Step 1

Put the cubed watermelon in a blender and blend until liquified. Pour the mixture through a very fine-mesh sieve into a large pitcher and discard the solids. Add the orange juice, lime juice, and rum and stir well. Chill until ready to serve.

Step 2

To serve, add the ginger, beer and float orange sliced in the punch. Fill rocks glasses with ice, pour in the punch, and garnish each glass with a watermelon wedge.