A dirty hull may well be the reason why a French-registered cable-laying ship named Ile de Re has been circling off the Bay of Plenty coast over the last couple of days.

The Marine Traffic website shows the ship made a rendevous with the Tauranga-based Western Work Boats vessel Tranquil Image.

The French cable ship Ile de Re. Photo: File.

However, the vessel's owner, Sean Kelly, says he is 'not at liberty to discuss” why his boat met up with the European ship.

He referred inquiries to the Minister of Primary Industries, which states its role to date has been to ensure the vessel is free from any bio-security risks, and in this case bio-fouling.

'MPI believe the vessel is affected by bio-fouling,” says an MPI spokesperson.

'To mitigate any bio-security risk, MPI instructed the vessel to remain off shore and undergo treatment before coming closer to New Zealand.”

The hull scraping is expected to be completed in three-to-six days. MPI will permit the vessel to land in New Zealand once it has evidence that the treatment has been carried out correctly.

At the time of writing, the Ile de Re has not declared the purpose of its visit to MPI.

The vessel's track on the Marine Traffic website shows the ship has been cruising between Mayor Island and the Rangitira knoll, over water of up to 700m deep.

A Tauranga observor says the Marine Traffic track showed the Ile de Re came down to Auckland from its base at Nouméa, New Caledonia two or three days ago.

Marine Traffic's record of the ship's track.

It went right down the Rangitoto channel without callling at the port. It did a couple of sweeps around the top of the Hauraki Gulf then steamed straight down to the spot in the middle of the holding pattern.

The Marine Traffic track shows the ship also met with Tranquil Image on Sunday night.

The Ile de Re is a 143mt long cable ship capable of loading up to 6,000 km of cables and providing state-of the art equipment for cable laying and maintenance.

It is owned and operated by Alcatel-Lucent via ALDA Marine, in a joint venture with Louis Dreyfus Armateurs (LDA), who manages the ship. There is a crew of around 25 on board.

Ile De Re has recently been involved in linking Tonga to the Southern Cross Cable – the main trans-Pacific system that connects Fiji, Australia and New Zealand to the United States of America.

The connection between Tonga and Fiji is part of the regional connectivity project which is aimed at connecting all Pacific Islands through fibre optic cable.

The project is financed partially by World Bank, the Asian Development Bank and Tonga Communications Corporation.

The Ile de Re is under charter to the South Pacific Maintenance group to provide cable services throughout the South Pacific and provides coverage for Australia/Japan cable to Guam.

A graphic showing the rendevous with Tranquil Image.