The South African yachtsmen – Anthony Murray, Reginald Robertson and Jaryd Payne – were en route to Thailand to deliver a catamaran when all contact was lost on 18 January during cyclone Bansi, which passed very close to the yacht.

Since then, there have been several sightings of what is believed to be the upturned catamaran. The first was on 21 May, when a ship reported sighting an upturned hull 583 nautical miles south east of Port Louis, Mauritius. The second was on 5 June, 552NM south east of Reunion Island and at the co-ordinates 27 51.7S 063 01.6E.

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“We are very grateful for everything that the maritime authorities are doing – and have done – for us over the past four months,” says Diane Coetzer, spokesperson for the family group and Anthony Murray’s sister in law.

“However, we cannot sit back and wait – not when we still hold onto the hope that Jaryd, Reg and Anthony have somehow made it through this nightmare and are alive in the hull. We urgently need to establish if this is indeed the hull of the catamaran our loved ones were sailing to Phuket, if anyone has survived in the hull, and whether the liferaft has been deployed,” she said.

“We are also looking for answers to the many questions we have about the voyage. This is an expensive effort that requires the help of experts and is not something we ever imagined would be left to us, as the families, to do. But we will do anything we can to find our guys.”

The families are using global fundraising website, www.gofundme.com, to raise money for the campaign, called “South African Crew Lost at Sea”.