Minnell struggled in Waitara, likely because of his non-stop work preparing the debut event for the track he had built, and then also at Hastings, but his top 3 placings in Meremere and twice at Whanganui left him just a point behind Head.
Coley's spectacular crash at Whanganui in December brought national headlines, but it was the 10th at Waitara due to engine problems that really looked like costing him following a series of third placings.
Murray's best effort was second at Hastings, while he hovered around the top 5 in the other events despite several near-misses and spills.
So it all came down to Featherston on Sunday and when Head (engine), Murray (wrong turn) and Minnell (slow time) all dropped out in the top 8, it was left to Caughey and Coley to decide the title, with the Christchurch racer claiming his fourth round victory and another championship.
Minnell's wife Kellie, who started as navigator for Coley but switched back to her husband's boat after the December crash, would finish second in the separate navigator's championship behind Caughey's teammate Shama Putaranui.
Defending Group B champion Ross Travers would eventually return to the form which saw him dominate the previous season, but he had given too much of a head start to the incredibly consistent Paddy Haden, as the Te Awamutu driver won Meremere and Whanganui in December, then finished second to Travers at each of the remaining four rounds.
Travers needed Haden to have some kind of issues like he himself experienced at Whanganui in December when finishing sixth, but it never happened.
Fellow Whanganui driver Hayden Wilson was also on the outside looking in as he struggled around the bottom of the top 5 until the boat came right at Hastings with a third placing, and then the Whanganui night round as runner-up.
However, that placing was taken away from him post race, due to a timer error by the officials for fixing his boat, meaning Owanga's Tim Edhouse remained in third position after a season of second to third placings - only missing the series runner-up spot when Travers made his late run.
In the same spot as their drivers, Whanganui navigators Shane Travers and Chris Hausman came second and fourth respectively.
The other Group B Whanganui driver was Donna Thomson, who finished in the middle of the 12 boat points table with a best result of fourth in Whanganui in December, but stayed in the fifth to seventh bubble for the remainder of the campaign.
Next season, Whanganui should be represented in all three divisions for the first time since 2014.
In another thrilling chase, Sam Newdick, with four round wins, had to come from behind to overtake Gisborne's Blake Briant (two wins, three runner-up), with Briant's sixth placing at the Whanganui night round ultimately costing him the title in the 11-boat division.