Port of Tauranga's container volumes this year are shaping up to be a bit of a riddle.
New Zealand's busiest and biggest port has had to handle a wave of unscheduled container ship calls diverted from Auckland since October due to that import port's productivity and congestion issues.
The Bay of Plenty port last month had more than 20,000 boxes stacked up in its yard - many diverted cargo destined for Auckland.
But chief executive Mark Cairns is expecting container volumes to be down on last year.
"We have had 11 unscheduled container vessel calls that diverted from Auckland due to their congestion issues.
"However with the flow-on berthing congestion, with vessels being off-window, we have handled 67 ships less than last year at Port of Tauranga."
Off window means ships berthing outside fixed and scheduled times.
Missed windows are happening around the world amid global shipping congestion and soaring consumer demand for imports post-pandemic outbreak. The result in New Zealand has been supply chain congestion, exacerbated by lengthy delays for visiting container ships to tie up and unload at Auckland.
Another factor complicates the container volume arithmetic at Tauranga, Cairns said.
"As a result of the congestion in Auckland since September, the average container exchange per vessel has been up around 20 per cent. So counter-intuitively, the outcome of all this is that we are expecting container volumes to be down on last year."
Average container exchange is the average number of container moves on a vessel – imports and empty containers off the vessel and exports and any empty export boxes on to the vessel.
"So in addition to the 11 additional vessels we had bypass Auckland, we had customers utilising existing Tauranga services by an additional 20 per cent more than normal, " said Cairns.
Tauranga port's container terminal area was now "in really good shape" after the height of container congestion saw more than 20,000 boxes in the yards.
Many were import containers awaiting rail transport to Auckland after being diverted to Tauranga.
Cairns said on Monday 16,000 containers were in the yard, only 1500 of which had to be railed to the port's inland hub Metroport in Auckland.
"We are pleased to finally be back running 90 trains per week (between the port and Auckland) which is what we were running two years ago."
On Monday night only one container ship was waiting at anchor to berth.
In separate advice to customers, the port said the backlog of import containers destined for Metroport had cleared and delivery timeframes had returned to normal.
"From early April the team at KiwiRail have been able to assist us with additional capacity and we have been steadily reducing the import backlog ever since."
Normal average delivery timeframes to Metroport after wharf discharge were less than two days for priority managed cargo and three to four days for standard cargo.