With Caughey now a spectator, Coley had a mathematical chance at the title and was second fastest qualifier with a 39.917s best lap, behind Auckland's Baden Gray and ahead of then 3NZ Nick Berryman of Rotorua.
In the end, Berryman would go on to win the round and leapfrog Coley to finish as the season's runnerup as he posted another sub-40 second lap in the Top 3 final, after Coley had spun out during the Top 5 eliminator.
Gray finished second and Tauranga's Aaron Hansen was able to climb through the ranks to come third.
Berryman reduced Caughey's title-winning margin to nine points and pipped Coley by two points.
Whanganui's Richard Murray finished fourth after missing out on the Top 3, and was also fourth overall for the Superboats season – a personal best in this division.
Coley's end-game for most of the season has been finding the right package for Poison Ivy to have a crack at the UIM World Series in Australia this year, the same as Murray and Travers, with Travers finishing fifth on the day in Waitara.
Having put in a new cam shaft, Travers was delighted with the added power in the boat, but still needs to get the jet unit properly tuned in to harness the power ahead of the series, which will be held near Adelaide on October 27-28 and near Brisbane on November 3-4.
"We've got some computer stuff to go in, so I can go on to read the exhaust temperature, which I've never been able to do before," he said.
"We're definitely on the right track and I'm more than happy."
In Waitara, Travers was about two tenths of a second off qualifying for the Top 3 final.
"In the Top 9 I put a bigger nozzle in, which was the wrong way to go. It slipped," he said.
"Went back to the original in the Top 6.
"It was just a major sun strike – I couldn't see the water, nothing, the bank, nothing. I had to button off."
Travers was always likely to finish with 3NZ, improving on his fourth place last year, as Hamilton's defending champion Ollie Silverton and Christchurch's rapidly improving Simon Gibbon were neck-and-neck heading into Waitara, separated by just two points.
In the end, Silverton won the day and the title, with Gibbon coming second and the 2NZ in a repeat of the 2016-17 placings, except much closer.
New Plymouth local Neil Marshall was third on the day, while Travers' son Shane was able to finish as 2NZ for the season in the separate Group A Navigator standings – as Whanganui's Donna Thompson served as Gibbon's navigator for only three rounds on a day licence.
In the Group B division, Minnell came into the round on her husband Leighton's track in 3NZ and stayed there as she came seventh on the day in Waitara.
Waikato's Karl Beaver won the round, with the Te Awamutu's defending champion Paddy Haden coming second to comfortably wrap up another title, while Hawke's Bay teenager Jakeb Simmons, still at high school, was able to climb through the ranks for an encouraging third place.
Taranaki's Daniel Reade was fourth on the day to keep 2NZ away from Minnell, while Whanganui's former champion Hayden Wilson was fifth on the day, maintaining his fourth place overall in his return season to the sport.
Final Placings
Superboats: 1. P Caughey 167; 2. N Berryman 158; 3. R Coley 156; 4. R Murray 147; 5. B Gray 138.
Group A: 1. O Silverton 177; 2. S Gibbon 174; 3. R Travers 161; 4. A Ryan 133; 5. S Rice 130.
Group B: 1. P Haden 175; 2. D Reade 162; 3. K Minnell 155; 4. H Wilson 150; 5. J Simmons 147.