A4 even has its own Wikipedia page
The Universal Atomic 4 is a four-cylinder, 64.46 cubic inch, 30 horsepower (22 kW) gas engine produced by the Universal Motor Company between 1947 and 1984 for use as auxiliary power on sailboats. Over 40,000 of the engines were produced during that time, with an estimated 20,000 still in use today. This "workhorse" engine dominated the expanding sailboat market starting in the 1960s, and between the years of 1965 and 1975 they were installed on up to 80% of new sailboats in the 25-40 foot (7.6-12 meter) range. Their longevity and reliability is proven by the fact that thousands of sailors still depend on the engine, even multiple decades after the Universal Motor Company ceased production.