Three men who died when their fishing boat sank were let down by the coastguard, it has been claimed.

Martin Johnstone, Christopher Morrison and skipper Paul Alliston drowned when the Louisa went down in the Outer Hebrides last year.

The fourth crew member, Lachlann Armstrong, from Stornoway, swam to shore and clung to rocks before being rescued by lifeboat.

The Marine Accident Investigation Branch (MAIB) found a series of problems and mistakes contributed to the sinking on April 9.

They included a faulty life raft, exhausted crew, failed life jackets and an almost hour-long delay in the emergency response.

Andy McMillan, brother of 42-year-old Mr Alliston, has criticised the coastguard's handling of the rescue.

"The crew set off the EPIRB [emergency beacon] but the people receiving the signal took nearly an hour to do anything.

"These guys relied on the coastguard but they let them down - that's the long and the short of it."

Lives may have been saved if rescuers had arrived on the scene sooner, the MAIB said.

A satellite detected the first EPIRB alert from the Louisa at 2.32am, followed by another nine minutes later.

A Royal Navy command centre relayed the information - including a rough location for the Louisa - to a coastguard base in England at 2.50am.

They passed the information to a coastguard team on Lewis and asked them to contact the boat. They paged Barra RNLI at 3.22am and requested a search and rescue helicopter five minutes later.

The Barra RNLI lifeboat launched at 3.40am and arrived at 4.13am. A helicopter arrived almost an hour later at 5.10am, having flown 110 miles from Stornoway.

"Every second counted but they waited to confirm the position," Mr McMillan said.

"They get a mayday and they first try to phone the boat instead of sending a rescue crew to the scene.

"The helicopter crew should be at their base, they should be available - that's the point of having that service."

Mr McMillan praised the response of the RNLI, however, which is a separate organisation to the coastguard.

Faulty equipment and confusion over terminology used by people coordinating the rescue contributed to a total delay of around 49 minutes, the MAIB said.

Investigators also found a series of issues with life-saving equipment aboard the Louisa.

"There was nothing on their side that night - the lifejackets and the liferaft just did not work," Mr McMillan said.

A CO2 cylinder inside the Louisa's life raft intended to help it inflate in an emergency was empty and had not been refilled during a recent refurbishment.

This left the crew floating in open water with what may have been faulty life jackets. The life jackets should have kept the men on their backs and their airways clear, but all three men were found dead face-down in the water.

The MAIB said their failure raises serious questions about the effectiveness of safety tests.

It also found the skipper and crew had worked themselves to exhaustion before the sinking, pulling 20-hour shifts for four days straight.

An alarm intended to warn them about flooding had been disabled because it annoyed the crew and they did not wake up until the Louisa was already sinking.

The MAIB found she foundered after her hold flooded with water, probably from the deck wash hose which had been left running by the exhausted crew.

Mr McMillan said his brother was not responsible for the crew's long work hours.

"Fishermen are not guaranteed a wage so the crew take advantage of the opportunities to work and earn when the weather is good," he said.

"They make the most of it while they can. Fishermen are self-employed - if you don't work you don't earn."

"Paul was fair to everyone. He never worked any crew member harder than himself."

The Maritime and Coastguard Agency said saving lives at sea is its "highest priority".

"We strive to ensure that our search and rescue techniques are continually reviewed in order to deliver an effective and efficient emergency response," a spokeswoman said.

"Sadly, the MAIB report highlights a very unfortunate set of circumstances which led to this tragic incident."