The outboard motor boat is one of the most common boat classes. Unlike inboard boats, having their engine inside, on the ouboard yachts engines are mounted on the outside of the stern, allowing more interior space on relatively smaller boats. Outboard engines can reach very high performance compared to their weight. They provide ease of installation, use and maintenance. Maintenance intervals are quite long. They are divided into two main types: double-stroke and four-stroke. The difference between the two types is not as clear today as it used to be, both having similar values in terms of reliability, weight, speed and consumption efficiency.