John wrote - in part....
John Denker via Phys-l <phys-l@mail.phys-l.org>To:Forum for Physics EducatorsCc:John DenkerMon, Mar 29 at 4:12 AMHi Folks --
There are some amusing physics calculations that one can do that
shed some light on the Ever Given / Suez incident.
It must be emphasized that I am not claiming to say anything about
the cause of the accident. A proper investigation takes time. The
initial reported facts are often wrong.
Even so, there are some calculations we can do that involve basic
physics principles that apply no matter what, in this situation
and many others.
1) Crosswind is a topic that has come up. So let's calculate the
force. The formula is:
F = ½ ρₐ vₐ² Cd Aₐ
where
F = force
ρₐ = density of the air
vₐ = crosswind component of velocity (relative to ship)
Cd = coefficient of drag
Aₐ = broadside area exposed to air
In some sense this formula implicitly defines Cd, but it's better
than that, because Cd is more-or-less independent of the other
factors on the RHS.
The Cd for a big flat plate is on the order of 1 ... in contrast
to a streamlined shape, which would have a much smaller Cd.
Reported peak gust was 50 km/hour. That's only 27 knots. That's
windy, but not astonishingly so. I've dealt with lots worse.
Again, beware the initial reports are often wrong. I calculate
a force of 250 tons.
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It looks like John was doing the numbers for a broadside wind or gust.I estimated a wind force around 90 tonnes for 27 kt wind broadside using my assumptions.I wanted to check the wind vector, but I could not find the wind direction there on that day.I fell back on the seasonal wind there for March, a hot dry wind from the south or southwest that carries lots of dust, making visibility sketchy.I notice there is a nominal speed limit in the canal of around 8 or 9 knots, but apparently, this is often exceeded. The Ever Given was clocked at 13.5 kt in the 30 minutes preceding the stranding.Even stranger, there are one or two reports of the vessel veering to port and coming close to the West side of the canal, then veering back and stranding on the East side, and swinging by the stern.The canal is tidal but the water current is moderate - about 2 kt, exceptionally 3 kt according to the (US) Sailing Directions.A shoal patch on the east side where the bows stranded was visible in published photos, and I got the impression that shoals of this kind are not extraordinarily rare.Other vessels of the Golden Class like Ever Given are known to passage through the Suez.