Oil-Bulk-Ore carriers. These versatile ships can transport cargoes as various as crude oil, grain, coal, and metal ore. They feature simply-shaped holds without exposed hull framework to permit easy cleaning between cargoes of different kinds. Certain OBO's, called PROBO's specialize in carrying oil products (vegetable and mineral) and soft bulk cargo. Efficient participation in the petroleum products trade requires these ships to have epoxy-coated holds. This provision aids thorough removal of a discharged cargo's traces before loading another. Unfortunately, epoxy cannot endure a great deal of physical abuse. So PROBO's cannot carry ore, coal, and other hard bulk cargoes.