What is the nautical term for a small boat that is often towed by a larger vessel?

The nautical term for a small boat that is often towed by a larger vessel is indeed "dinghy." Dinghies are typically small boats that can be used for various purposes, such as a lifeboat, a tender for a larger boat, or for short-distance sailing. They are designed to be lightweight and easily maneuvered, which makes them suitable for towing.

In contrast, while a yawl is a type of sailing craft with two masts, it is not specifically characterized by being towed; it's more often used for independent navigation. A ferry is a larger boat or ship used to transport people and vehicles across water, often on a fixed route. A barge is a flat-bottomed boat primarily used for transporting cargo on rivers and canals, and it typically does not fall under the category of a small boat designed for towing purposes. Therefore, "dinghy" is the most accurate term for the smaller vessel often towed by larger ships.