Maritime New Zealand is urging boaties to take care after a crash sent a 13-year-old boy tumbling overboard in Auckland.
The agency said the incident served as a timely warning for how quickly a boating trip could turn "disastrous".
The man will be required to pay nearly $25,000 in fines and reparations after he collided with a sailing boat carrying 10 passengers.
Jae-Ho Huh was sentenced in the Auckland District Court on Friday, after his 11-metre launch collided with the SV Arcturus in March 2020.
Huh's boat was travelling under auto-pilot, and caused a collision that Maritime New Zealand said was entirely avoidable.
The crash sent the teenager overboard and caused two other passengers, one aged 12, to jump in the water for fear of injury.
Though the boys were retrieved immediately, the second person, an older man, drifted farther away. Huh attempted to rescue the man, but almost ran him over - he then collided with the SV Arcturus a second time.
Passengers on the SV Arcturus said they yelled and waved to the boat, but it did not slow down.
Northern compliance manager Neil Rowarth said the incident could have had tragic consequences.
"I urge everyone who has a boat to know about sailing and the rules of the sea," he said.
"Join a boat club, take Coastguard boating education lessons and keep safe."
Huh has been fined $3900 and ordered to pay $18,538 in reparations for consequential loss alongside $500 for each victim.