Just to confuse; used to use 2L Optima on my 38' fin keeler (excluding 30cm waterline strip that I did in trilux ; 1 small tin per season). That gave 2 (thin) coats and another on the rudder, leading edges, P-bracket, etc. Worked well.
5 litres for Westerly Centaur, bilge keels, 2 coats plus 3rd coat on rudder, waterline and leading edges. Roller application. Boat lifted every three years.