"They are not that much bigger than the ship carrying 600,000 barrels- the difference is that we are proposing that they come in with the bigger load of crude on board, which means they will sit lower in the water.
"By our reckoning, the ability to bring in bigger parcels of crude is likely to add US.20 to US.50 (24c to 60c) a barrel, either as margin for our customers, or margin for the refinery [this is yet to be decided]," Mr McNeill said.
"Either way, the proposal would make the refinery more competitive, and thence attractive for our customers to continue making make fuel product in New Zealand."
He said the refinery had a special relationship with local hapu Patuharakeke and three hui had been held to date with hapu and iwi on the harbour.
He said the proposal to dredge was one of several initiatives to improve the refinery's competitiveness in an ultra-competitive Asia-Pacific refining sector, and to grow revenue. Refining NZ made a net loss of $6.9million for the June half-year, a reversal from the $5.2m profit it made in the corresponding period last year.
Juliane Chetham, a trustee of the Patuharakeke Trust Board, said her people needed to understand the full impacts of the refinery's plan as it felt the harbour was already in a degraded state because of pollution and harvesting issues.
Since the hapu and refinery signed a memorandum of understanding more than 10 years ago, she said both had had discussions on various resource consent matters but the latest proposal was a major development that needed to be worked through carefully.
"We may end up opposing it. The onus is on them to prove that this is sustainable but the good thing is they are engaging with us at an early stage and we're able to see their technical reports as they come through," she said. Ms Chetham said Patuharakeke, in partnership with other hapu, would undertake a cultural impact study of the proposal to dredge the harbour.
"We don't deny the important contribution the refinery is making to the local economy but environment protection is the bottom line for us.
"Already the pipi beds are closed because they've been so depleted and we're concerned about the scallops as well," she said.