Final answer:
A navigator can keep a ship in safe waters by maintaining a course where the two lighthouses at points A and B remain aligned outside of the dangerous 300-degree arc. The alignment acts as a guide to stay clear of the rocks between the lighthouses.
Step-by-step explanation:
To keep the ship in safe waters while navigating between two lighthouses at points A and B, a navigator should maintain a course that keeps the lights from A and B aligned in a manner that the ship does not cross the unsafe 300-degree arc AXB. If the lights of A and B are in line with each other when viewed from the ship, the navigator is directly on the line connecting A and B. The navigator should keep this alignment to a bearing which ensures that the ship stays outside of the dangerous arc.
By continuously adjusting the ship's bearing to keep the lighthouses aligned and out of the 300-degree dangerous arc, the navigator will ensure the ship remains in safe waters. It's important to note that this method relies on having a clear view of both lighthouses and good visibility conditions.