All three occupants suffered scratches and bruises, with one trapped under the overturned vessel for a short time and suffering further injuries.
The three occupants were rescued by another boat that was in the area at the time.
Judge Dawson said that the defendants' behaviour put them both, as well as their passenger, at risk.
"I suspect I don't need to tell you what a stupid thing it was that you did and the risk you ran," he told the pair.
He also referred to recent boating tragedies and implored the defendants to be more careful in the future before fining them each $1500.
Council regional compliance manager Patrick Lynch said it was a "serious and completely avoidable incident".
"Quite simply, these people could have died and we need all boaties to learn from this," he said.
"Such incidents show how real the risk of a bar crossing is and we hope it's taken as a warning to be prepared and well equipped beforehand.
"Just as importantly, people should be prepared to change their plans and not attempt the crossing if unsafe to do so. The fish will be there another day."
Lynch said the convictions and fines paled against the tragedy that could have occurred.
The sentencing follows a growing list of tragic water incidents this summer, and a couple of "lucky escapes" in the Waikato region.
In the first incident on December 28, three people ended up in the water while crossing the Raglan bar. They were rescued by a jet skier in the area.
Less than a week later, on January 3, two people were thrown into the water at Tairua on the Coromandel Peninsula's east coast. They were picked up by a surf life-saving club rescue boat.
The following day at Matarangi, further up the peninsula's east coast, three boats got into difficulty after losing power coming back in over the bar.
A regional council maritime boat responded and co-ordinated the initial rescue, which involved the use of jet skis to recover six people from the water. Maritime officers later towed another vessel back to harbour.
A fifth incident occurred the very next day when a boat overturned in the surf off Pauanui beach while attempting to assist two kayakers, resulting in a fatality.
Council regional harbourmaster Chris Bredenbeck said: "It's the riskiest activity you can carry out on the water and it's a real worry to have had these separate bar crossing incidents on both our coasts."
Bredenbeck said weather, current, and tide conditions caused waves to break in an unpredictable pattern on bars, creating an unstable and hazardous environment.
Sand bars were common around the country in harbours and rivers. To get out into open sea they usually have to be navigated, and they can be extremely dangerous, even for experienced boaties, the council said.
Those planning to undertake a bar crossing should:
• Thoroughly check marine weather and pay close attention to the swells;
• Check the tides and avoid crossing a bar at low tide;
• Seek local knowledge before attempting to cross a bar;
• Secure loose gear and ensure everyone is wearing a securely fitted lifejacket;
• Always take two forms of waterproof communication so help can be sought if needed;
• Spend some time observing the bar before attempting to cross it;
• Contact Coastguard on VHF to let them know your intentions to cross the bar and that you made it across safely.
