Ports of Auckland says that on Monday this week it had to pay 26 wharfies almost $5500 for unworked downtime after they finished loading a ship about three hours into their eight-hour shift.
It says that is just one example of why its three-shift daily rostering regime stops it from lifting a labour "utilisation" rate of 65 per cent to more than 80 per cent, as achieved by the Port of Tauranga.
The argument over working hours is at the heart of the six-week dispute, which remains unresolved after mediation failed again this week.
The Maritime Union tabled a new offer on Thursday, to extend shifts by extra hours if needed to send a ship on its way in return for some form of penal rates no longer paid at the port.
But it was dismissed by the Ports of Auckland, which wants to introduce a roster similar to that used at ports such as Tauranga.
Tauranga has 12-hour shifts for most stevedores but six-hour stints for higher-skilled crane drivers. Tauranga workers start and finish according to ship movements, and have four days off after four working days.
Ports of Auckland is pressing for far greater fluidity, involving shifts varying from five to 12 hours.
That would be in return for a 10 per cent increase in hourly wages, which for standard duties such as driving container straddle carriers are $27.26 an hour and rise to $32.96 for specialist tasks such as operating 700-tonne cranes.
The company says wharfies would be able to book shifts four weeks ahead to plan a better "work-life balance", although it could still make changes until 24 hours beforehand to cope with unforeseen shipping delays.
Fulltime permanent employees would be guaranteed 160 hours a month rather than their existing 40 hours a week, stoking union fears of wild oscillations in working patterns.
One veteran wharfie, who asked not to be named because of a dispute he faces with the company, told the Weekend Herald it was already difficult juggling work and family commitments while getting just one weekend off in every three.
Shifts varied between day and night and the wharfies got to choose only one of their two days off, on weeks with working weekends.
The man's duties vary from driving container straddles to and from ships to operating the giant cargo cranes, alternating with duties as a deck foreman, using a hand-held radio to guide loads "under the hook".
To keep cranes operating continuously, two alternating drivers and a foreman are assigned to each for an eight-hour shift.
Drivers take turns filling in for the foreman during that person's breaks.
The first driver spends 3.5 hours a shift operating the crane, and an hour and a half acting as foreman, leaving the other to complete the other 4.5 hours of cargo-loading, alternating with an hour on deck duties.
That leaves the first driver with up to three hours of breaks a shift, and the second with 2.5 hours in the mess room, although the wharfie said they often had to perform other duties in what the company counted as downtime.
Although the company says the first driver is often sent home for the final two hours of a shift, the man noted it was always at the employer's discretion, and insisted he and his colleagues gave good service for what he acknowledged were ample wages.
"I know people think we are so lazy we sit down with our fingers up our arse all the time but you could be carrying up to 80 tonnes of load and if you make a mistake and there's men around, there's no second chance, so it's high concentration," he said.
"It's all about being efficient and doing it properly."