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If you want to change your oil by yourself, the first thing to do is consult your owner's manual. It will tell you what kind of oil you should use, indicating the type, grade and viscosity.
However, this information is given for normal, everyday use. It does not take into account your type of sailing or the area in which you sail. So, if you don't use your boat in a very specific way and you sail in a temperate climate, the oil recommended by the manufacturer is probably the best.
