Medium-speed diesels

THE selection of the most suitable type of diesel, for the duty required, is very important and there are a variety of engines from which a choice can be made, e.g. four-cycle normally-aspirated, four-cycle turbo- charged and two-cycle. They may be low, medium or high-speed engines.

Consider a fishing vessel having approximate dimen- sions, 120 x 25 x 12 J ft. (36.6 x 7.6 x 3.8 m.), and a tonnage of about 320 gross and 115 nett. Such a vessel has a fish-hold capacity of 7,000 cu. ft. (200 cu. m.), bunkers 70 tons of fuel, and requires an engine having 600 to 700 s.h.p. For many years, such a vessel was powered by a steam engine, coupled directly to the propeller shafting and running at a slow speed. Such engines gave reliable service, but the modern diesel, which is more economical to operate, can claim to give equal reliability. A fishing vessel is required to be continually in service and the engine is only shut down for a day or two between trips. While at sea heavy weather and storms are often encountered, which demand the utmost reliability from engine and vessel. The following points, therefore, must he considered in choosing an engine:

1. Reliability: a foremost requirement.

2. Simplicity: the men employed to run the machinery are not highly skilled diesel engineers and they want an engine needing the minimum of attention.

3. Maintenance: the engine must be able to run for long periods between overhauls and, when main- tenance work is done, the design should allow pistons and cylinder heads to be removed easily and there should be easy access to all parts for inspection.

4. Size of engine: space taken up by the engine should be kept to a minimum.

5. Economy: the fuel and lubricating-oil consumption must be considered when assessing the merits of diesels for installation in fishing vessels.