A 20ft Wilson Flyer boat has been taken from its mooring at Fareham Creek.
Police want to hear from anyone with information about the vessel which disappeared over the weekend.
The owner had recently fitted a new £5,000 Tohatsu outboard motor to the boat, which was moored in the centre of Fareham Creek near Trafalgar Yacht Services.
Sgt Jayne Goodyear, of Fareham police, said: "It is likely that the boat was taken at high tide between 1am and 3am, as this is when it would have been easiest to move it from its moorings.
"It is a very distinctive boat in that it is bright orange and blue, so I am sure that anyone who saw it on the water around the time it was taken would remember it.
"I would ask anyone who saw anything suspicious, or anyone who has been offered for sale a boat or outboard matching this description, to contact us."
Anyone with any information should contact police in Fareham on 0845 045 4545 or Crimestoppers anonymously on 0800 555 111.
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