I came across a model of a boat, and I tried to add some wind and cloth simulations to the sails and flags. The sails respond to the wind, but the flags do not, they just fall. In both cases I followed the same procedure:
Get a bunch of vertices to act as the "pinning vertex group", reduce the mass to about 0.02, reduce springing to 1, bending to 0.3, and check self-collision.

Initially, I thought that maybe they were too high to interact with the wind, so I put another wind source beside them, and still nothing. Also of note is the flag on top of the 3rd mast. I have no idea what is going on with that, but I have a feeling that it's a result of the mesh trying to fall, but it keeps interacting with itself to create a mess.
My .blend file


The mesh is actually responding to the wind, but it takes a value of 20k force to make it respond as desired. The flag has a much larger distance to be suspended by the force of the wind so it takes a much greater force. The sails are suspended so they respond much more readily.

Try reducing the mass of the flag so that it doesn't take as much force.

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  • $\begingroup$ I've tried playing with wind strength and cloth mass, but no success. If I raised the wind strength to 20k, the first flag responded pretty well, the middle flag started spinning around the mast, and the third flag was still a mess. I've had similar results when I dropped the mass down to 0.005. $\endgroup$ – Pistol Pete Jan 10 '15 at 17:57
  • $\begingroup$ When I tested it, putting the strength at 20k worked for the last two (Or maybe 200k?). The closest one has other issues. $\endgroup$ – VRM Jan 10 '15 at 17:59
  • $\begingroup$ Yeah, I can't figure what's up with that flag. If I take self-collision off, then it isn't scrunching up, but it has some movement that looks discontinuous. $\endgroup$ – Pistol Pete Jan 10 '15 at 18:09
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    $\begingroup$ Try animating them separately on a different layer, it will be easier to make changes. $\endgroup$ – VRM Jan 10 '15 at 18:55
  • $\begingroup$ As in break them from 5 flags (there are 2 that are a little hidden) in one mesh into 5 meshes? I played around with that. It was a little better, but not great. I'm leaning towards blowing them up and just creating my own flags from scratch. $\endgroup$ – Pistol Pete Jan 10 '15 at 19:00

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