As the proposal had yet to be developed into a business case, Mr Caulton said it was early days and the trust had only just identified the potential solution to cater for the growing demand.
"We are at the feasibility stage and building a business case.
"It's too early to say exactly how much it will cost but it could cost around $1.5 million," he said.
If the project progressed, the self-funded, not-for-profit charitable trust would not be seeking public funding for the project.
The trust had looked at eight potential sites within the harbour, including sites at Parua Bay and Onerahi, but had set its sights on the space, which was within close proximity to the city centre and marine services.
While the site would require a significant amount of dredging, it was considered ideal as it also offered sheltered waters and boasted great views of the new bridge, while featuring in the new loop walkway.
Mr Caulton said he feared word of mouth in the boating community was spreading the word about Whangarei's occupancy challenges. "With cruising fleet blogs and websites, it's easy for people to hear that Whangarei is full and then decide to just go elsewhere."
He said the 230-berth marina at Marsden Cove had some availability but foreign boaties were looking for berths closer to Whangarei, where marine services were available.
"We have had to turn around 20 boats away this season. We are not keeping up with the local and international demand," he said. There were a number of vessels on standby and the marina could cater for an extra 30-40 boats if it had more space.
The trust proposed using dredged material from the harbour to reclaim land at the site and create the area for parking and buildings.
Northland Regional Council consents/monitoring manager Colin Dall said the trust would have to get a range of consents for the development under the regional coastal plan, including consent for right of occupancy.
