There are basically two types of small diesel sailboat engines, a two cycle engine and a four cycle engine. The two cycle engine is made only in Detroit, Michigan. The four cycle engine is represented by both Cummins and Caterpillar and almost all others. There are substantial differences in each engine with their own merits depending on the application of the engines. Small diesel sailboat engines are complex and each does better with a particular application.
Before we get into this let�s talk about some of the myths surrounding small diesel sailboat engines. The reputation of reliability and very long engine life began over one hundred years ago, however this reputation no longer stands. The engines are based on a very simple and slow turning engine with low horse power. There aren�t many of them in existence. The need of today is the need for speed.
Modern diesel engines are sophisticated, complex, of lighter weight and are very powerful. They last no longer really than any gas engine and probably not as long. They are very delicate. The rule of thumb lately is that the more power you try to get from any given engine block the less service life they will provide.
There are pros and cons to small diesels sailboat engines let�s look at two cycle engines first then we will look at four cycle engines. The two cycle diesel engine uses a moderately heavy cylinder block with complex casting. Compared to the MTU or the Volvo engine it is light. When compared to Yanmar or Cummins it is heavy. The downside to this engine is that the many parts create more serious wear problems This is magnified with poor maintenance. Two cycle engines are favored by commercial boat industry. It has a more immediate power delivery because it needs only two revolutions per minute to reach combustion.
The four cycle small diesel sailboat engines requires four revolutions per minute to come to combustion. It has much fewer and less delicate parts. They do require less care. They must throttle up to higher rpm�s of similar amounts to deliver enough power to the propeller.