Final answer:
Boats over 9m and up to 12m must have a buoyant heaving line at least 15m in length as part of the required safety equipment. The other options, like radar and a sound signaling device, are not specifically required for boats of this size, although a sound signaling device is commonly required.
Step-by-step explanation:
The question relates to the safety equipment required on boats between 9m and 12m in length. Among the available options, boats over 9m and up to 12m must have a buoyant heaving line at least 15m in length. This is part of the necessary safety gear to assist in the rescue of individuals who may fall overboard or find themselves in distress while in the water. Radar equipment is generally not a requirement for boats of this size unless specified by local maritime laws, and while a sound signaling device is commonly required, it is not the answer in the context of this question.
The provided references discuss various aspects of boats and water safety but do not explicitly mention equipment required for boats of specific lengths. Nonetheless, these concepts are relevant to maritime safety and navigation overall, such as the importance of sonar equipment for navigation and identifying objects underwater, and the potential for aquatic organisms like Zebra Mussel larvae to be transported on boats, which concerns environmental health aspects of boating.