Why would you want to attach a fishing line to a float to the surface? Seems like it is better to keep the helicopter at the surface, so just attach this device to the top of your boom and it will float the whole unit. 2.2 pounds of flotation is plenty of flotation to float your average multi rotor with camera. The total weight of your helicopter and camera is not relevant; it is the density of the total unit relative to either salt or freshwater that matters here. A couple pounds of positive flotation will keep a 200 pound human afloat, but it obviously won't float two hundred pounds of lead. Since these units rely on batteries it seems like two may be wise for redundancy.