Slop tanks are the focal point of the Load-On-Top system used on crude oil tankers to prevent pollution of the sea. Design of these tanks and their operating procedures strongly affect the degree of oil-water separation achieved. This paper presents the results of an investigation undertaken to define designs and procedures for improving separation and minimizing oil discharge to sea. The program was funded in part by the U.S. Maritime Administration.

Based on tanker experience and laboratory tests with tank models, guidelines on capacity, structure, inlets, outlets, system design, and wastewater handling, procedures were developed. The guidelines aim at assuring successful Load-On-Top operations by (1) providing tanker operational flexibility for handling oily water, (2) minimizing the degree of oil-water mixing, (3) avoiding re-dispersion of separated oil during feeding and discharging operations, and (4) eliminating the possibility of accidental oil contamination.

This investigation provides a basis for future large-scale or shipboard studies to improve the performance of slop tanks on existing tankers as well as on future tankers.

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