Mirage: Our Lying Eyes!

Mirage: Our Lying Eyes!

By George Papabeis, Flotilla 74 Brandon

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Storyblock image. License for use paid.

“I

see them!” We all did- all three crew and the coxswain of the Coast Guard Auxiliary vessel “Lady E.” We had back-tracked to where we lost sight of the dolphins protec�ng the infrastructure of the Skyway bridge in Tampa Bay, Florida. No one voiced it, but something was off. We could see the dolphins but...

Earlier in the day of July 14, 2018, we measured the height of the dolphins at twelve feet from the surface of the water using a smartphone app that had

The Skyway Bridge dolphin that we measured. Note the concrete cap.

been calibrated dockside from midship using a yards�ck. Gene Keller, the coxswain, plo�ed a course at a 90 degree angle away from the bridge at a compass bearing of 60 degrees. Crew members included George Papabeis and Jeff Gines both from Flo�lla 74 Brandon, and Stanley Clark. We then watched to see when the dolphins disappeared over the horizon. Why were we doing this? To measure the curvature of the earth.

We logged our course as follows:1) 12:55 (hours)27.37.36 N, 082.39.49 W

Measured Dolphin with cam measure iPhone app 12 feet to top of wood bumpers. Proceeded at 20 knots to a compass bearing of 60 degrees. Big Bend power plant smokestacks used as visual for reference.

2) 13:08 (hours)27.38.86 N, 082.37.15 W, 2.56 NM

Stopped vessel and took a reference photo with dolphins s�ll

(Con�nued on page 13)

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MEMBER FOCUS

Mirage

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Inferior mirages

South side of bridge inferior mirages giving the appearance of “floating” dolphins. This photo was taken at the “track back” posi�on.

North side of bridge inferior and superior mirages obscuring most of the dolphins except for the concrete caps. This photo was taken at the “track back” posi�on.

visible.3) 13:16 (hours)27.39.82 N, 082.35.67 W, 4.2 NM

Stopped vessel. Dolphins are no longer visible.

4) 13:19 (hours)

27.39.72 N, 082.35.83 W, - 0.17 NM

Back-tracked along route �ll tops of dolphins visible again

When we back-tracked, we could see the dolphins on the south side of the bridge, but the north side presented the concrete caps floa�ng over the surface of the water. No one said anything but you could almost hear everyone’s brain clunking away in “incredulity mode.” What were we looking at?

The earth curvature calculator at www.omnicalculator.com puts 2.5 feet obscured at a distance of 4.2 nau�cal miles (NM) at an eyesight level of six feet. For 12 feet (the dolphin’s height) to be obscured, the “Lady E” would have to have been 6.3 NM from the bridge. What was causing our dolphins to disappear from eyesight before they should?

The answer lay in a combina�on of inferior and superior mirages. Imagine a mirror on the ground. The reflec�on would be the inferior mirage. A superior mirage would be the opposite. The two can occur at the same �me and can vary in intensity, size, and placement on the horizon. We witnessed this on the “Lady E” when

(Con�nued on page 14)

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