A Marine Casualty Investigation Board report into the capsizing of a Galway fishing vessel off Scotland last year has been unable to determine what caused the boat to flood and sink so quickly.
However, the report noted that the crew of the MFV Iúda Naofa - all of whom survived - were not able to start a portable pump landed on to the deck by a British Maritime and Coastguard Agency (MCA) helicopter.
The report also said it was “fortunate” that a sister vessel, the MFV Star of Hope, from Ros-a-Mhíl, Co Galway, was close by at the time of the incident some 80km north of the Hebrides on January 20th, 2015.
The sinking, which was filmed from the helicopter involved in the rescue, occurred in just 35 to 40 seconds from the time the crew gathered on the aft deck.
The two Irish fishing vessels were about to return from a mackerel fishing trip when the forepeak bilge alarm sounded on the Iúda Naofa, water was observed in the bilge and the pumps on board the boat could not stem the flow of water.
A British MCA helicopter from Stornoway responding to the vessel after the alert was raised by the skipper.
The helicopter then lowered a portable pump on to the deck of the vessel, which the crew were unable to operate.
After the pump had been lowered the skipper ordered all crew to don immersion suits and lifejackets as he realised the vessel was in “imminent danger”.
However, two of the crew removed their lifejackets as they found it difficult to work on saving the vessel in them, and one of the crew unzipped his immersion suit for the same reason.
The report noted that the vessel had two liferafts with hydrostatic releases.
It said that the starboard one surfaced - but the port one appeared to have become trapped under the vessel when it floated free.
The crew then mustered on the aft deck as the vessel broached.
Four of the five crew members were washed off by a wave, before the vessel sank.
The report said that the “final deterioration was sudden, with the vessel sinking in less than a minute”.
Two of the crew reached the liferaft and were taken on board the MFV Star of Hope and three were winched on board the helicopter and taken to hospital in Stornoway.
None of the five crew required medical treatment afterwards.
The report noted that the 37-year-old vessel was subject to regular surveys and maintenance.
The boat had been surveyed in September 2014, when two planks were replaced.
However, the report said: “The possibility of hidden weaknesses cannot be ruled out.”
Neither skipper Mairtín Ó Conghaíle nor his crew remembered any impact in the bow area.
The report said the vessel was only travelling at four to five knots, so speed was not a factor in the incident.
The report said that without physical evidence from the vessel, it is not possible to determine how it sank.
It recommended that portable pumps have “clear instructions” attached to them, and a marine safety notice should be issued informing the industry of this.
It also recommended that hi-line protocols be included in safety training for fishing vessels, as only one of the five crew had adequate training in working helicopter hi-lines.
Mr Ó Conghaíle also recommended that the gloves on survival suits be re-designed for greater dexterity in situations where crew are trying to use equipment to save a sinking vessel.
The sinking was captured in a documentary, Snámh in Aghaidh Easa (Swimming Against the Current), which was made by Mr O Conghaíle's son, Mairtin, and broadcast on TG4 late last year.