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2. If the intended manoeuvre is likely or certain to oblige other vessels to change their course or speed, vessels except ferry-boats carrying out any of the manoeuvres referred to in paragraph 1 above shall announce the manoeuvre by sounding in good time:

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• Three long blasts followed by one short blast when, to enter or after leaving, they have to turn to starboard;

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• Three long blasts followed by two short blasts when, to enter or after leaving, they have to turn to port;

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• Three long blasts when, after leaving, they wish to cross the waterway.

Before completing the crossing, they shall, if necessary, sound:

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• One long blast followed by one short blast if they wish to turn to starboard, or

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• One long blast followed by two short blasts if they wish to turn to port.

3. The other vessels shall change their course and speed if necessary.

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