This is a pool torpido! Im sure everyone has played with one before, this works in a similar way accept you can change its density. By adjusting the infill percentage you can make the toy go faster or slower, float or sink. Its recomended to coat this model in either UV resin or a spray selent so water does not seep inside the model and it will last longer but is not required. The density choice is up to your disgression due to a wide range of filament choices but the default for a roll of bambu PLA is 85%.