Obstruction   An obstruction is

(a) an object that a boat could not pass without changing course

substantially, if she were sailing directly towards it and one of her hull

lengths from it;

(b) an object that is so designated in a rule;

(c) an object that can be safely passed on only one side; or

(d) an area or line in a rule that boats are prohibited from entering or

crossing.

However, a boat racing is not an obstruction to other boats unless they are

required to keep clear of her or, if rule 22 applies, avoid her. A vessel under

way, including a boat racing, is never a continuing obstruction.