"Ad absurdum per aspera" wrote in message
news:1128698314.891523.188890@z14g2000cwz.googlegroups.com...
> Setting aside the question of whether people that age, some with
> mobility problems, were rushing anywhere, a mass movement (no pun
> intended) to one side of a crowded vessel has caused some bad problems
> in the past. The Eastland tragedy in Chicago lo these many years ago
> (admittedly on a vessel with a history of roll stability issues) was
> probably the worst example.
>
> (Well, that and the Swedish warship from centuries ago whose center of
> buoyancy and center of gravity got crossways with each other on the
> maiden voyage, but naval architecture as a science-based engineering
> field thankfully advanced beyond *that* stage long ago...)
>
> The Eastland was of course significantly overloaded -- perhaps due to
> the legendary transparency and accountability of officialdom in a
> different time and place, rather than to obsolete weight estimates;
> but it made me wonder about the statistical basis of the rules as well
> as about people's average weight. The two go together.
>
> I have no idea what the average adult weighs (the airlines, who care
> the most, might be the best people to ask), but 145 or even 160 seems
> like an odd basis. Nobody would describe me as a conspicuously big
> man, but I'd go 190 in fighting trim (reality, alas, is a bit on the
> winter-survival-ready side of 200) and probably left 160 behind forever
> in the freshman dorm.
>
> Now for the statistical part -- how far do you have to go in the
> distribution to be considered as having a prudent safety margin? Is
> there a reasonable chance that some passenger loads will have more
> people like me, not far enough off average to attract attention but far
> enough off to add up to an overload?
>
> These are not trivial numbers for a fairly small vessel. If chance put
> 48 of me aboard and their design basis assumed 140 pounds apiece on
> average, there'd be an invisible Volkswagen somewhere on deck, with
> implications for the static and dynamic issues of center of gravity and
> balance as well as static buoyancy. Even an average 20-pound mistake
> would mean half a ton. Throw in changes to the weight and location of
> the superstructure, and yeah, you can see how these things can sneak up
> on you while you were obeying the rules and maybe even thought you were
> being prudent...
>
Trouble is on a boat large enough for 48 people 1/2 ton is trivial.
Its only half a cubic meter of water, an amount that can be dumped
into the boat by a single small wave.
Any passenger boat should have large safety margins especially as
weight doesnt carry anything like the penalty it does in aviation.
You mention the Eastland, this was a case in which a ship
designed as a freighter was modified in the shipyard to
be a passenger ship. These mods included adding a complete
new upper deck. No naval arcitect was ever consulted about
the affect this would have on the stability of the ship. the ship was
also grossly overloaded.
She was certified to carry over 2500 passengers but was only
196 ft long and under 2000 tons displacement. In comparison
the Titanic which was 880 ft long and displaced 46,000 tons
was licensed to carry 3500 !
It has been reported that the boat that capsized on Lake George
was originally equipped with a canvas awning but had been
requipped with an enclosed fibreglass covering. This extra weight
high up could have diastrous effects on stability and the fact
that the boat was operating illegaly with only one crewman
aboard suggests a cynical disregard for safety.
Keith
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