Quick Delivery Reduces Drydocking Costs For Navy Bearing Replacement

With drydocking costs sometimes topping $10,000 per day, shipowners take a serious interest in delivery schedules for replacement parts, even when their resources are as vast as those of the U.S. Navy. The problem becomes increasingly acute when replacements can be ordered only after the original parts have been removed in drydock and examined for wear.

This fact came to light with the recent refitting of propeller shaft bearings for the Military Sealift Command tanker Kawishiwi (T-AO-146). One of six Neosho Class oilers, the 38,000-ton vessel has a cargo capacity of approximately 180,000 barrels of fuel oil.

The Kawishiwi's two propeller shaft liners were found to be worn beyond acceptable levels during a recent overhaul at Versatile Pacific Shipyards Inc. in North Vancouver, B.C. The under-size liners made it necessary to replace her two sterntube and two strut bearings with over-size components. The over-size bearings brought the critical clearance between the 21 Vs -inch shaft liners and the bearings back to an acceptable Vs inch.

Normal procurement time for replacement of the original bearings with the same type is 10 days for manufacturing, plus normal shipping time. With the assistance of Vancouver distributor Pacific Propulsion Ltd., the shipyard ordered Thordon XL elastomeric stave bearings from the manufacturer, Thomson- Gordon Ltd. These staves were manufacturered in a one-step molding process and delivered to the yard all within seven days.

Apart from fast delivery, the Navy can expect further benefits from the oiler's new bearings. The material has a coefficient of friction that is less that half that of rubber.

Therefore, at slow speeds, before hydrodynamic conditions are achieved and water becomes the effective bearing surface, less torque will be required to drive the ship.

This will result in reduced bearing and liner wear, quieter running, no "stick-slip" phenomenon, a measure of fuel economy, and longer life for most of the final drive components.

For further information and free literature describing in detail the specifications and applications of Thordon XL bearings, Circle 4 on Reader Service Card

Maritime Reporter Magazine, page 40, Oct 1986

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Maritime Reporter

First published in 1881 Maritime Reporter is the world's largest audited circulation publication serving the global maritime industry.