In a large serving pitcher, combine silver rum, spiced rum, orange juice, grapefruit juice, lemonade, limeade, fresh lime juice, and ginger simple syrup. Keep chilled in the fridge until ready to serve.
Serve rum punch over ice. Garnish with sliced lime, fresh mint, and maraschino cherries. If desired, splash chilled sparkling water or club soda to reduce potency of cocktail.
Notes
To make ginger simple syrup: bring to a boil 1 cup water, 1 cup granulated sugar, 3-inch fresh ginger (skin peeled, ginger sliced into thin disks). Remove from heat and allow sliced ginger to steep for 30 minutes. Strain out ginger and let simple syrup cool to room temperature. Transfer to container and store in the fridge for up to one month.
If desired, splash chilled sparkling water or club soda to reduce potency of cocktail