When should you reduce your speed so that you can stop your vessel if necessary?

You should reduce your speed when navigating in areas with limited visibility, such as fog or heavy rain, to ensure you have enough time to react to obstacles or hazards. Additionally, slowing down is important in crowded waters or when approaching navigation markers, docks, or shallow areas. It's also prudent to reduce speed when the weather conditions are poor or when you notice other vessels behaving unpredictably. Always be prepared to stop quickly if the situation demands it.