My first exposure to outdraft was the Marseilles Dam accident. Four tow boats were working together to try to get a 14-barge tow out of a flood current and into the safety of a canal as illustrated below.
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| US Government |
The Dale A. Heller towboat was 128 ft, 596 gross tons, and 5,600 hp. The Loyd Murphy was from a 15-barge tow that had already been tied up to a mooring to ride out the flood waters. The Creve Coeur and City of Ottawa towboats were from the Coast Guard.
The Marseilles Dams' gates were almost all of the way open to avoid flooding Marseilles. The four towboats were not successful in fighting the resulting outdraft. And Marseilles ending up getting flooded anyhow.
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| US Government |
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| US Government |
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| US Government [That was the USACE Hercules crane, a Manitowoc 60' ringer.] |
And even after the flood subsided, shipping had to evacuate the pools above and below the dam while a rock cofferdam was being built to allow repairs of the damaged trunnions.
The second demonstration of the force of an outdraft was when I visited Lock and Dam #18 on the Mississippi River last Fall (of 2013). Unfortunately, it was BC (before camera), so I don't have any pictures. So I'll use a satellite picture. Below is the upstream guide wall and upstream gate.
The red rectangle represents the leading part of a 15-barge tow. The blue oval highlights a towboat that is normally parked near the upstream gate of the lock. The blue rectangle illustrates where the "blue" tow boat positions itself while the tow approaches the lock entrance. As soon as the front of the tow is past the end of the guide wall, the auxiliary towboat pushes the tow against the wall so that it is not pulled away from the lock entrance by the outdraft. I left when the tow was close to the lock because I had to leave for a meeting. I assume that as soon as the front of the tow entered the lock, it pulled away and went back to its parking spot.
2022 Update:
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| Pickwick Lock Screesnshot @ 1:08 M/V Frances R Keegan departing the lock, headed upbound. Great job by the entire crew. The timelapse video is a bit long, but is worth watching til the end. It will give you a perspective of how dangerous towboatin' can be. If an engine stalls/fails once they get above the protective walls, they could end up in the spillways. Watch how the current draws the towboat and tow to the port (left) in the video. The captain of the towboat had to use all of the towboat's power to overcome the draw of the river current toward the spillways in the dam. 🎥H.Soto & R.Boyd Pickwick Lock [They have had a lot of rain and a comment indicates the Pickwick Dam is spilling 200,000 cfs. At the end you can also the water level in the lock go down.] |
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