i've got two yanmars in my sailing catamaran....and i gotta say i would NEVER buy them again...the spares are extremely expensive and in the USA you are locked into franchised dealer prices,EVERYONE in a region gets the parts from them so price is virtually fixed,the smaller two cylinder engines are over complicated and if you don't change the oil on them as regular as clockwork they wear out very quickly,i don't expect to get 5000 hours out of my engines,which for a boat is not very good.
they also have a tendency to eat V belts unless the pulleys are kept scrupulously clean,the pulleys are also the cheapest pressed steel going so rust at the first sign of moisture........just my hands on observations........keith