Mayday ignored?

[LakeSuperior]

Spent one night watch off the SW coast of Portugal, 2011, listening to VHF chatter on 16. I could clearly receive vessels 200+ miles to the north. Could hear a friend about 150 miles north but when we switched to another channel to talk we could not make contact. It seemed like the super-propogation phenomena lasted 3 or 4 hours. It was an interesting watch.