i recall no difficulty painting the outside white with a single quart of brightside polyuerethane.  this would be using a roller and tipping out with a brush.  

according to the brightside description, a quart should be good for three coats over 100 sqaure feet which seems to confirm my recollection.

https://www.clcboats.com/shop/products/new/interlux-brightsides-one-part-polyurethane-marine-paint.html

i estimate the paint surface of a wherry at between 60 and 70 square feet..significantly less than the 100 square foot reference on the brightside specifications....and i am pretty sure i had some paint left over after i was done.

you can double check with CLC...but i am pretty confident 1 quart is all you need.

h

   one last point, on this.  white covers very well....so i only did three coats.  again the specifications make the point about opacity difference with different colors.  they are definitely correct that yellow takes a lot more coats for it to be solid in color.

h

   I used 750ml of each of International Pre-kote and Toplac and 2.5ltr of Compass varnish for the rails and interior of our tandem.

I am painfully aware of how many coats yellow requires.  I painted my boat with yellow polyurethane.  For this boat, I'm planning to use Perfection, because it wears so well.  They list the coverage as 488 sq. ft. for a quart, so it sounds like a quart of Perfection might give me two or three coats.  The color will be a dark blue, rolled on over gray primer.

And two quarts of varnish?  I am planning on a quart of Flagship/high-Build and a quart of Captains varnish.  I'll use up the Flagship, and switch to Captains.  Sound OK  to you guys?

   sounds like a good plan:)