Why did Concordia, a modern, recently-inspected vessel, sink? Worse, why did it sink so fast that a ship equipped with the most modern communications equipment, including satellite telephones, failed to radio a distress call?
Modern, steel-hulled, recently inspected ships - even tall ships that evoke an earlier era - aren't supposed to fall over and sink in bad (but not very bad) weather.
Maritime disaster investigators from Barbados - the tiny Caribbean country where the sailing vessel, like thousands of others are registered to avoid the big expenses and tougher rules of countries like Canada - will lead the probe into the sinking.
The questions will be as complicated as evaluating the Concordia's stability, or as simple as why a satellite telephone wasn't in one of the life rafts.
That everyone on board survived still leaves questions unanswered, including why the captain and crew failed to send distress signals; whether the 60-metre-long vessel was properly secured for sailing into a storm and whether it was really struck - as the captain suggested - by a "microburst," an exceedingly rare blast of wind usually lasting only seconds.
Roger Long, a naval architect and expert on stability in large sailing ships, says microbursts have been blamed before - and wrongly - for design flaws in sailing vessels and suggested that investigators take a careful look at Concordia's stability.
Mr. Long was retained as an expert in the inquiries following the sinking of the British sailing school ship Marques in 1984. From a crew of 28, 19 were lost in that disaster, most of them young trainees.
Survivor accounts remain fragmentary, and accident investigators warn it may take months to piece together the sequence that sank the Concordia, apparently in less than 30 minutes.
However, the scenario that a microburst, a powerful blast of wind radiating outward like an upside-down mushroom cloud, knocked the ship down, flat on its side with its masts lying on the sea surface, already seems at odds with some accounts.
Reports indicate that the Polish-built brigantine heeled over in heavy winds so drastically that water started seeping in through large, partially submerged windows, which could suggest both stability problems and questions about the integrity of the windows.
Aside from the ship itself, the performance of captain and crew will come under scrutiny. But the fact that all 64 on board managed to get into life rafts, spend two nights in the Atlantic and survive to be rescued with no serious injuries points to superlative seamanship, at least after the Concordia was imperilled.
There will also be questions about the response time, which left the rafts adrift for 40 hours.
"It doesn't seem unreasonable to me that it took between 12 and 24 hours to get rescuers moving to the scene," said Benjamin Strong, who helps run the Automated Mutual Assistance Vessel Rescue System for the U.S. Coast Guard. It was used to locate the two closest ships to rescue Concordia's survivors.
The distress call from the stricken vessel, sinking in heavy seas 500 kilometres off the Brazilian coast, was sent on Wednesday by an automatic emergency beacon designed to start signalling on immersion. But without a distress call or any two-way communication, search and rescue officials waited, trying to determine if the beacon was a false alarm.
The Concordia's life rafts were supplied with water, biscuits, flares and first aid kits. But why not a hand-held satellite telephone in a Ziploc bag along with a portable GPS?
The Concordia had satellite links and modern maritime radio links in its sophisticated communications room but, survivors said, that gear was flooded.
On Thursday morning, the Brazilians and Canada's search and rescue centre in Halifax were still attempting to contact the ship to determine if the emergency was real. Eventually, a Brazilian long-range Hercules C-130 search plane was dispatched, spotting the rafts and leading two freighters to the place near the last recorded position of the Concordia, where the survivors were picked up on Friday.