According to local press, a Lowestoft fisherman had taken his 9m vessel to sea with his stepson and the diver aboard.
After an early departure, the boat sank at around 8.30am today in conditions described by the Maritime and Coastguard Agency as moderate to rough, with a 2.5m swell and a southerly Force 4 wind.
Before sinking, the boat reported to Yarmouth Coastguard that it had lost power in a position 12 miles off Happisburgh.
The Happisburgh RNLI B Class Lifeboat was sent to assist, while the Caister independent lifeboat was launched in case further capacity was required.
Once the fishing boat had gone down, the Caister lifeboat was able to step in as the main rescuing vessel and, upon arrival at the site, found the three crew in the water.
The diver was suited and the stepson had a lifejacket, while the skipper was swimming unaided.
They were taken into Yarmouth and transferred by ambulance to James Paget University Hospital at Gorleston for treatment for “shock and cold”.