Five people whose small boat sank in Wellington harbour would likely have died if not for their life jackets, police say.

The group were on board the small run-about “Hustler” when it sank between Matiu/Somes Island and the Seaview Wharf about 7pm on Sunday.

“We got the call once one of the survivors had swum to shore but the communications were fairly scratchy, possibly due to a wet phone being used,” said Wellington Police Maritime Unit Sergeant Richard Kennedy.

 “The light was fading due to the hour of the day, and we had Search and Rescue (SAR) on standby just in case.

 “The fact that they were all wearing life jackets, has saved their lives.”

At least one of the five was not a strong or confident swimmer, so the lifejacket would have been the difference between life and death, he said.

Three of the group suffered from hypothermia due to their lengthy spell in the water.

Skipper Kerry McIvor was glad they were all wearing their life jackets.

 “We had the life jackets and we had our mobile phones to call for help if we needed to,” McIvor said.

“We had anchored between Matiu/Somes Island and Petone and were fishing when we started taking on water.

“We had a bilge pump but it couldn’t cope with the amount of water.

“We pulled the anchor up and began motoring back to Seaview but the water coming on board was too great - the stern went under and the boat sank a few hundred metres off Seaview Wharf and all of us ended up in the water.”

McIvor and his friend swam about a kilometre to shore, climbed onto the Seaview Wharf, and raised the alarm.

The boat was discovered by a commercial fisherman the next morning, partially submerged. Photo / Supplied

“My mate held his mobile phone above his head the whole way.”

Sergeant Kennedy said if the group had their communication devices in dry, waterproof bags they might have been able to call for help earlier.

“Once your comms are wet, they are almost impossible to use,” he said.

“While a Marine VHF radio or a beacon (Emergency Positioning Radio Beacon – EPIRB) are not always accessible to everyone, they too can be lifesaving pieces of boat safety equipment.

“These were not on this vessel either.”

The three remaining boaties were stuck in the water waiting for help for close to an hour.

They were rescued by Police RHIB Hukatai and taken to hospital for treatment for hypothermia, but “Hustler” was nowhere to be found.

It was thought that Hustler had sunk, but a skipper from a commercial fishing boat exiting Wellington Harbour on Monday morning noticed a partially submerged boat drifting out in the shipping lane at the harbour entrance.

The skipper contacted authorities and the Police Maritime Unit removed the hazard which turned out to be the missing vessel.