JT,
You think you are confused

try sitting in my chair.
Here is how I start.
I pick an area.
I then concentrate on that area.
I then pass my hand (open) over that area very slowly.
I pay very close attention to what I feel.
By the way I first put a sheet of clear plastic over the map/chart. This is so I can mark it when I feel a spot that is of interest without messing up the map.
I then start my serious dowsing.
As far as Oregon is concerned there was no reason to dowse the area because I had already found gold.
You must remember that when dowsing you are looking for a small area and for a particular item.
No matter how good someone is you must also remember that if you are looking for say "gold" you may also come across every Pawn Shop and Jewelry Store which would take you years to complete and chances are you will never finish the project.
I think this was the reason that I stopped doing this over 30 years ago. It just got to be to much of a strain and don't forget YOU MUST CHECK OUT EVERYTHING and you must do this when things are quite which means that there can be NO disturbance. You must disconnect your phone.
I have 6 grown children and 13 Grandchildren with 2 Grand kids living with me so the only time I can work is after everyone is asleep. I must also add that this is very stressfull and frustrating at times and sometimes very rewarding.
I have never tried to locate a shipwreck anywhere and as far as my Ghost wreck I was given the general location from day one.
Everyone has a GOD GIVEN TALENT it just takes a while to find out what it is.
Hope this explains a few things.
Peg Leg