You are underway at 10 knots. At 1800 you note a radar contact dead ahead at a range of 10 miles. At 1812 the contact is dead ahead at a range of 8 miles. The estimated speed of the contact is __________.

The estimated speed of the contact can be determined by analyzing the change in range of the radar contact over time. When the radar contact is initially noted at a range of 10 miles at 1800 and then again at a range of 8 miles at 1812, a time span of 12 minutes has occurred.

During this time, your vessel is traveling at a speed of 10 knots, which translates to a distance of approximately 2 miles covered in 12 minutes (1/5 of an hour). The radar contact decreased its distance from 10 miles to 8 miles, indicating that it has moved closer by 2 miles within that same time frame.

If the contact had been moving at any speed greater than zero, the distance would not have decreased by exactly the distance your own vessel covered (2 miles). This leads to the conclusion that the contact must be 'dead in the water,' meaning it is stationary and not moving toward or away from your position. Therefore, the estimated speed of the contact is zero knots, supporting the conclusion that it is dead in the water.