I am in the process of sanding the bottom down to bare glass. There are several shallow divits where barnacles were and I am going to fair them with awlgrip or something similar. I was thinking of using an epoxy primer unless there is a better way. I am not sure if I need to go all the way to bare glass on one side because it is not pitted at all. There are 3 layers of paint on the bottom: Top coat sands off very easily (a lot of it came off with a pressure washer), the middle coat is the same color (sorta) and a little tougher but not too bad, the base coat is white and hard as heck to sand. Any thoughts, suggestions, or helpful hints?
Umm... you might want to do a bit more research and reading.... AWLGRIP is a topsides/cabintop paint, not a fairing compound.
Fairing anything with a two-part polyurethane paint is a really laborious and expensive process.
What you want to fair with is thickened epoxy, like West Systems Six10 epoxy.
The top coat is probably an ablative paint...and as such would come off very easily. The middle coat may be a hard epoxy paint or more of the ablative. The base coat is probably gelcoat.... might be a barrier coating, but I doubt it.
After fairing the bottom using thickened epoxy, either West Systems Six10 or better yet, epoxy from epoxyproducts.com thickened with colloidial fumed silica, you'll probably want to give the boat a good barrier coating, especially in any places you got down to bare glass, before bottom painting.
For barrier coating, I generally recommend Interprotect 2000E. I wrote a guide to applying it a while back. Get both the grey and white to make your life simpler.
Alternating the colors helps a lot with determining where you've painted, but it is also very useful for helping you coat the areas around the boat stands. For instance:
The first layer is gray, since the gelcoat is white, and you can paint right up to the boat stand pads. Then you paint a layer of white, and leave about a two-inch margin of gray paint around the pads... then paint a layer a gray and leave a four-inch margin around the pads or about two-inches of white and two inches of gray showing...and then finish with a layer of white—with a six-inch margin around the pads—with two inches of gray, two inches of white and two inches of gray.
Then when you move the boat stands, you can fill in the pads and layer the paint accordingly... adding gray to cover the white square left by the pad.. then white to cover the gray square, and so on.
Also, by alternating colors, you can see if someone has sanded through the barrier coat when you're prepping the boat for re-painting. If there's an area that is gray or grayish, they've sanded through at least the outermost layer of barrier coat. If you had all white, you wouldn't be able to tell if they had sanded down through the barrier coat as easily—if you had all gray, you could tell they sanded through the barrier coat...but not if they've sanded into it...
I hope this helps clear things up a bit.
Then bottom paint. Depending on where you keep the boat, how you sail it, and how you'll store it, will have a lot of bearing on what paint to use.