Search Patterns for Sailors
Its late at night and youre sailing downwind in a moderate breeze. You hear a faint scream, quickly go up top to investigate and discover, to your horror, that no one is on deck. Apparently, your shipmate has fallen overboard. You hit the MOB function on the GPS, get the boat turned upwind and proceed to the approximate spot where your companion fell overboard. He is nowhere to be seen.
The water temperature is only 55 degrees; it is critical that you find your shipmate as soon as possible. You call the Coast Guard for assistance, but you are 30 miles offshore, and it will be quite a while before help arrives. By then hypothermia will have set inor worse. Your sailing companions best hope is for you to find him or her yourself. But which way should you steer? How far should you go? When should you change course? To answer these questions you need to know how to execute a simple search pattern.
Search patterns are useful in other situations as wellfor example, if a piece of valuable (and buoyant) equipment falls off the boat, or your dinghy gets loose. Although MOB emergencies and these other sorts of events tend to be rare occurrences, they are not out of the question. One day your ability to conduct an effective search could be a true lifesaver. Sophisticated search and rescue (SAR) operations are best left to the Coast Guard and other professional agencies, as it takes extensive training and practice to become proficient at these. However, there are some basic techniques that you can apply in an emergency. Lets start with three key concepts: datum, search pattern and track spacing.
Datum: This is the most probable location of an object in the water, after correcting for such offsetting factors as current and wind.
Search Pattern: This is a predefined pattern, a set series of courses and distances that rescuers will follow while searching for an object in the water. There are six common search patterns and numerous variations.
Track Spacing: Track spacing is the separation distance between the various legs of a search pattern: the tighter the track spacing, the higher the likelihood of locating an object in a particular area. However, tighter track spacing also decreases the size of the area being searched and/or increases the time required to conduct a search over a particular area.
The Coast Guard uses sophisticated computer modeling to determine datum and construct an optimal search pattern and track spacing. Since you almost certainly wont have access to such resources, lets look at two scenarios that should cover a variety of situations. The search patterns described below are adapted from professional techniques, but I have simplified them to make them practical for the average recreational sailor.