Tough tug stern gear for tough tug requirements
Ontario-based Thordon Bearings has supplied stern gear to four new tugs that are designed to meet recently introduced US Coast Guard (USCG) rules while also capable of operating in particularly tough abrasive water conditions.
Construction of the 20.4m long by 8.5m wide vessels has been entrusted to Master Marine of Bayou La Batre, Alabama for Waterfront Services of Illinois and are designed to meet requirements of Subchapter M, a set of federal rules recently introduced by the USCG relating to inspection requirements for towboats including seaworthiness standards and safety protocols.
Mitsubishi main engines develop 1,606hp in total driving four-bladed stainless-steel propellers through Twin Disc 5:1 ratio reduction gearboxes. The vessels will work 24/7 on the Mississippi River, operations in very abrasive water conditions frequently operating close to river banks in shallow water depths. This presents challenges for the stern gear and associated bearings and Waterfront Services previous experience of Thordon products was an important factor for selecting the bearings including up to 60,000 to 70,000 hours of trouble-free operation with some of the tugs in its fleet.
Thordon was therefore contracted to supply its RiverTough propeller shaft bearings (for 6” diameter shafts) along with: hardened shaft sleeves; SXL bearings for main and flanking rudders; TG100 tailshaft seals and ThorPlas Blue steering linkage bushings.
The RiverTough water-lubricated bearings were developed specifically for use in abrasive-laden dirty water such as that found in the Mississippi. When used in conjunction with hard-coated nickel-chrome-boron shaft sleeves and a TG100 shaft seal, Thordon state the arrangement can last twice as long as rubber bearings.
The seal uses high-quality, hard wearing silicon carbide faces and Thordon’s proprietary elastomeric polymers to offer optimum combination of strength and stiffness along with flexibility and elasticity. The seal requires no routine maintenance and is equally at home in clean water.
Thor-Blas-Blue bearings are designed for a lifetime of grease-free lubrication and typically specified to replace greased bronze bearings in virtually all steering and deck machinery applications.
Jim Bright, Thordon’s USA business development manager said: “Thordon’s range of river towboat systems offers outstanding wear life in abrasive waters. Any extra up-front cost is quickly offset by longer wear life and reduced maintenance down time over the life of the vessel.”
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