SIEV 358 tragedy preventable: coroner

The West Australian coroner has found Australian and Indonesian authorities need to improve how they communicate when responding to asylum seeker boats in distress.

A coroner's report into the sinking of the Siev 358 will be handed down on Wednesday.

Western Australia's coroner Alastair Hope has ruled that people smugglers contributed to the deaths of 17 asylum seekers bound for Christmas Island last year.

It's presumed another 85 people also died, but their bodies were never found.

Mr Hope was examining Australia's and Indonesia's response to calls from the asylum seeker boat as it made its way to the island from Indonesia.

The coroner said their boat was overcrowded, it was understandable they called for help on their first day on the open sea and their deaths were accidental.

He recommended that Australia improve its communication with its Indonesian search and rescue counterpart.

He said Australia did not ask Indonesia how it would search for the asylum seekers when it handed the country responsibility for the search.

He also recommended all classified information about any future tragedies be given to police without them having to request it.

For what's known about the fate of SIEV 358, read this backgrounder.