Divide each grapefruit into 8 sections. Gently remove the peels. Keep the fruit flesh for later use. Use a thin blade knife, remove and discard the white membrane, then cut the peels in two. In a large casserole, poach the peels in water for 30 minutes, drain them and put back in the casserole. Add maple syrup and water, and bring to a boil. Reduce heat, and gently simmer, uncovered, for 2 hours, until the peels become translucent. Remove from heat and let cool. Drain the peels in a strainer. Melt chocolate in a double boiler and coat half of the peels in it. Transfer them onto waxed paper and sprinkle with maple sugar.