NTSB: Ineffective voyage planning led to crane hitting Mackinac Bridge

Not for the first time, the National Transportation Safety Board has issued a report involving a crane, a barge and a bridge. This latest report deals with an incident that occurred on May 7, 2023, when the 1973- built towing vessel Nickelena, operated by Basic Towing, was transiting the Straits of Mackinac, towing a deck barge transporting a crawler crane, when the crane boom struck the main span of the Mackinac Bridge. The contact bent the crane boom backwards, causing the boom to eventually collapse onto the aft end of the barge. No injuries or pollution were reported. Damage to the Mackinac Bridge was estimated at $145,000 and damage to the crane was estimated at $665,000.

The Nickelena was transporting a Terex-American HC 275 crawler crane with a 160-foot-long boom and a 5-foot “rooster” sheave attachment on the deck barge.

Before departure, managers from the towing vessel operating company visually estimated the angle of the boom to be between 50° and 60°. Using their visual estimation of the crane’s boom angle and an estimate of the crane’s boom length, both of which were incorrect, they believed that the boom was at a safe height for the transit. Investigators determined that the actual boom angle was about 62°, corresponding to a boom height of about 162 feet above the water. Given the vertical clearance was 153 feet at the time of the contact, the crane was about 10 feet too high to transit under the Mackinac Bridge. Towing vessel operations are required to have a towing safety management system, or TSMS, which is a formal, documented system for owners and operators to ensure that rules and procedures related to safe operations are in place. Voyage planning would have been included in a TSMS. The vessel owners, Basic Towing Inc., told investigators that they had a TSMS. However, says NTSB, there was no documentation that a navigation assessment was conducted before departure, and the captain took no additional actions to verify the tow was safe to transit the intended route after the towing company managers told him the tow was “ready to go.” The National Transportation Safety Board determines that the probable cause of the contact of the Nickelena’s towed crane on deck barge BMI 209 with the Mackinac Bridge was the captain’s and barge company managers’ ineffective voyage planning, which did not identify the crane being towed was too high to pass safely under the bridge.

Verifying navigation risks when voyage planning: For vessels and tows with high air drafts, such as crane barges, bridges pose a risk of overhead contact. Operators should ensure they have the most accurate and objective data about the crane and bridge heights before getting underway. Appropriate navigational resources such as the U.S. Coast Pilot or navigational charts should be consulted by owners and operators when developing voyage plans to assess navigation risks and hazards, including the air draft relative to bridge vertical clearances along the intended route.