The Swedish ship Poseidon rescued 130 people from a rubber dinghy and another 442 people from a wooden boat found drifting off the Libyan coast on Thursday. Fifty-two people were found dead in the hold of the wooden boat.
The number of dead has varied in reports - with initial estimates putting the figure at 40
- and the Swedish coastguard said on Friday that difficult conditions had initially made it hard to get an accurate number.
"It [Poseidon] is due in Palermo around 8:00 pm (1800 GMT) tonight," coastguard official Robert Primus told AFP.
"Now they have been able to get into the hold properly and count and there are 52 dead," he said.
"The vessel has all the survivors and dead on board, and all of them will be taken off the ship tonight," Primus said.
The Swedish vessel was in the area as part of the EU border agency Frontex's search and rescue mission known as Triton.
Poseidon is expected to leave Palermo for Valletta later Thursday, Primus said.
Calm weather this week appears to have encouraged the smugglers to get as many people as possible out to sea, knowing that, in most cases, they will be picked up by Italian or international boats and taken to Italian ports.
More than 110,000 migrants have so far landed at Italian ports this year. A further 160,000-plus have arrived in Greece.
But at least 2,300 migrants have died at sea this year during attempts to reach Europe, almost invariably on overcrowded boats chartered by people smugglers.