My Southwester Dory is the sapphire blue. Blue covers really well.  You can easily do it with 3 quarts. I’m still working on the inside so can’t tell you about varnish.   

   I just repainted the hull on my NED. Two coats used just under one quart. I also painted two coats of paint over the interior varnish and used about a half quart. I have modified the boat with bow and stern enclosed chambers as well as side thwarts between the second and third frames which are varnished so that would mean more paint but still less than the balance of the quart.