A shop?
Bottom paint has changed a bit - back in the day there was a choice between hard paint, and ablative paint. The primary difference being that the hard paint would go on, and stay on. But if you let it dry out once on, you had to put another coat on top before launching. The ablative paint would wear away as you moved thru water, so didn’t build up as high, and you could pull the boat in and out without having to do much work on the bottom. You can put an ablative over a hard paint, but not the other way.
The new ‘hybrid’ paints are, as you can imagine, a mix between the two - don’t wear away as fast as an ablative, but don’t build up as high as a hard paint. My understanding is that they are much closer to ablatives.
Before hybrids came along, I used to put a coat of hard in one color( blue), and then cover with an ablative in black. That way at the end of the year anywhere I saw blue, I knew that spot needed a touch up. And with multi season ablative, anything that was still black could be left alone.
Many people will advise an epoxy barrier coat over the gel coat, before first coat of paint; theory being it will prevent the hull from absorbing water and blistering. I don’t believe in that, I think if a boat is going to blister it’s due to shoddy fiberglass work or materials, and will blister no matter what you cover it with - and barrier coats are a scam. but I am not a fiberglass expert, so I am probably wrong.
You should have the bottom sanded before you paint. But not all shops do it that way. The benefit of not sanding is that if some day you want to get rid of the bottom paint entirely, if it wasn’t sanded then the paint won’t be adhered nearly as well, and the gel coat will still be in nice shape. Of course the paint won’t be adhered as well, so you will have more touch up work in your future.
