Which of the following is NOT one of the three engine configurations for boats?

The correct choice indicates that "Electric" is not one of the traditional three engine configurations typically recognized for boats. The three primary configurations for boat propulsion systems are outboard, stern-drive (also known as inboard/outboard), and inboard engines.

Outboard engines are mounted on the transom of the boat and are often portable, providing a straightforward solution for many recreational vehicles. Stern-drive engines combine aspects of both inboard and outboard configurations, as they have a drive unit that is external to the hull. Inboard engines are installed within the hull of the boat, making them suitable for larger vessels and providing better weight distribution.

While electric propulsion systems are emerging technologies that are gaining popularity in modern boating, especially with a focus on sustainability and reducing emissions, they do not fall under the traditional engine configurations that have historically been defined for marine vessels. This distinction highlights the evolution of boat engines, as electric options are becoming more recognized but were not traditionally categorized alongside the established configurations.