accidentally to a mark are not part of it.

Watch out for obstructions!

T3 ule 18 applies not only at marks, but at obstructions too. So it's important to know fvhow the rulebook defines an obstruction.

An obstruction is, essentially, an object that's large enough to require a boat to change her course significantly to avoid it. The definition says specifically that an object is an obstruction only if it requires a boat to make a substantial change of course when she is steering directly at it and one boat length away. (Note that a racing boat doesn't have to be aiming at an object in order for it to be 'an obstruction).

Common obstructions include the shoreline, a breakwater, moored boats, rocks, ships and other big or dangerous things that get in the way of racing boats. Pot buoys, moorings, stakes and other smaller objects are