Two boys and their father were rescued in the Thames Estuary on Saturday night after their yacht ran aground.
The alarm was raised by the younger boy, whose father and 13-year-old brother are both profoundly deaf.
Thames Coastguard used VHF direction-finding equipment to get a bearing on the signal, and requested the launch of the Walton Lifeboat and a rescue helicopter from Kinloss.
The helicopter quickly found the yacht and illuminated the area to help the lifeboat crew find it and fix a tow.
Mick Carpenter, Watch Manager at Thames Coastguard said 'This yacht was on passage from Wivenhoe to the Greenwich yacht club when they ran aground in the dark. I would like to praise the young lad who raised the alarm on behalf of his father and brother.'
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