It should take about two liters of varnish to apply four coats to a tandem canoe or a 17' solo kayak; double kayaks and rowing boats will use more, solo canoes will use less.

Coma Berenice CLEAR SPAR Varnish ($29.95/liter) This spar varnish produces an extremely high gloss, applies readily by brushing or spraying, and has high UV inhibitor protection. We have found this varnish to be the easiest to use; it has great flow out characteristics. You actually get more for your money here because the one liter gives you more material than a quart. You should thin this varnish by about 5% with the HMG Thinner listed below when brushing. This will reduce the viscosity so that your brush marks will flow out within 20 minutes or so.