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MARMC Divers Perform Emergent USS San Jacinto Blade Change Outs

Navy News Service

Story Number: NNS151231-06
Release Date: 12/31/2015 1:15:00 PM

By Shelby West, MARMC Public Affairs Specialist

NORFOLK, Virginia (NNS) -- One port-side blade and two starboard-side blades were damaged during a standard training exercise. Rather than replacing all three blades, two of the three were repaired.

Propeller blades have different codes. Alpha-coded blades are only used in a specific set, where individual bravo-coded blades are interchangeable within any set. Divers worked with bravo coded blades on San Jacinto, therefore only having to change out three blades instead of the whole set.

'New blades are incredibly expensive -- in order to save money, we called Wӓrtsilӓ, a group of coded welder contractors, to make small welding repairs onsite,' said MARMC Dive Team Charlie Supervisor Chief Navy Diver John Marsack. 'The prairie air channel on one blade had to be repaired and there was a one-inch cut that had to be repaired on another blade.'

Repairing and installing the blades on San Jacinto was a joint effort between MARMC divers, Naval Sea Systems Command Supervisor of Salvage and Diving (NAVSEA 00C), Emergency Ship Salvage Material (ESSM) technical experts and Wӓrtsilӓ.

'The biggest challenge is working with so many different entities to meet the timeline,' said Navy Diver 1st Class Brian Bennett. 'Fortunately, we are still running ahead of schedule.'

Most Navy ships now use hex bolts to secure propeller blades however, San Jacinto's blades are secured by Morgrip bolts, which require additional steps to loosen or tighten them.

'With hex bolts, we can send down a high torque and the diver can loosen or tighten each bolt with one tool,' said ESSM Maintenance Mechanic Joey McKee. 'Morgrip bolts have a hydraulic power head. A bullet rod must be inserted in each one and it has to be hydraulically charged to stretch it. Each bolt must be sent down one at a time. The diver tightens a bolt at a pace of one minute per turn, allowing all the hydraulic fluid to come out. The pressure is relieved and it allows the bolt to compress, putting tension on the blade palm in order to torque it.'

The torqueing process is more time-consuming for Morgrip bolts than it is for hex bolts.

According to McKee, 'A diver has to send the power head up to the surface each time. It takes three minutes to charge the power head to 35,000 pounds per square inch before it is sent back underwater and additional time to screw it in and bleed the pressure.'

'The damages to San Jacinto's blades were not normal wear and tear,' said Marsack. 'They had to be fixed quickly not only for security purposes, but when the blades aren't running at max efficiency, it causes the ship to burn more fuel.'

Out of MARMC's six dive teams, Charlie has the most experience with propeller blade change outs.

'Charlie has become the unofficial blade team at the command,' said Marsack. 'Our experience allowed us to finish ahead of schedule.'