A neckline is usually cut lower in the front than in the back.  A boat neck is simply cut straight across, with the shoulders being narrower and the neckline being wider.  I would stil cut the front down a bit more than the back, just because I thin it is irritating to have the fabric hitting to high on the neck.  I would try it on scrap fabric first - you don't need to do the whole garment or even the whole bodice - just make it wide enough to have it hang from the shoulders.  Once you get it the way you want it you can use this as a pattern to cut a facing as well.