Luck...? Whilst it is useful to understand the general reasons for accidents, reading the above, anyone would think the sudden drowning of up to a thousand people within half an hour was an everyday occurence.
Quite the contrary. Most vessels are
not operated in waters they weren't designed to negotiate. Few people (and fewer sane ones) would attempt to paddle a rubber raft around Cape Horn, or steam a Carnival Cruise ship down a class 4 rapids. The pontoon party boats on the lake a mile north of me are never seen in the salt-water bay a mile south from me. The center-console sport-fishers popular on that bay are never seen on the shallow lake. The most capable Mississippi Riverboat would be at high risk steaming between Caribbean Islands, but the most seaworthy ocean ferry wouldn't do very well on the Mississippi either.
Most vessels are
not operated in all weather conditions. This is mostly true for pleasure craft (most of those, here in New England, are in storage all winter, for instance) but commercial ships have limitations too. Even a year-round fishing vessel will put into port for a nor'easter, and even the biggest cargo ships will divert around a hurricane. This is especially true when that first factor is in play, i.e. the vessel is less than ideal for the marine environment. When Harbo and Samuelsen rowed the skiff
Fox across the Atlantic Ocean in 1896, it was in summertime. (And even so, they ran into a storm and capsized, and barely survived.)
I can't say for certain that most commercial vessels are well maintained. Many are, but many others aren't. As far as I can tell, that's an issue throughout the industry. But the investigation findings regarding the final operating conditions of
Estonia, especially the bow mechanisms, show that it was unusually poorly maintained.
Most vessels do
not steam with marginal trim (imbalance along the port-starboard axis) conditions. This is known to be extremely hazardous. A list, or a need to max out the trim adjustment system to avoid a list, means the vessel is already on the verge of capsizing. Leaving port in that condition is like setting off in a plane with a known fuel leak ("but it's only a slow leak and the tank's full now").
Most commanders
do recognize and take into account that the severity of the effects of wind and wave conditions on the ship depends on the vessel's course and speed. During the age of sail, surviving a storm sometimes required a ship to run downwind, even if that meant going hundreds of miles out of the way (and heaven forfend any lee shore in the path)! In extreme weather conditions even modern vessels must change course or slow down. The weather on the night of the sinking might not have been extreme for the Baltic Sea, but (remember that first factor?) was quite extreme compared to the operating conditions the hull was designed for. Very large Baltic Sea waves travel at about 40 knots, while
Estonia steamed at about 20 knots. The bow-on impact would have therefore been about three times faster than a stern impact ((40+20)/(40-20)) and about nine times the kinetic energy compared to a following sea. (If the actual waves were a more ordinary size for the Baltic Sea, then they were also slower than 40 knots so the differential between bow and stern impacts at a 20 knot flank speed was even greater. For instance, ((30+20)/(30-20)) which is a fivefold difference in speed and 25-fold in kinetic energy.
Short of turning around, a 5-knot reduction in speed would have reduced the kinetic energy of the impacts considerably. If the waves were 40 knots, 16% less kinetic energy. If 30 knots, 19% less. The bow faring might have survived the crossing (most likely, to fail some other day if nothing else was done, but that's still a better scenario).
Most ships
do have vigilant crews, at least in adverse conditions. Self-preservation is a common concern. The seeming indifference to same among the
Estonia crew is to me the single strangest aspect of the disaster.
We do not expect such sinkings every day because like I said, the key here is the
accumulation of adverse factors (and, as JayUtah has been expertly pointing out, the concomitant
erosion of safety factors). One ship might be in poor repair but operated cautiously. Another might be poorly designed but well maintained. Another might set an aggressive course in bad weather but the alert skipper and eager crew responds expertly to every anomaly and every potential hazard to keep the ship safe. All those ships will almost certainly survive. The problem with
Estonia wasn't one thing going wrong, it was everything going (and being done) wrong at the same time.
And while not a daily occurrence, sinking of oceangoing vessels is more than a weekly occurrence, for the reasons JayUtah explained. Most don't drown 1000 people, of course, but that's for many reasons, including the fact that most oceangoing vessels don't carry 1000 people, and most that do have far better passenger safety systems than Estonia did.
[*]The Captain of nearby Silja Europa said the weather was normal for that time of year
So? Snow is normal this time of year in New England, but if you go out driving in it, and you don't take precautions like slowing down and using snow-capable tires, you'll more likely to end up in a ditch (or worse). What's normal doesn't matter, whether your equipment your usage of it are appropriate for the actual conditions does.
[*]The Captains of Viking Mariella (Thoresson) and Silja Europa (Makela) confirmed the three vessels were travelling more or less side by side to Stokholm as per normal
So? Were the other vessels designed to operate in those conditions? Were they in good repair? Did they have proper trim? Were their crews vigilant? If so, they were not subject to the same
cumulative risks as
Estonia was.
[*]Captains Thoresson and Makela confirm they could see each other.
So? What do their romantic lives have to do with conditions at sea?
[*]Neither of these Captains mention a 'strong wave' or any such 'super wave'
So? If your ship is weak, all waves are strong. It doesn't take a super wave to break fatigued metal. The specific wave that displaced the visor might not have been any larger or stronger than the ten or 100 previous waves. The straw that breaks the camel's back doesn't need to be heavier than the other straws.
[*]On approaching the stricken vessel, Capt Makela said he was shocked to not see any sign of it at all, as would be normal in a sinking ship.
Normal in a sinking ship? What's normal is for a ship not to sink, as you yourself pointed out earlier.
So ascribing sweeping generalisations into a specific case, where we know many of the details, just doesn't succeed in hand waving it away.
It's those details that tell us the ship wasn't designed for the open Baltic Sea, that it was in poor repair, that it was in poor trim, that it steamed at flank speed into the waves without altering course or slowing down, and that the officers and crew acted indifferent not only to the conditions but also to the early signs of things going lethally wrong.