Here is a summary of what we know about Itasca and her smoke generation
on the fateful morning.
Itasca was 250 feet long, painted white, and was steam-powered
by two Babcock and Wilcox boilers that burned fuel oil. More later about
the properties of that fuel.
According to her deck log, Itasca was “drifting to westward of
Howland Island” just a few hundred yards offshore, began “laying down heavy
smoke” at 06:14 local when Earhart was estimating that she was 200 miles
out, and the smoke was observed to “stretch out for ten miles and not thinning
out greatly.” There is no log entry indicating cessation of the smoke.
0614 local time was about an hour and a half before Earhart was expected
to arrive at Howland.
During the next two hours, Itasca’s weather log reports wind direction
as East, with speed varying between 7 and 11 knots.
It is worth noting that Itasca’s estimate of the length and density
of the smoke is not credible. Consider that since the ship was drifting,
the ship’s view of the smoke was along the axis of the smoke plume, which
was drifting downwind. Consequently, it would not have been possible to
estimate the length of the plume, or its downstream density.
The boiler fuel oil most commonly used in those days
was known as “bunker
oil”, which essentially was crude oil right out of the ground – very heavy
with a high soot content, and hard to burn; it required extensive preheating
just to get it to atomize properly in the boiler feed nozzles. It was somewhat
like burning liquid tar. The smoke therefore was “heavy” and tended to
sink rapidly to the surface. During and after WW2, the Navy switched
to Navy Special Fuel Oil (NSFO) which was processed so that it was easier
to preheat and burned more efficiently, producing a somewhat lighter smoke.
It is unlikely that Itasca was burning NSFO.
Even NSFO smoke screens are not very durable. In anything more than a
light breeze, say 5 knots or so, the smoke is pushed rapidly down onto
the surface where it flattens and thins out within three to five miles.
This results in rapid vertical thinning of the smoke, thus drastically
reducing its visual contrast with respect to the sea surface.
So, within about five miles from the Itasca, the smoke plume would
have been virtually invisible from the air. Smoke is really only useful
as a visual detection aid when the wind speed is less than about 5 knots,
when there is a significant vertical plume, which is readily visible in
contrast to the sky luminence.
AE’s problem was further complicated by the fact that at the reported
wind speed, there would have been white capping, a condition in which the
wind-driven waves break like surf on a beach. The fact that Itasca was
painted white and was relatively small would make her tend to blend in
with the whitecaps, and make her nearly invisible from the air beyond a
If Itasca had been steaming at 10 knots or so, her Kelvin wake
(the vee-shaped wave pattern caused by the ship’s movement throught the
water) would have been quite visible from the air, looking like an arrow
pointing right to the ship. But the drifting white Itasca would
have been nearly invisible unless AE was within a very few miles.
Furthermore, it is unlikely that Itasca made dense black smoke
for an hour and a half, which would have been necesssary for AE to have
a chance to reach and see the smoke plume.
In a steam powered ship such as Itasca, under
normal steaming procedures, the boiler watch crew would take particular
care to ensure that the fuel-air mixture being sprayed into the boiler
fire box was as close as possible to ideal, so that combustion would
be nearly complete, thus minimizing soot buildup on the tubes within
which water was boiled into steam within the boiler firebox. The combustion
exhaust observed at the smoke stack under ideal conditions was described
as a “light brown
haze”, and was not visible from more than a mile or so. In order to minimize
soot buildup on the boiler tubes, the ship would “blow tubes” once each
four-hour watch. This was accomplished by activating a valve system which
literally sprayed live steam onto the boiler tubes in the firebox, thereby
dislodging loose soot from the tubes. The dislodged soot was carried up
and out the ship’s smokestack by the exhaust gas plume.
But there always was an accumulating residue that could not be removed
by blowing tubes, and eventually, about every 600 steaming hours or so,
it was necessary to shut down each boiler and (after it had cooled!!!)
send sailors into the fire box to remove the residual soot by hand, with
wire brushes, etc.
Since Itasca had only two boilers, the Captain would NEVER have
taken a boiler off line for tube maintenance while at sea, even though
one boiler would suffice for the ship’s needs while on station, because
if the on-line steaming boiler were to sustain a major casualty requiring
it to be taken off line, the ship would be dead in the water with no power.
So, cleaning fire box tubes (known as cleaning firesides) was done in port,
not at sea.
A smoke screen was created by reducing the amount of air in the fuel-air
mixture being pumped into the boiler fire box. This made a lovely black
smoke, but rapidly increased the rate of deposition of soot on the boiler
tubes, thus hastening the time when it was necessary to shut down the boiler
for hand cleaning.
And making heavy black smoke for a protracted period – more
than 30 minutes or so – was inviting trouble in the form of a tube rupture
(caused by uneven heating of the tube surface due to rapid and uneven soot
accumulation) which resulted in water and steam spewing into the fire box,
dousing the fire and, worse, causing the firebrick lining the inside of
the fire box to crack from chill shock and crumble into a pile of rubble
in the middle of the firebox. Such an event would require major and expensive
shipyard repairs, and avoidance of such a failure was uppermost in the
mind of any ship Captain.
To have laid black smoke until AE’s scheduled arrival at Howland would
have been courting disaster, and there is nothing on the record to indicate
that Itasca was under orders to incur such a risk.
So there you have it. Itasca almost certainly was not making black
smoke when AE needed it, but even if the smoke was being laid right up
to AE’s estimated time of arrival, AE wouldn’t have seen it until she was
just a few miles away.