Page 43: of Maritime Reporter Magazine (March 1999)

The Great Lakes ore carrier Herbert C.

Jackson suffered severe damage — four ft. cracks — to its propeller hub. The hub was restored to original specifications using metal stitching. rejuvenate a more than 90 year old

Great Lakes cement carrier. The ship is powered by a 3,000 hp Skinner Uniflow steam engine, one of just two Great

Lakes vessels still operating with this type of power plant. On a return trip from Chicago, the Medusa Challenger developed cracks in the lower heads.

Back in its homeport of Milwaukee, the owners chose to weld the damaged areas. This weld would be no easy task due to the depth of the cracks. Prior to welding, the repairmen ground out the cracks in the shape of a "V", and then filled in the area with weld. The day and night repairs took place on board over 13 days. While welding took place below deck, the entire crew remained busy with painting and general mainte- nance.

The hard work failed to pay off. Once the ship left port, the welds proved unable to hold up to the stresses of oper- ation. Having heard of metal stitching, the owners decided to try the process.

The additional work consisted of drilling a series of holes at right angles to the cracks and then filling the cracks with rods made of a special alloy. In just six days the repairs were completed and the Challenger departed.

Unlike standard welding procedures, the metal stitches held up to the demands of the ship.

Another benefit of the process is the stitch distributes torsional loads away from fatigue points. Precision dimen- sions on the repair parts are tightly held as they are cold repaired — no heat is required. Stitching is permanent, as the repair is stronger than the original metal.

March, 1999

Hub No Match for Crushing Ice

For the Herbert C. Jackson, a Great

Lakes ore carrier, battling the severe shocks of ice-bound water had resulted in 80 in. cracks into the 4-sq. ft. pro- peller blade hub.

Five days of metal stitching and $25,000 brought the hub back into ser- vice. This type of repair for a hub secur- ing 7 ft. blades had reportedly never been attempted before. Estimates for replacing the heat-fitted hub ran to $250,000 and nearly six months of work.

As proof of the strength of the repair, the Herbert C. Jackson set out to

Cleveland in early spring two years after the repair. This time the ice sheared off the propeller blades. After ballasting the tanks to start the repairs, an inspection revealed the hub was as good as new.

Metal Surgery went on to replace the blades.

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