Forum logo Wasn’t the Itasca making smoke for Earhart to see?

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 few miles.

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.

FAQ by Bob Brandenburg

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