Scotius, what level of force do you think the harpoon will be exerting. Also, ballast is a key component to airships and modulating the lift that the lifting bags exert. The craft uses fuel and a neutral or slightly negative buoyancy is what one wants close to the ground. Too much lift and you risk going out of control, exceeding pressure height and venting your lifting gas. Then when you come back down you'll be over weight. Look at the details on the US Navy's Airships. They went to great lengths to setup a ballast release system as well as condensers to retain some of the water from engine exhaust and to use that as ballast. This reduced the amount of lift gas venting necessary to maintain boyancy in a controllable range. As to anchors, correctly speaking, you need a weight of earth or material upon that anchor to act as enough ballast for such an object. A few inches of harpoon barb would be poor at best and would rip out. NAS Lakehurst has multiple tie down points of steel eye hooks embedded in concrete cast into the ground. There were also very substantial anchor points for the high-mast plus other equipment. Naval Anchors work as I said laterally. They can act due to weight, but the forces on the ship are laterally and not as much vertically. If a ship is anchored and very close it it's anchor it will pull it's anchor up and drag under the force of currents. Anchors work basically like a plow and dig in that way. There are differences in types for types of sea bottom and amounts of weight vs shape for various levels of function. http://www.christinedemerchant.com/anchor_styles.html