"There's a huge amount of stolen boats out there being bought and sold by innocent people," he said.
A nine-point second hand boat-buying checklist on the police.govt.nz website suggested potential buyers check serial numbers of boats and engines, registrations of trailers, and boat ownership histories. It also suggested confirming the details of sellers by meeting them at their homes.
Bay of Plenty regional harbourmaster Peter Buell said he received occasional reports of boats being stolen, and these were passed on to staff undertaking four daily patrols in the area.
Anecdotally, there seemed to be a growing number of thefts from boats in the Bay. Missing items included oars, life jackets, lines and dinghies.
"It's quite shocking," he said. "When people are stealing life jackets, that's an important piece of safety gear that has to be replaced immediately."
Insurance Council chief executive Tim Grafton said an average of 24 boats were being stolen throughout New Zealand each month, and there had been a rise in the number of trailered boats being stolen from yards and driveways over summer.
Mr Grafton suggested owners secretly mark their boats to help identify them.
"Thieves will often disguise a stolen boat by repainting, renaming it and swapping trailers and motors," Mr Grafton said. "So hidden unique identifiers are important - for example a splash of paint under the seats."
The council recommended owners park their trailered boats where they could not be seen from the road, chain trailers to solid objects, clamp trailer wheels, lock outboard motors, remove auxiliary motors from boats, and record serial numbers.
Mr Grafton said the size of an outboard motor was little deterrent to thieves, who often stole even the heaviest ones.
Bay boat thefts
Jan 3: Dinghy, Papamoa Beach
Jan 1: Catamaran, Omokoroa
Nov 21: Malibu kayak, Mount Maunganui
Sept 6: Frewza F18 boat (5.7m), motor (115hp), trailer, Waihi Beach
Sept 5: Huntsman Dorado boat (5.5m), motor (115hp), Bowentown