Survey helps ensure safe “parking” for deep-draft vessel in SF

In preparation for the M/V TERN’s anticipated arrival this week in San Francisco Bay, the Coast Guard and Port of San Francisco asked Coast Survey for a bathymetric survey of the proposed anchorage site. TERN is a semi-submersible vessel with a 60-foot draft, and the proposed anchorage site has charted depths of 62 feet and 63 feet ‒ leaving no room for error, to say the least. The question was whether there are any spots shoaler than 62 feet.

This isn’t your everyday anchorage.

“This vessel floods ballast tanks and partially sinks, putting the main deck below water. Items can then be floated onto the ship, and then water is pumped out of the ballast tanks to bring the main deck back above water level,” explains Lt. Michael Davidson, chief of Coast Survey’s Navigation Response Branch. “TERN won’t actually be anchoring in the anchorage, but rather will be held in place with tugs while cranes are transferred. When she submerges during the operation, her submerged depth is 60 feet.”

Coast Survey assigned Navigation Response Team 6 to investigate the depths with its multibeam echo sounder, to ensure that the TERN will have the under keel clearance she needs. Last week, as requested by the Coast Guard, NRT 6 conducted an investigative survey around Whiskey 2, Anchorage 9. (Whiskey 2, depicted on the survey chart as W2, is a “bucket” that resides within Anchorage 9. A bucket is where they usually park a ship.) Of the many small, pocked features, the team found six that exhibit a height above bottom. Most notable of these features is a 60’ shoalest sounding near a 63’ charted depth – near the location where TERN was supposed to submerge.

After the Coast Guard received the team’s report of obstructions, they asked Coast Survey to investigate an additional area. They were looking for a spot that was at least 62′ deep, free of any features.

“In our area of survey near W1, there were no features that exhibited a height above bottom or showed any significant scour,” reports Ian Colvert, acting team lead of Coast Survey’s Navigation Response Team 6. “The area near W1 is a much more promising place to park the TERN, versus W2 which had a few features and depths not as deep.”

Coast Survey has a proud 200-year history of protecting ships from accidents. NRT6 gives us a very real example of how that mission continues today.

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NOAA navigation response teams improve charts for ships transiting Miami and San Francisco

Coast Survey’s navigation response teams, which are 3-person hydrographic survey teams on small boats, have made a fast start on this year’s survey season.

In Florida, where Coast Survey is preparing to issue a “new and improved” Miami Harbor Chart 11468 to alleviate vessel congestion at the Port of Miami, a navigation response team finished final hydrographic surveys to ensure the new chart has the latest and most accurate depth measurements around several areas identified as critical within the port. In just ten days, team members Erik Anderson, James Kirkpatrick, and Kurt Brown acquired, processed, and submitted the multibeam survey data covering 64 nautical miles.

NRT2 Miami survey
NOAA Navigation Response Team 2 just finished up this survey in Miami

The Biscayne Bay Pilots and others requested the new chart, which is reconstructing old charts in order to provide large-scale coverage of the entire precautionary area where vessels congregate to await pilotage and commit to an approach course to the channel. Updating the chart information and expanding chart coverage will alleviate a navigation safety risk for the world’s busiest cruise port, and will protect endangered coral reefs from inadvertent anchorages.

One interesting side note on the Miami survey… The team found a sunken car, which a Miami Police Department Marine Patrol/Underwater Recovery Detail dive team subsequently investigated. It appears to have been there for approximately 20 years, divers said. We understand they retrieve around 50 cars a year, but have never seen one this old. They plan to raise it later this month. Any bets on make and model?

NOAA navigation response team found this submerged auto at PortMiami
NOAA Navigation Response Team 2 found this submerged auto at Port of Miami

Meanwhile, in San Francisco Bay, another navigation response team is planning a special hydrographic survey to update NOAA charts 18656 and 18657. The action comes as a follow up to a July 2013 grounding by a tug and a barge carrying 80k barrels of crude oil in Benicia Anchorage 22, near Carquinez Strait, San Francisco. After the accident, team members Laura Pagano, Ian Colvert, and Edmund Wernicke conducted a reconnaissance hydrographic survey to determine if an uncharted obstruction caused the grounding. The survey determined that shoaling was the culprit and the evidence indicated that a charted shoal has been creeping through the Benicia Anchorages towards the federal shipping channel at Carquinez Strait. Last month, the U.S. Coast Guard requested an extensive survey to determine the extent and significance of shoaling in the Benicia Anchorages, and the team is planning to conduct the survey shortly.

NRT6 survey
NOAA Navigation Response Team 6 conducted a recon survey of area where a tanker barge went aground

NOAA navigation manager Gerry Wheaton suspects heavy sediment runoff from rains over the years have altered the sea floor in navigable areas near the Strait. While the initial NOAA recon survey provided information to notify mariners of the dangers, conducting a full bottom survey to update NOAA nautical charts will provide additional detailed depth information necessary to safely navigate the area.