How many types of marine engines are there?

There are many different types of marine engines. However, they can be classified into three main categories. The first is the outboard engine, which sits outside on the hull of a marine vessel. The second is the inboard engine, which is enclosed inside the hull of the marine vessel. The third is the inboard/outboard motor, or the stern-drive engine, which is mounted inside the boat and has an additional unit that is attached to the transom.