How Are Searches Conducted?

There are whole textbooks written on the science of searching for people, many feature lengthy calculations and derivations but it is true that the most commonly used search patterns used at sea are these three:

These three search patterns are extremely effective when carried out by a party such as the coast guard or the navy, in other words people who have training . We get into problems when boats and crews who are inexperienced or out of practice try to search. Inevitably their patterns will start to drift or their track distance is too large and so on. For this reason the coast guard will generally refuse all offers to help with a search until the situation becomes desperate. The lifeline is clearly going to have to cater to both professional searches as well as those conducted by untrained amateurs. The difference between the two has cost lives in the past. 

My next research session is going to have to begin looking into visibility at sea - how far can you see from a boat? What can the human eye discern at distance? But first, I'm going to go do some sketch modelling.