Shipping firms with self-unloading vessels are benefiting from the use of an ultra-high molecular weight (UHMW) polymer manufactured by Hercules Incorporated to line their cargo hold hoppers. Ship operators that are saving thousands of dollars per unloading hour include many well-known names in Great Lakes shipping, such as American Steamship, Hanna Mining, Huron Cement, Canada Steamship Lines, Algoma Central Railway's Marine Division, Upper Lakes Shipping, Hall Corporation Shipping, and St. Lawrence Cement Company.

In addition, shipbuilding itself is undergoing a revolution in self-unloading hopper designs thanks to the properties of UHMW polymer with molecular weights in the range of three to six million. It has a coefficient of friction approximately half that of steel, providing a non-stick surface that, these shippers point out, greatly facilitates the unloading of cargo even when it is wet or sticky.

This means that materials such as coal, gypsum, and cement flow more easily and reliably than on unlined metal surfaces. It also permits wet material to slide more easily on the plastic's wax-like surfaces. This, in turn, has given them two options: to design steep hopper slopes, or to install liner sheets of 1900 UHMW polymer and reduce hopper slopes.

Normally designed with slopes as high as 57 degrees, hoppers of self-unloading ships can now be angled as low as 37 degrees when the polymer liner is used. The advantages of this reduced slope angle have been proven out along several lines, according to Mentor Dynamics, Limited, Ontario-based fabricator pioneering in this new method of lining hoppers.

Shippers attest to the fact that the lower angle design on the hoppers of their freighters has resulted in several benefits: it increases the weight (or amount) of material that can be carried; and it improves the stability of the ship by making it possible to store this great volume below the vessel's center of gravity.

Some shippers report that their unloading times have been reduced from as much as 48 to eight hours because the UHMW polymer allows material to slide out, not bulk up requiring lengthy times to get the last portions out. Shippers cite average times of 16-20 hours have been reduced to a mere eight, at cost savings of several thousand dollars per trip. An additional benefit is that 1900 UHMW polymer has virtually zero moisture absorbtion; materials slide easier wet or dry.

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