I sailed with a Doxford 56LB4, a so called Opposed-Piston Engine, which was not exactly a success. It was found the hard way that these contraptions were unsuitable for the tanker trade. The harbor layover time for tankers were too short for the extensive maintenance which they required. This resulted in many breakdowns during the voyage which often caused unsafe situations. An advantage was the extreme low fuel consumption of 6 (!) tons per day.