Final answer:
Navigation equipment such as sonar is required for boats up to 9m and human-powered pleasure craft. Sonar is effective for spotting large underwater objects but has limitations in resolving smaller items or detailed shapes.
Step-by-step explanation:
Boats up to 9m and all human-powered pleasure craft must have certain navigation equipment. While options like compass, radar, and GPS (Global Positioning System) are commonly used in navigation, the subject question seems to focus on sonar equipment.
Sonar, which stands for Sound Navigation And Ranging, is particularly useful for detecting large underwater objects by sending out sound waves that bounce off these objects. The reflected sound waves are then used to calculate the distance to the object. As the information provided indicates, sonar is adept at spotting and locating large structures such as ships or substantial pieces of aircraft wreckage, but it does not resolve smaller objects or discern detailed object shapes effectively. This limitation means that while sonar can be an essential navigation and safety tool for boats, it may not be suitable for finding smaller items.