Designed this buoy for RC sailing for instance with the RG65 and Micro Magic class. Designed two parts to avoid the use of a support structure.
The top part must be printed with a fill setting of 3-5% and a wall thickness of around .8mm. This ensures a hollow part. The bottom part can be printed with a fill setting of 40%.
The hole in the bottom parts needs to be filled with led bullets fixed with some wood glue. 15 mins epoxy can be used to glue both parts together.
After gluing use either polyester or spray paint to ensure a a watertight part.