I am a qualified and experienced watchstander at one of the busiest USCG stations on the great lakes. I AM the guy who you are talking to when you are hailing the coast guard within my station's area of response. My experience has been that 90% of boaters have no clue as to how to effectively and efficiently contact us in an emergency.
The following should be the final word on the all the questions brought up in this thread:
1) Don't panic. Try to remain calm.
2) Hail: "U.S COAST GUARD, US COAST GUARD, US COAST GUARD....MAYDAY MAYDAY MAYDAY...". Speaking clearly, with the microphone a few inches from your mouth. Don't speak to fastly. then listen for a response.
3) have a good position ready when calling the coast guard. Your position is THE most important thing for us. GPS coordinates are the best. If no GPS is availible, try to describe any landmarks you may see around you. Frankly, as we see it, you should not be on a boat with no GPS or at least a very, very good understanding of the body of water which you are planning on boating in. Preparation is key.
4) We will want to know of any other forms of communications you may have. Do you also have a cell phone on board? What is your number? How is your battery life? Do you have a good signal?
5) Nature of Distress. Why are you hailing mayday? Be short and to the point. We will automatically deploy to your location for any distress situation.
6) Number of people on board. How many are adults? How many are children?
7) Are there any medical concerns?
8) A GOOD description of your vessel. A "White boat" is not enough info for us to find you if you are currently in a busy part of the lake with a lot of other white boats.
The key is to Prepare before you go. Most people that we deal with have not prepared properly. Bring a GPS, a radio (know how to use it), a cell phone with a good charge, a map, your local uscg phone number, life jackets for everyone. Make sure your boat has an anchor.
And never hail mayday unless you are actually in distress. Always feel free to contact us, but don't use words like "pan pan" or mayday if you are not in distress.
Honestly, my experience has been that most of our radio distress cases have begun with people very causally hailing stuff like, "uh......hello? hello?.....uh....um....any out there?" Our radios pick up every little radio check from lake huron all the way to buffalo new york. SO, when people who are in genuine distress and urgently need help try to hail us by saying things other than mayday, it makes it very difficult for us to distiguish their call for help from the rest of the people on the lack that are just asking for radio checks...
Hope this helps...