Similar topic : Seaworthiness of a ship
All in all, engines are an important part of a ship, but their importance varies comparing a motor and sail boat. For this post, I will focus on engines being a part of sail boats. Nevertheless, sail boats could aim not to have engine power. In definitive, this would decrease their overall weight and increase their overall room for stowage, for example. However, you will be at the mercy of weather conditions. So, it is question of trade offs and vessel purpose.
The two most common types are Diesel and Gas engines. Typically, for sail boats it would be good to aim for a average of 3 to 4 horsepower per ton of the ship weight. This ratio is good as it allows the ship to keep steady course in choppy waters or very stormy conditions, for example. The average life expectancy of a marine gas engine is about 1,500 hours and a marine Diesel engine is approximately 5,000 hours. Both engines have their purposes, to illustrate, if you know that your vessel will be using engine power for an extended period of time, then it is noted that the Diesel engine is better suited for this expectation. Also, if you are sailing with a Diesel engine aboard then there is a very high probability that the engine will last the life time of the boat.
A study conducted by John Vigor showed that the average shipowner who uses the boat on the weekend and for small vacations logs around 200 engine hours a year. If this is the case, then it would take around 40 years to do 8,000 hours (life expectancy of a new generation engine). Once you've passed that cap it will be time to do major changes on the engine.
Both Gas and Diesel engines have their own virtues. Thus, it is always a plus to write down the number of hours you run your engine. This simple task can help you know when oil changes have to be done or when important maintenance is due. Equally important, the maintenance aspect has a lot to do with the actual access to the engine itself. If it is difficult to access this will give a higher expectancy of it being neglected.
In parallel is fuel consumption by weight. Gasoline weighs about 730 grams per liter. Thus, an inboard gasoline engine will need 545 grams of fuel to produce one horsepower for one hour. In comparison to Diesel engine which weighs about 840 grams per liter. This engine will need about 365 grams of diesel fuel to produce one horsepower for one hour. Thus, depending on what type of voyages you are willing to do, it is good to know which is more economical.
In contrast, today there is a bigger presence of engines with flexibility in fuel source. This concept has some importance has it is related to cost effectiveness measure for marine propulsion, and is a developing innovation with the rules and regulations regarding marine emissions. The main purpose of these new types of engines is the reduction on green house gas (GHGs) emissions.
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