The grounding of a tourist catamaran on a well-charted reef occurred while the skipper was working alone in the wheelhouse and focused on giving a commentary and staying close to a pod of dolphins, a report has found.

A report by the Transport Accident Investigation Commission into the October 2018 grounding said the Fullers GreatSights vessel Dolphin Seeker had six crew and 47 passengers on board when the skipper located a pod of dolphins near Brampton Reef, not far from the Waitangi Treaty Grounds.

The skipper was manoeuvring the Dolphin Seeker to stay with the pod when the vessel ran aground on rocks at low speed.

No one was injured but the vessel sustained serious damage to both propellers and minor damage to its hull. The passengers were transferred to another vessel and the Dolphin Seeker was re-floated on the rising tide and towed back to its berth.

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The commission found the grounding occurred because the skipper was focused on giving a commentary over the public address system and staying close to the dolphins so didn't notice the vessel had moved into shallow water.

The commission also found the skipper was effectively working alone in a high-risk situation with few or no defences to prevent the one-person errors that resulted in the grounding.

After the accident, the company took measures to address the gap in its safety management systems.

The key lesson, according to the commission, was to ensure adequate measures were in place to minimise the risk of one-person errors when skippers were operating vessels alone in high-risk situations.

Brampton Reef, also known as Brampton Shoal or Brampton Bank, is the remnants of a lava flow which takes its name from the ship which "discovered" the then-uncharted reef in 1823.

The Brampton had arrived a few weeks earlier with missionaries Henry and Marianne Williams and was on its way back to Sydney when it ran aground.

The 28 passengers on board included the Rev Samuel Marsden. Luggage, provisions and timber were salvaged before the ship broke up days later.