New Hampshire Boating Practice Test

The steering device referred to in this question is the rudder, which is typically a vertical blade that is attached at or near the stern of a vessel. The primary function of the rudder is to control the direction of the boat when it is in motion. When the rudder is turned, it creates a difference in water pressure on either side of the blade, causing the vessel to turn in the direction opposite to where the rudder is pointed.

This design is fundamental to the steering mechanism of many types of vessels, providing precise control over navigation. Other types of vessels mentioned in the options—such as multi-hulls, flat-bottom hulls, and deep Vee hulls—do not denote specific steering devices but rather describe the overall shape and structure of the hull. While these vessels may also utilize rudders for steering, the key distinction in the question is the specification of the steering device being a vertical blade at the stern, which unmistakably identifies the rudder as the answer.