Section C rules do not apply at a starting mark surrounded by navigable water or at its anchor line from the time boats are approaching them to start until they have passed them. When rule 20 applies, rules 18 and 19 do not.
20.3 When Not to Hail
A boat shall not hail unless safety requires her to make a substantial course change to avoid the obstruction. Also, she shall not hail if the obstruction is a mark that the hailed boat is fetching.