Regarding the search, what height of wave brings about whitecaps, foam, and heavy spray? What height of wave then brings about the breakers that one sees in the video that was posted from the Telegraph? Does merely a confused sea cause a lot of foam or does there need to be a good blow over the water as well.
What I am trying to understand is how calm the sea and wind needs to be for even decent SAR spotting? I know they deploy in pretty foul weather, but I can imagine that a lot of white on the water makes the challenge a difficult one at best.
Uncle Fred, others have posted the various tables of Beaufort wind scales, sea state, etc. All I can add is an experienced searcher's perspective. Firstly, I think the video posted very recently gives a dramatic example of how difficult any sort of search can be under these conditions. In my opinion, the useful search range from the bridge of that vessel is going to be a couple of hundred yards, MAXIMUM!
Strong winds whip up the sea. Gradually, waves develop. Over a period of time a wind covering hundreds of miles causes the ocean to develop a swell. Wave-like, these swells can have enormous wavelengths and in open oceans 150m to 700m may not be uncommon. Local winds can produce waves on top of an established swell. If the wind is from a different direction to the swell, the surface will be even more disturbed. These local waves, depending on their wavelength compared with the wavelength of the swell they ride upon, may break and produce local white water. Anything that produces waves and/or swell will periodically mask anything afloat. Anything that produces white water will also detract from an observer's ability to see a solid object afloat or riding in neutral buoyancy at some depth under the surface.
Continued strong winds will, at a given rate, "rip" the tops of the waves and blow the spume downwind. In sea state 8 or more, all you can sea are lines of spume set in the direction of the wind. And a very difficult spotting environment this is.
To overcome the masking of something afloat by the presence of the waves and the swell, you need elevation. Too much elevation risks missing anything small!!
To the high swells from the Southern Ocean (lets face it, the area under consideration is on the borderline Indian/Southern Ocean) and the waves from recent strong winds in the search area, you must add the spume and local breakers to the factors that diminish an observer's ability to recognise a person or an object in the water.
A RADAR search of the surface may not be put off by the muddled visual spectrum of white and blue water. But swell and wave height will mask RADAR returns and even return unwanted ones called "clutter". And given that what may or may not be on the surface is almost certainly not going to be generously RADAR-reflective, that's not an enormous help either.
I have only experienced Nimrods as a search platform. At 200 feet, if you mentally extended the 4A tanks forward, you were looking at about 3 nautical miles from the aircraft. A similar exercise with the wingtips or Loral pods, 5nm. Looking for something the size of a person even out to 3nm is not easy, and even if they are wearing a dayglo vest. 5nm? Forget it!
This is an enormously difficult task in an enormously difficult and unfriendly part of the world.