Even its standard return single adult fare of $30 will be $6 cheaper than offered by either Fullers or Explore, although a $20 children's ticket will cost $2 more.
Explore chief William Goodfellow yesterday acknowledged Sealink's arrival had taken him by surprise, but said it had not stopped his new service from gaining strong customer support.
"We are here for the long term, providing a full service into the future," he told the Weekend Herald.
But his counterpart at Fullers, Doug Hudson, said it was disappointing Sealink had decided to "cherry-pick" the weekend summer market.
"That takes the cream off it for other operations which are there for all year round, and that's the disappointing part," he said.
Sealink managing director Todd Bolton said his company was simply making the best use at weekends of three vessels it had bought for a five-day commuter service it took over in August between Pine Harbour and Auckland, and wanted to "grow" the market.
"We were probably looking well before Explore at opportunities for engaging those vessels on other routes," he said.
"It's a very competitive market now, but also a big growth market with tourism, so we think we can provide a unique service a little different to the others."
Long-time Waiheke resident John Stansfield said he was "thrilled to bits" to see more options than Fullers previously offered as a lone operator.
"It's great to see boats at different times and lovely not to have to stand in a queue that goes from the ferry to Khazakhstan on a Friday."