Brian Owen Daley, 56, of Mowbray, and Gregory John Burling, 58, of Newnham, were found dead on board the Double B at the Gepp Parade Marina in Hobarts north in January, 2016.

Both men died from carbon monoxide poisoning after inhaling generator fumes in their sleep.

The pair had been holidaying on the boat with Barry Lowe and his young daughter.

Mr Lowe owned the vessel along with Mr Burling.

But Mr Lowe and his daughter left the boat the day before the tragedy unfolded, after the young girl started having seizures and had to be airlifted to hospital.

She was later found to have high levels of carbon monoxide in her blood.

Mr Lowe returned the next morning and found the men who had died overnight.

After emergency services arrived, a paramedic reported feeling lightheaded after being in the cabin of the boat.

Releasing his findings on Thursday, Coroner Simon Cooper said the boat on which the men died did not have a carbon monoxide detector.

The muffler of the generator had a fabricated galvanised water pipe elbow attached with a plastic spiral type pipe. It was intended that this pipe was to have been held firm by a lightweight hat hose clamp however the hose clamp was not fit for this purpose, he said.

The muffler was severely obstructed on the end by the fact that a shower fitting was placed on it. This appears to have created a large amount of backpressure in the exhaust system forcing exhaust gases to be expelled, and in this instance from the machinery space area into the cabin.

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Finally, a hole was identified in the plastic piping part of the home constructed exhaust extension system. This allowed exhaust gases to escape directly into the machinery space under the cabin and from there enter the cabin.

As part of his findings, Mr Cooper recommended all boats with enclosed cabins and petrol driven motors should be fitted with a carbon monoxide detector.

He also recommended all petrol driven generators only be used in accordance with manufacturers recommendations, and in particular, not be installed in a confined space and not have the exhaust system modified in any way.

It should be apparent from the substantive finding above that both deaths were entirely avoidable due, as they were, to a poorly installed and maintained petrol driven generator and the absence of any device to warn as to the presence of carbon monoxide in the cabin, he said.