Two 'best friends' died due to carbon monoxide from a leaking heater exhaust as they slept on a boat following a night out, an inquest has heard.
Ronnie Holmes, 60, and Stephen Jewitt, 63, were found dead on Mr Holmes's 30ft (9m) motor cruiser Diversion which was moored on the River Ouse, in the centre of York, in December 2019.
There was no carbon monoxide alarm fitted on the Diversion, which Mr Holmes had built himself over a number of years, an inquest in Northallerton, North Yorkshire, heard on Thursday.
York coroner Jon Heath heard how carbon monoxide alarms became mandatory in April 2019 but Diversion's last safety inspection was two months earlier, in February.
Mr Heath heard how the duo, who were retired power station engineers and best friends for 20 years, met a third man, Christopher Hunter, at the marina at Naburn Lock, south of York, and travelled four miles up the River Ouse before mooring near the city's Museum Gardens.
The three men enjoyed one of their regular nights in a number of York's pubs, before Mr Holmes and Mr Jewitt went back to the Diversion to sleep.
In a statement, Mr Hunter said he left his friends "in good humour" with "no issues or concerns".
The two men were found unresponsive by a police officer when family members raised the alarm the next day, the hearing heard.
An investigation by the Marine Accident Investigation Branch (MAIB) concluded that carbon monoxide had accumulated in the main cabin from a diesel heater which Mr Holmes had bought on eBay.
Rob Loder, from the MAIB, said the exhaust of the heater was found to be leaking once lagging was removed by the investigator. The exhaust pipe also had a silencer fitted which was not suitable for a marine setting, he said.
The inquest heard how Mr Holmes built the vessel over 11 years, starting in 1989.
Mr Loder said the boat was generally very well built.
Raymond Howe, who was the boatyard manager at the marina at Naburn, explained to the inquest how he was an examiner for the Boat Safety Scheme (BSS), and passed the Diversion in February 2019.
Mr Howe said that examiners are not allowed to run or dismantle equipment as part of their inspections and everything seemed in order from his visual survey.
Mr Heath recorded a conclusion of accidental death in relation to both Mr Holmes, of Castleford, West Yorkshire, and Mr Jewitt, of Goole, East Yorkshire.
The MAIB report into the fatal incident detailed a number of deaths from carbon monoxide poisoning on boats in the last eight years.
In January 2014, two fishermen died from carbon monoxide poisoning on board the scallop dredger Eshcol, in Whitby harbour, in North Yorkshire.
A butane-fuelled cooker grill had been left on to warm the boat's cabin. The vessel's owner was jailed after he was charged in relation to the incident.